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Tracking Fluid Movement During Cyclic Steam Stimulation of Clearwater Formation Oil Sands Using Stable Isotope Variations of Clay Minerals
Abstract
In situ thermal recovery methods such as cyclic steam stimulation (CSS) are required to extract highly viscous bitumen from the Clearwater Formation oil sands of Alberta, Canada. The injection of hot fluids during CSS has altered the mineralogy of the sands, resulting in the loss of some minerals (e.g. disseminated siderite, volcanic glass) and precipitation of others (e.g. zeolites and abundant hydroxy-interlayered smectite). The high temperatures and high water – rock ratios associated with CSS might also alter the oxygen and hydrogen isotopic compositions of pre-existing clay minerals even in the absence of mineralogical changes. The present study exploits this fact to track the movement of injected hot fluids during CSS. Berthierine, a common diagenetic clay mineral in the Clearwater sands, survived CSS but acquired substantially lower δ18O and δ2H values in cores located 4 10 m from the injection well. In contrast, the oxygen and hydrogen isotopic compositions of berthierine in cores located further from the injection well were generally unaffected, except at the depth of steam injection where horizontal fractures facilitate greater lateral penetration of hot fluids. Smectitic clays in near-injector cores also acquired lower δ18O values during CSS, but a systematic shift in δ2H values was not observed. While hydrogen-isotope exchange undoubtedly occurred, the particular combination of temperature and H isotopic composition of the injected fluid used during CSS appears to have yielded post-steam δ2H values that are indistinguishable from pre-steam values. Only samples from near-injector core G-OB3 that contain hydroxy-interlayered smectite have lower δ2H values as a result of CSS.
... High temperatures during CSS initiate chemical reactions between injected steam, formation fluids, and minerals and rock fragments in oilsands. These reactions can reduce permeability and hence hydrocarbon recovery through formation of clay minerals, physical migration of claysize particles, and precipitation of carbonate in reservoir pore spaces (Hutcheon, 1984;Hebner et al., 1986;Kirk et al., 1987;Fialka et al., 1993;Zhou et al., 1993Zhou et al., , 1994Zhou et al., 1995;McKay and Longstaffe, 2013). Insitu hydrocarbon recovery from oil-sands requires a full understanding of these processes. ...
... Among the three major oil-sands deposits in Alberta (Fig. 1), those at Cold Lake are the second largest with the Clearwater Formation being the most prolific bitumen reservoir, with reserves estimated at about 11 × 109 m 3 of heavy crude bitumen (Alberta Energy and Utilities Board, 1996). Much of the Clearwater Formation comprises shaley, clast-rich sands containing abundant clay minerals (Hutcheon et al., 1989;McKay and Longstaffe, 1997;Zhou et al., 1994;McKay and Longstaffe, 2013). Berthierine is commonly most abundant; in some sections of the Clearwater Formation, it can comprise up to 80-90% of the clay mineral sizefraction. ...
... The oxygen and hydrogen isotope compositions of clay minerals were analyzed at LSIS, the University of Western Ontario. Prior to isotopic analysis, the clay minerals were heated under active vacuum at 150 • C for a minimum of 12 h to remove interlayer water and water adsorbed on the the surfaces (McKay and Longstaffe, 2013). Isotopic analysis then proceeded without any further exposure of the samples to the atmosphere. ...
Chemical reactions between oil-sands and injected steam or steam condensate during cyclic steam stimulation (CSS), commonly used to mobilize heavy oil and bitumen, result in decomposition of pre-existing minerals and formation of new phases including clay minerals. These changes can reduce reservoir permeability and limit hydrocarbon recovery. In this study, the chemical and stable isotope compositions of berthierine and smectitic clay minerals contained in pre- and post-steam Clearwater Formation oil-sands from Cold Lake, Alberta were analyzed to investigate how these phases were affected by CSS. Berthierine abundance in the injection-zone decreased after steaming whereas the abundance of smectitic clay minerals increased. Pre- and post-steam berthierine exhibited the same range of chemical compositions, while those of pre- and post-steam smectitic clay minerals commonly differed. Some post-steam smectitic clay minerals from the steam injection-zone, in particular, contain significantly more Fe and Si but less Al than pre-steam samples. It is proposed that that berthierine contributed to the formation of new smectitic clay minerals during CCS through partial inheritance of the berthierine 1:1 structure. This inheritance model approximates the unique chemical compositions of the post-steam smectitic clay minerals. The model also helps to explain the incomplete oxygen and hydrogen isotope exchange between injection fluids and smectitic clay minerals formed during CSS.
... High temperatures during CSS initiate chemical reactions between injected steam, formation fluids, and minerals and rock fragments in oilsands. These reactions can reduce permeability and hence hydrocarbon recovery through formation of clay minerals, physical migration of claysize particles, and precipitation of carbonate in reservoir pore spaces (Hutcheon, 1984;Hebner et al., 1986;Kirk et al., 1987;Fialka et al., 1993;Zhou et al., 1993Zhou et al., , 1994Zhou et al., 1995;McKay and Longstaffe, 2013). Insitu hydrocarbon recovery from oil-sands requires a full understanding of these processes. ...
... Among the three major oil-sands deposits in Alberta (Fig. 1), those at Cold Lake are the second largest with the Clearwater Formation being the most prolific bitumen reservoir, with reserves estimated at about 11 × 109 m 3 of heavy crude bitumen (Alberta Energy and Utilities Board, 1996). Much of the Clearwater Formation comprises shaley, clast-rich sands containing abundant clay minerals (Hutcheon et al., 1989;McKay and Longstaffe, 1997;Zhou et al., 1994;McKay and Longstaffe, 2013). Berthierine is commonly most abundant; in some sections of the Clearwater Formation, it can comprise up to 80-90% of the clay mineral sizefraction. ...
... The oxygen and hydrogen isotope compositions of clay minerals were analyzed at LSIS, the University of Western Ontario. Prior to isotopic analysis, the clay minerals were heated under active vacuum at 150 • C for a minimum of 12 h to remove interlayer water and water adsorbed on the the surfaces (McKay and Longstaffe, 2013). Isotopic analysis then proceeded without any further exposure of the samples to the atmosphere. ...
Chemical reactions between oil-sands and injected steam or steam condensate during cyclic steam stimulation (CSS), commonly used to mobilize heavy oil and bitumen, result in decomposition of pre-existing minerals and formation of new phases including clay minerals. These changes can reduce reservoir permeability and limit hydrocarbon recovery. In this study, the chemical and stable isotope compositions of berthierine and smectitic clay minerals contained in pre-and post-steam Clearwater Formation oil-sands from Cold Lake, Alberta were analyzed to investigate how these phases were affected by CSS. Berthierine abundance in the injection-zone decreased after steaming whereas the abundance of smectitic clay minerals increased. Pre-and post-steam berthierine exhibited the same range of chemical compositions, while those of pre-and post-steam smectitic clay minerals commonly differed. Some post-steam smectitic clay minerals from the steam injection-zone, in particular, contain significantly more Fe and Si but less Al than pre-steam samples. It is proposed that that berthierine contributed to the formation of new smectitic clay minerals during CCS through partial inheritance of the berthierine 1:1 structure. This inheritance model approximates the unique chemical compositions of the post-steam smectitic clay minerals. The model also helps to explain the incomplete oxygen and hydrogen isotope exchange between injection fluids and smectitic clay minerals formed during CSS.
... In field tests, Longstaffe (1994) and McKay and Longstaffe (2013) demonstrated the occurrence of oxygen-and hydrogen-isotope exchange between the injection fluids and clay minerals during CSS of Clearwater Formation reservoirs. The change in oxygen-and hydrogenisotope compositions between pre-and post-steam clay minerals provides insight into the extent of interaction between clay minerals and steam/steam condensate. ...
... During CSS, the water/mineral ratio for both oxygen and hydrogen may not be as high as that in the autoclave experiments, and the factors affecting the resulting isotope compositions of injected water are much more complex (McKay and Longstaffe, 2013). In addition to water-rock interaction, interaction between steam and hydrocarbons can cause changes in the stable isotope compositions of the production waters, especially for hydrogen (McKay and Longstaffe, 2013). ...
... During CSS, the water/mineral ratio for both oxygen and hydrogen may not be as high as that in the autoclave experiments, and the factors affecting the resulting isotope compositions of injected water are much more complex (McKay and Longstaffe, 2013). In addition to water-rock interaction, interaction between steam and hydrocarbons can cause changes in the stable isotope compositions of the production waters, especially for hydrogen (McKay and Longstaffe, 2013). Such interaction could lead to lower than expected δ 2 H for the co-existing clay minerals (Sheppard, 1986;Fallick, 1993;McKay and Longstaffe, 2013). ...
In an effort to evaluate mineral-water isotopic exchange during cyclic steam stimulation (CSS), solutions and <2 μm berthierine-dominated solids from the Clearwater Formation oil sands of Alberta, Canada were analyzed for stable isotope compositions before and after reaction in autoclaves for 1008 h at 250 °C. There was no significant change in solution δ ¹⁸ O and δ ² H, which is consistent with the high water/mineral ratio used in the experiments. The solids showed a marked decrease in both δ ¹⁸ O and δ ² H following the experiments. Pre-run solids have δ ¹⁸ O of +9.5 to +12.9‰ and δ ² H of −114 to −113‰, whereas post-run solids have δ ¹⁸ O of −4.7 to +2.1‰ and δ ² H of −147 to −128‰. Neither oxygen- nor hydrogen-isotope equilibrium was established between the solids and the solutions. Calculation suggests that oxygen-isotope exchange (44–58%) was greater between the solids and the solutions than was the case for hydrogen isotopes (23–50%). We propose that this behaviour resulted from partial inheritance of the pre-run berthierine structure during formation of the post-run smectite, chlorite-smectite and chlorite. This process confounds the use of clay mineral stable isotope compositions as a temperature indicator of in situ steam/steam condensate interaction with oil-sands reservoirs. The results also suggest an additional mechanism by which new clay minerals can be formed during CSS-related, artificial diagenesis.
... 14 These reactions could reduce reservoir permeability because of the formation of clay minerals, migration of clay particles, and precipitation of carbonates. 15 Additionally, the frequently occurring gas channeling phenomenon could sharply reduce steam sweep efficiency. 16 Therefore, it is necessary to improve the technology for producing heavy oil. ...
... The plot of low δ 18 O and δD values of smectite samples between the smectite line at 60 • C and meteoric water line environment at temperatures above 80 • C suggests the mixing of high-temperature steam with low δ 18 O value meteoric water (McKay and Longstaffe, 2013;He and Longstaffe, 2022). The narrow δD values suggest the more effect of meteoric water in the occurrence of smectite (Simpson et al., 2022). ...
Mineralogy, geochemistry, and genesis of lithium-bearing argillaceous
sediments associated with the borate deposit.
... The plot of low δ 18 O and δD values of smectite samples between the smectite line at 60 • C and meteoric water line environment at temperatures above 80 • C suggests the mixing of high-temperature steam with low δ 18 O value meteoric water (McKay and Longstaffe, 2013;He and Longstaffe, 2022). The narrow δD values suggest the more effect of meteoric water in the occurrence of smectite (Simpson et al., 2022). ...
Lithium distribution in Bigadiç Borate Deposit and lithium-borate relations
... where R is the ratio of the heavy isotope ( 2 H) to the light isotope ( 1 H) of the sample material relative to the isotope ratio of an international measurement standard, "std", such as, Vienna Standard Mean Ocean Water (VSMOW). The measured δ 2 H, however, may not be representative of expandable clay minerals such as smectite if strongly bound water (SBW) is not fully removed prior to isotopic analysis (e.g., Marumo et al., 1995;McKay and Longstaffe, 2013). Previous studies have described a range of heating (degassing) temperatures and times for complete removal of adsorbed water from clay mineral surfaces, especially smectites (Bérend et al., 1995;Van-DeVelde and Bowen, 2013;Bauer and Vennemann, 2014;Kuligiewicz and Derkowski, 2017). ...
Atmospheric water adsorbed onto clay mineral surfaces, of smectite group minerals in particular, can contaminate hydrogen released from structural hydroxyl groups during hydrogen-isotope analysis. Interlayer cation composition and cation hydration enthalpy, in particular, can affect the magnitude of this excess hydrogen yield and hence the hydrogen isotope composition (δ²H) of smectites. To evaluate this problem, δ²H of different cation-saturated (Ca²⁺, Na⁺, K⁺), dried forms of six smectite standards from the Clay Minerals Society Source Clays were measured using a modified sample drying and on-line High-Temperature-Conversion-Elemental-Analysis (TCEA) Continuous-Flow-Isotope-Ratio-Mass-Spectrometry (CF-IRMS) protocol. More negative interlayer cation hydration enthalpies (Ca²⁺ > Na⁺ > K⁺) led to higher residual adsorbed water contents, which produced poorer δ²H reproducibility for the determination of smectite hydroxyl hydrogen. The lowest adsorbed water contribution and the most reproducible and possibly accurate δ²H for smectite hydroxyl hydrogen was obtained for K-saturated smectites dried for both 4 and 24 h at 220 °C prior to isotopic analysis and transferred to a “Zero-Blank” autosampler in ≤2.5 min. This approach provided the lowest measurement error for hydroxyl δ²H and facilitated much greater sample throughput than classical methods for smectitic clays. This study proposes a protocol for hydroxyl δ²H determination in smectitic clay minerals, and reveals the effect of H-isotope fractionation of adsorbed water during sample preparation.
... Powder X-ray diffraction (pXRD) patterns were obtained for each Simpson et al. Chemical Geology 588 (2022) 120639 subsample in order to identify clay minerals using the following protocol adapted from Ignasiak et al. (1983) and McKay and Longstaffe (2013). ...
The peak-ring of the 66 Ma, ~180 km Chicxulub impact structure in the northern Yucatán peninsula and southern Gulf of Mexico was sampled during the International Ocean Discovery Program and International Continental Scientific Drilling Program (IODP–ICDP) Expedition 364 at Site M0077 (21.45° N, 89.95° W). Secondary clay minerals are pervasive throughout the upper peak-ring lithologies as a product of ubiquitous altered glass present throughout the impact melt and melt-bearing breccia sequence. Here we present the first detailed study of the clay mineralogy (microprobe, pXRD, spectral reflectance from 350 to 2500 nm) and isotope geochemistry (δ²H and δ¹⁸O) of the <0.2 μm size-fraction from upper peak-ring lithologies. The clay mineralogy is dominated by smectitic clay minerals, whose composition varies with stratigraphic position. Trioctahedral MgFe smectite (var. saponite) is most common in Units or Subunits 2A, 2C, 3 and 4, while a section of Subunit 2B contains a more dioctahedral, Al-rich smectite. Higher porosity regions of the lower to mid, dioctahedral smectite-dominated intervals have higher δ¹⁸O (+14.2 to +18.6‰) whereas intervals dominated by trioctahedral smectite have lower δ¹⁸O (+10.4 to +14.1‰). The range of smectite δ²H (−105 to −87‰), in comparison to that of oxygen isotopes, is proportionally much less variable and unrelated to smectite mineralogy. When combined, the oxygen and hydrogen isotope compositions of the smectitic clay minerals suggest low temperature (~20 to 50 °C) formation from meteoric water-dominated fluids. The lower end of this temperature range is below current ambient conditions, which conceivably could suggest smectite formation before much of the overlying sedimentary rocks were deposited (~56 Ma?). Calculated temperatures are generally lower than those associated with impact-generated hydrothermal alteration.
Calculated δ¹⁸O and δ²H of meteoric water-dominated fluids associated with low-temperature formation of these clay minerals are lower than known for modern meteoric water in the Yucatán region. The simplest explanation for the source of these ancient fluids is meteoric water-dominated Gulf Coast brines. A more remote possibility is orogenically-driven, long-distance transport of groundwater from highlands to the east via an artesian aquifer formed in part by fractured Mesozoic rocks extending laterally beneath the impact structure.
The ~180-km-diameter Chicxulub peak-ring crater and ~240-km multiring basin, produced by the impact that terminated the Cretaceous, is the largest remaining intact impact basin on Earth. International Ocean Discovery Program (IODP) and International Continental Scientific Drilling Program (ICDP) Expedition 364 drilled to a depth of 1335 m below the sea floor into the peak ring, providing a unique opportunity to study the thermal and chemical modification of Earth's crust caused by the impact. The recovered core shows the crater hosted a spatially extensive hydrothermal system that chemically and mineralogically modified ~1.4 × 10 5 km 3 of Earth's crust, a volume more than nine times that of the Yellowstone Caldera system. Initially, high temperatures of 300° to 400°C and an independent geomagnetic polarity clock indicate the hydrothermal system was long lived, in excess of 10 6 years.
The equilibrium H- and O-isotope fractionations can be approximated by the following equations which are based on experimental, empirical and/or theoretical data:
Hydrogen: 1000 ln α kaolinite-water = −2.2 × 10 ⁶ × T ⁻² − 7.7
Oxygen: 1000 ln α kaolinite-water = 2.76 × 10 ⁶ × T ⁻² − 6.75
1000 ln α smectite-water = 2.55 × 10 ⁶ × T ⁻² − 4.05
1000 ln α illite-water = 2.39 × 10 ⁶ × T ⁻² − 3.76
The equilibrium H-isotope fractionation factors vs . 10 ⁶ × T ⁻² for kaolinite and probably smectite and illite are monotonic curves between 350-0°C. More complex curves, with a minimum fractionation near 200°C, are probably influenced by surface effects and/or disequilibrium fractionations among the different hydrogen sites. The H-isotope fractionations between smectite-water increase by ~70‰ from Fe-poor montmorillonite to nontronite at low temperatures. The pore-interlayer water in smectite H-isotope fractionation at low temperatures is ~20±10‰. The presence of organic matter can modify both the δD value of the clay analysis and its ‘water’ content. Clays — kaolinite, illite, smectite and probably halloysite — tend to retain their D/H and ¹⁸ O/ ¹⁶ O ratios unless subjected to more extreme diagenetic or metamorphic conditions or special local processes. Kinetic information is still only qualitative: for comparable grain sizes, hydrogen exchanges more rapidly than oxygen in the absence of recrystallization. Low-temperature diffusion coefficients cannot be calculated with sufficient precision from the higher temperature exchange data. The H- and O-isotope studies of clays can provide useful information about their conditions of formation.
Berthierine occurs as pore-linings of well crystallized laths of variable thickness in oil-sands of the Clearwater Formation, Alberta, Canada. Berthierine crystallized early in diagenesis within portions of a deltaic/estuarine complex dominated by brackish to fresh water.
Separates prepared using high gradient magnetic separation contain approximately equal amounts of monoclinic and orthohexagonal berthierine. Minor, but variable, quantities of inseparable, iron-rich impurities mainly consist of chamosite Ib and IIb, and Fe-rich smectitic clays.
Clearwater Formation berthierine has a range of chemical compositions that differ from those reported for most other berthierines. The SiO 2 (27-35 wt%), Fe 2 O 3 (5-8 wt%) and Al 2 O 3 (16-18 wt%) contents for Clearwater Formation berthierine fall between values normally reported for berthierine and odinite. The average structural formula of five samples studied in detail is (Fe ²⁺ 1.01 Al 0.82 Mg 0.46 Fe ³⁺ 0.28 Mn <0.01 □ 0.43 )(Si 1.74 Al 0.26 )O 5 (OH) 4 , where □ represents vacancies in the octahedral sheet. The large number of vacancies in the octahedral sheet implies a di-trioctahedral character for this clay. Our results also suggest that a series of compositions can occur between ideal berthierine and odinite end-members.
Berthierine has been preserved within the Clearwater Formation because temperatures during diagenesis did not exceed 70°C, and perhaps also because hydrocarbon emplacement limited subsequent transformation of berthierine to other phases, such as chamosite. Intense, early diagenetic, microbial activity and/ or the strongly reducing environment created by later emplacement of hydrocarbons may be responsible for the Fe ²⁺ /Fe ³⁺ ratio of the berthierine. Because of these conditions, this ratio may have changed since initial clay crystallization. The Clearwater Formation occurrence of grain-coating Fe-rich clays provides valuable insights into possible relationships between the Fe-serpentine minerals, odinite and berthierine, and supports an important role for these phases as precursors to the grain-coating and pore-lining Fe-chlorite (chamosite) that is so common in ancient sandstones, including many hydrocarbon reservoirs.
A technique has been developed in which bromine pentafluoride is used as a reagent for quantitative liberation of oxygen from oxides and silicates. For all of the rocks and minerals analysed, the oxygen yields are 100 ± 2 per cent of the theoretical amount. The advantage over techniques involving reduction with carbon lies in the consistently better oxygen yields, with consequent decrease in systematic errors in isotopic composition. Bromine pentafluoride has advantages over fluorine in being easier and safer to handle in the laboratory, in being readily purified, and in reacting with some minerals which do not react completely with fluorine. The results of isotopic analyses are compared with measurements made in other laboratories by other procedures.
Ferromagnesian minerals (biotite, amphibole, pyroxene) are common within some oil-saturated sandstones. Orthoclase and plagioclase (An4-An60) occur; accessories include clinoptilolite.-P.B.
A laboratory study was completed to determine the interaction between the condensate and Cold Lake oil sand during steam stimulation. Results indicate that steam condensate flooding affects the sand by reducing permeability, increasing the amount of material in the less than 38 mu m size fraction, decreasing dolomite content, decreasing kaolinite content in the finer fractions, producing CO//2, precipitating smectite rims on framework grains, and precipitating calcite in pore spaces. Smectite growth is the main cause of permeability reduction because it increases the amount of material in the pore spaces and it creates a microporosity network that restricts flow.
Meteoric water was present during early diagenesis of some sandstones simply because they were deposited in fluvial environments. In other cases, deposition in transitional fresh-water to marine settings resulted in a variable but nevertheless significant meteoric contribution to early pore waters. Diagenesis of the Lower Cretaceous Clearwater Formation oil sands, for example, has been substantially influenced by the prevalence of meteoric water early in their history. The influx of low-18O water dominated late diagenesis of most sandstones, resulting in formation waters largely controlled by mixing between the post-Laramide, meteoric flux and earlier, more evolved pore waters. -from Author
The oxygen and hydrogen isotope compositions of diagenetic minerals can be used to provide constraints on the origin and evolution of porewaters during the life cycle of a sedimentary basin. In the first part of this chapter, general controls on the oxygen and hydrogen isotope fractionations in diagenetic systems are discussed. In the second part, stable isotope results for diagenetic minerals from sandstones and conglomerates of the western Canada sedimentary basin are reviewed as an example of this approach. This review illustrates the importance of meteoric water throughout the diagenetic evolution of these rocks. For many units, the isotopic data show that meteoric water was abundant during early diagenesis, either because of depositional environment or because of early, post-depositional processes related to sea-level fluctuation. During burial, the oxygen isotope values of porewaters increased not only because of rock-water interaction, but also because of mixing with brines derived from underlying Paleozoic carbonates. The oxygen isotopic compositions of late diagenetic minerals indicate crystallization during regional, gravity-driven flow of meteoric water that was initiated in response to uplift of the western Canada sedimentary basin in early Eocene time.
The literature pertinent to the fluid-rock interactions that may occur during in situ recovery of bitumen by wet thermal methods and to the consequent deterioration of reservoir properties is briefly reviewed. Dissolution and precipitation of SiO//2 are discussed in terms of its movement and deposition during in situ processes and an analytical expression for quartz dissolution rate is presented. The results of this study show that it is very likely that montmorillonite will form during in situ recovery of bitumen from the Athabasca oil sands by steam injection and that other mineral reactions are also possible.
One method of in situ extraction currently being considered for use in the Alberta Oil Sands is Wet Forward Combustion, a process which generates both hydrothermal and high-temperature conditions in the formation. Some of the mineral transformations that may occur under these conditions have been studied in the laboratory with the use of bomb-type autoclaves and a firetube. Montmorillonite was found to form rapidly under hydrothermal conditions from mixtures of kaolinite, quartz and dolomite - minerals that are frequently present in the Alberta deposits.
A portion of the Countess B petroleum reservoir in the Lower Cretaceous Glauconitic Sandstone located near Brooks, Alberta, which had initially been waterflooded, was converted to wet in situ combustion. A mineralogial examination of a post-combustion core from this pilot was used to determine the water-rock reactions that occurred in the reservoir during combustion.-from Authors
There are abundant clay occurrences in the oil sand reservoirs in the Clearwater Formation at Cold Lake. It has been suggested that hydrothermal reactions of the clay minerals may cause permeability damage during thermal recovery. To quantify such damage, two corefloods (BCF1 and BCF2) were conducted at 250 ° C. During the corefloods, three periods of permeability damage were recognized. The first period of permeability damage occurred during and shortly after the core was heated to 250 ° C. Experimental evidence suggests that thermally activated grain crushing and subsequent fines migration were responsible for this initial permeability decrease. The second period of permeability damage was a gradual process but resulted in 65% (for BCFl) to 78% (for BCF2) permeability loss. Hydrothermal reactions (berthierine to Fe-saponite) are considered to be responsible for this significant permeability damage. The third period of permeability damage took place when fresh water was injected into the core. Osmotic swelling of the Fe-saponite (the hydrothermal clay formed during the coreflood) was considered responsible for this damage.
A recent study by McKay and Longstaffe (1994) indicated that berthierine was still present in a post-steam core 20 m away from a injection well in Cold Lake area. The inconsistency between laboratory experiments and field observation may be due to the kinetics of the reactions. The rate of silicate/aqueous solution reaction at 150 ° C is 20 times slower than that at 250 ° C. The lack of field evidence for the berthierine reactions may be due to the reaction being localized near the well bore. There is some field evidence for the disruption of berthierine grain coats and permeability damage due to subsequent fines migration. Regardless of the mechanism by which berthierine impacts permeability, field and experimental results suggest that completion intervals should avoid berthierine-rich horizons.
Introduction
It has been widely recognized that the clay minerals can cause formation damage to hydrocarbon reservoirs. Berthierine is among the most abundant diagenetic clay minerals in the Clearwater Formation at Cold Lake (Abercrombie, 1988; Longstaffe, 1990; Hornibrook and Longstaffe, 1996). Petrographically, the berthierine in the Clearwater Formation is present as coatings on the sand grains. Due to its surface coating nature and Fe-rich composition, the Cold Lake berthierine may react with injection fluids and thus affect reservoir quality (Zhou et al., 1995).
To demonstrate the effect of hydrothermal reactions on reservoir permeability, two hydrothermal corefloods were performed. This paper describes methods and results of the corefloods, and discusses their implications. Field evidence was gathered to compare with the experimental observations. The cause for the discrepancy between the laboratory and field observations is discussed.
Coreflood Experiments
Sample Preparation
The oil sand sample used in this study was from Imperial Oil's Cold Lake lease (434–442m, 6-21-65-4W4). The oil sands in this sample represent a relatively poor portion of the Cold Lake reservoir in that it is semi-consolidated due to abundant berthierine cement. Abundant berthierine cement can cause the initial bitumen content to be less than a third of that in a good oil sands.
The 18O/16O and D/H ratios of the structural oxygen and hydrogen of naturally occurring clay minerals carry information about the conditions under which the minerals formed. Clays generally form in isotopic equilibrium with the environment, and hence have isotopic compositions that reflect the temperature of formation and the 18O/16O and D/H ratios of water in the micro-environment. The isotopic signature of water in the weathering environment is a reflection of the climate. Once formed, clays are resistant to isotopic alteration under surface and near-surface conditions, except when they undergo subsequent mineralogical alteration. In some instances, this alteration may be subtle, as in the case of conversion of kaolinite with a high degree of crystalline order (as measured by the Hinckley index) to kaolinite of low crystalline order in a pedogenic profile. Isotopic studies of pedogenic clays may be expected to yield more information about pedogenesis and paleoclimate when both 18O/16O and D/H ratios of the clays are measured. However, few studies have incorporated the use of the two isotope ratios.
Recovery of highly viscous oil from some of the deeper oil sand deposits of northern Alberta, Canada, is made possible through injection of heat by steam or hot water flooding of the reservoirs. The rise in temperature lowers the viscosity of the bitumen allowing it to be produced. The increase in temperature accelerates the reactions between the matrix and pore minerals of the formation and can produce reaction products which can significantly alter the permeability of the reservoir. If carbonate minerals are present in the reservoir, inorganic CO2 may also be a reaction product.
CO2 is commonly produced during steamflooding. In higher-temperature steamfloods the amount of CO2 produced is such that the only viable source is carbonate minerals. We show by reference to CO2 concentrations in natural geothermal systems that in most common rocks and sediments, CO2 is generated naturally under hydrothermal (~572°F) conditions by the dissolution of carbonate minerals. CO2 solubility is a strong positive function of temperature and, at 572°F, is more than sufficient to account for high CO2 concentrations like those encountered at Chevron's Buena Vista (BV) Hills steamflood pilot test. A linear kinetic model is developed to describe chemical equilibration and CO2 generation in the hot parts of the reservoir. The model also describes CO2 removal through carbonate precipitation in the cooler parts of the rock formation where the fluid moves ahead of the thermal front. Changes in carbon isotope concentration are included in the model. The small difference between the 13C in the produced gas and the source carbonates at BV Hills suggests that little CO2 is precipitated as carbonate within that reservoir, a prediction that can be tested by poststeamflood coring.
Imperial Oil Resources Limited began pilot experimentation with Cyclic Steam Stimulation (CSS) at Cold Lake in 1964 and followed this with commercial application in 1985. Since that time an extensive amount of experimental data and operating experience has been acquired which has resulted in the continual evolution of steaming and operating strategies for CSS.
Optimization of the many process variables involved in CSS is complex due to their interdependency. The optimization of steaming and operating strategies has advanced significantly with commercial development and continues to evolve as the CSS process matures and the reservoir reaches more advanced stages of depletion. This evolution has focussed on steam strategies to manage interwell communication and increase areal conformance, and operating strategies to maximize the efficiency of producing mobilized bitumen which lies at ever increasing distances from the wellbore. The continued success of CSS in Cold Lake is dependent on the continued improvement of these steaming and operating strategies.
Steam stimulation of the Cold Lake bitumen reservoir causes fracturing of the formation. Steam enters via convection along the fracture plane, and heat propagates perpendicular to this plane by conduction, which in some cases may be enhanced by convection. Temperature profiles from observation wells located around stimulated wells directly give the energy distribution at those locations. The analysis can be extended beyond energy distribution by distinguishing regions of convective and conductive heat transfer in the temperature profiles. Simple analytical models can then yield important insights into the cyclic steam stimulation process, such as fracture geometry and fluid flow velocity. Eight field cases are discussed representing profiles from the injection, shut-in, and production phases of the process.
The extent of hydrogen and oxygen isotope exchange between clay minerals and water has been measured in the temperature range 100-350° for bomb runs of up to almost 2 years. Hydrogen isotope exchange between water and the clays was demonstrable at 100°. Exchange rates were 3-5 times greater for montmorillonite than for kaolinite or illite and this is attributed to the presence of interlayer water in the montmorillonite structure. Negligible oxygen isotope exchange occurred at these low temperatures. The great disparity in D and O 18 exchange rates observed in every experiment demonstrates that hydrogen isotope exchange occurred by a mechanism of proton exchange independent of the slower process of O 18 exchange. At 350° kaolinite reacted to form pyrophyllite and diaspore. This was accompanied by essentially complete D exchange but minor O 18 exchange and implies that intact structural units in the pyrophyllite were inherited from the kaolinite precursor.
A post-steam core was recovered from a Cold Lake area oil sand reservoir subjected to cyclic steam stimulation. The objective of the program war to recover competent core from a steamed portion of the reservoir and, via detailed core analysis, determine the effect of steam injection on the deteriorating productivity levels experienced at the pilot test wells.
The core was successfully retrieved by sidetracking from an existing expendable wellbore which had received four cycles of steam injection. The coring program was accomplished at a cost considerably less than that of a new well. Core recovery war satisfactory at 84%, considering the approach used.
Mineralogical analyses performed on the recovered core provided an improved understanding of the recovery mechanisms involved in steam stimulation of the reservoir, Some of the major findings were: 1. Vertical sweep efficiency was determined to be 60%. 2. Mineral reactions were confirmed and found to be a factor responsible for decreased absolute permeability. 3. The dissolution of feldspar may have contributed to suppressing the degree of swelling clay formation. 4. Thin impermeable calcite layers within the reservoir contributed to steam confinement within specific zones. These observations helped to explain the production performance recorded at the test wells and the knowledge was adapted to the development of future thermal operations at the pilot.
Introduction
Reservoir sweep efficiency is an important parameter to determine when evaluating a cyclic steam process. Conventional methods generally used to estimate sweep efficiency include observation wells, temperature logging, seismic profiling and post-recovery coring. Observation wells can be risky because they may not intersect the steamed zone. When the steam zone reaches an observation well, vertical sweep efficiency can be estimated from temperature logs run in the well, Temperature logs, however, have been shown to overestimate the thickness of the steam swept zone as a result of profile smearing(1). Seismic profiling can provide 3-dimensional seismic images which can be used to track the movement of induced heat fronts(2). This technology is relatively new and very expensive; these aspects tend to preclude its use in thermal projects. The most accurate method of determining vertical sweep efficiency is by extracting post-steam core(s) from a steamed portion of the reservoir. This is the only method that can provide tangible evidence which accurately reflects the portion of the reservoir actually swept by steam.
Another important factor associated with cyclic steam stimulation is the effect of steam injection on the mineralogy of the reservoir(3–6). Perhaps the greatest benefit of obtaining a post-steam core is the opportunity to provide unequivocal mineralogical evidence concerning the defects of steam injection on the reservoir mineralogy. Such information could also provide a valuable test for geochemical models that utilize produced fluid compositions from thermal recovery projects to monitor mineral reactions occurring in situ(7, 8).
This paper will deal with how a post-steam core program was used to provide the evidence necessary to help understand deteriorating productivity levels observed at an experimental cyclic steam pilot in the Cold Lake area of Alberta. A proprietary steam additive designed to control the swelling of smectitic clay minerals formed during steam injection was also being tested at the pilot in all attempt to limit reservoir damage that was believed to be occurring. Recovery and examination of post-steam core was necessary to confirm that reservoir damage had
The highly viscous bitumen from the Cold Lake reservoir in Alberta isproduced by the Cyclic Steam Stimulation (CSS) process. The clean oil sands ofthe Cold Lake reservoir generally produce well, but the shaley oil sands withimbedded clasts have experienced lower bitumen production and lower steaminjectivity.
This paper presents laboratory and field data that support the hypothesisthat the minerals in the clasts play a role in the production problems of theshaley oil sands. Laboratory tests reveal that clasts in the shaley oil sandshave an abundance of carbonate minerals such as siderite (iron carbonate) andaluminosilicate minerals such as kaolinite and feldspar. Laboratory studiesunder steam stimulation conditions show that the mineral reactions betweencarbonates and aluminosilicates can generate formation damaging products suchas swelling clay and carbon dioxide. Swelling clay can damage the formation byplugging the pore throats, whereas carbon dioxide can lead to near-wellborescaling. Calcium carbonate scales have been observed in downhole pumps andliners in Cold Lake wells. The field bitumen production appears to be inverselycorrelated with the carbonate content of the clasts. The field bitumenproduction is also inversely correlated with the amount of carbon dioxidegenerated in the laboratory by hydrothermal reactions of clasts. The paperdescribes the application of portable X-ray fluorescence (XRF) andnear-infrared instruments for rapid, nondestructive identification of reactiveminerals in cores, and of photoelectric absorption (Pe) logs for identifyingshaley oil sands with reactive minerals. It proposes diagnostic tests toidentify the extent and type of damage in a producing well. Finally, itdiscusses several potential methods for formation damage remediation andprevention.
Introduction
Cold Lake reservoir in northeastern Alberta has a vast resource base of oilsands. The bitumen in the oil sands has a viscosity of about 100,000 cp atreservoir temperature. Imperial Oil Resources Limited is using the Cyclic Steam Stimulation (CSS) process to recover the bitumen. The wells are drilleddirectionally from one surface location and there are twenty wells in one pad. In one cycle, steam is injected over a period of 30 to 40 days, and a hotbitumen and water mixture is produced over several months. Each well goesthrough several cycles of injection and production until steam injectionbecomes uneconomic.
A factorial design experiment was used to identify the hydrothermal reactions between the pore fluid, kaolinite, quartz and dolomite under conditions that simulate in-situ steam injection. One gram samples of kaolinite, quartz and dolomite mixed in the proportions 1:1:0.05 or 1:1:1 were reacted with 10 ml of solution at 250 °C and 300 °C for five and seven-day periods at neutral, intermediate and high pH. X-ray diffraction was used to identify the solids and inductively coupled argon plasma analysis was used to determine changes in the fluid composition.
These reconnaissance experiments showed that smectite is synthesized rapidly and is then transformed to analcime in sodic-rich alkaline solutions. Maintaining a high sodium concentration in solution and an alkaline pH appear to be the most important control in this process.
The rapid transformation of kaolinite and smectite into analcime could have a beneficial effect on permeability and recovery rates during thermal in-situ projects.
Introduction
This study was conducted to identify and examine the reactions between kaolinite, quartz and dolomite under conditions typical of in-situ steam injection. Temperatures are in the range of 200 °C to 300 °C and pressures can reach 13.8 MPa(1).
The hydrothermal reactions between kaolinite, quartz and dolomite at 25 °C to 300 °C have been discussed in several publications(2–5). These investigators have reported that clays of the smectite group are a common reaction product. Smectite is a swelling clay which can expand and/or disperse when contacted by low salinity water and contribute to formation damage via pore plugging. As little as two per cent smectite can cause a 50 fold reduction in permeability(5). The effects of smectite clays during conventional oil recovery operations have been discussed extensively in the technical literature and no attempt will be made to review them. The effects of smectite formation during thermal recovery operations are less well known although its growth has been recorded in post-steam cores(6). Young et al.(7) summarize the effects of clay formation damage in steam environment and discuss its control through clay stabilizing agents.
A factorial design was chosen for these experiments because it allows the evaluation of the combined effects of several variables in a single experiment(8,9). A maximum of four independent variables, temperature, pH, ionic composition of the pore fluid and time were in operation simultaneously during these experiments. Predicting the hydrothermal reactions in this multi-component system becomes more realistic when the interaction of several variables can be considered.
Experimental Procedures
Experimental Design
In these experiments, two of the variables were set at one of two levels: temperature 250 °C or 300 °C and duration, 5 or 7 Days. In addition, fluid composition was varied by using different quantities of NaCl, NaOH, Na2CO3, Na2B1O7, 10H2O and Na2HPO4 to adjust the salinity and pH of the starting solutions. NaOH was used to adjust the pH in most of the experiments which was set at one of three levels, neutral (pH 7), intermediate (pH 10) or high (pH 12) at room temperature, The pH at run temperature was not calculated but will be different from that at room temperature.
Most in-situ recovery processes involve heating the formation and injection of large amounts of aqueous fluids. Under these conditions, mineral reactions proceed quite readily and could cause changes in reservoir properties such as porosity and permeability.
Static autoclave experiments which simulated in-situ recovery conditions showed that dissolution of quartz kaolinite and dolomite, and formation of analcime, chlorite, smectite and calcite were the major mineral reactions that occur in Cold Lake oil sands. The process variables that influence these reactions were identified through statistical data analysis. Flow experiments with sand packs have demonstrated the possible deleterious influence of these hydrothermal reactions on permeability. The results of the tests compare favorably with published field pilot data. Formation damage by fines dispersion resulting in high residual oil saturations has been observed in medium to very fine grained sands. To an extent this formation damage can be minimized by an appropriate choice of process variables. On the other hand, maximization of fluid-rock interactions may be used to advantage in " thief" zones.
FIGURE 1. Factorial experimental design layout and sample code. The latter indicates the experimental conditions to which the samples were subjected. B = bitumen (blank if absent); b = 0.01 m borax (blank if absent); t = 200 °C; T = 250 °C; 26 = experiment duration (days); SW = 0.1 m NaCl; FW = no NaCl.
Introduction
The oil sand deposits in the province of Alberta, Canada contain a vast amount of bitumen, most of which will have to be recovered by in-situ techniques.
Many processes for secondary or tertiary recovery of conventional crude oil and for the in-situ recovery of bitumen from oil sands rely on the injection of large volumes of steam to heat the bitumen and thereby reduce its viscosity. The interaction between condensed steam and rock matrix may lead to a considerable degree of mineral dissolution, transport, precipitation and transformation(1,2,3). In turn, these reactions can cause significant changes in reservoir properties such as permeability and porosity(3,4). It has been said that steam injection leads to an acceleration of diagenesis(2). Consequently, much of the research on the relation between diagenetic characteristics and oil reservoir performance(5) is relevant to enhanced oil recovery as well as to in-situ recovery of bitumen. The experimental work for the present study consisted of three major parts:
(a) A major experimental-statistical study was undertaken to identify the most important mineral reactions that will occur at the pressures (up to 11 MPa) and temperatures (up to 325 °C) operative during in-situ recovery of bitumen by steam injection from the major Alberta oil sand deposits and to estimate the extent to which these reactions are influenced by process conditions. A factorial experimental design was used because it provides an optimum balance between the amount of information obtained and the number of experiments required(6). Also, the availability of standard computer programs for statistical analysis greatly facilitates the interpretation of the data in terms of trends and statistical significance(7).
The Lower Cretaceous (Lower Albian) Clearwater Formation at Cold Lake, Alberta is a complex assemblage of nonmarine, marginal marine and shallow marine strata. Within the study area, these strata form four unconformity-bounded depositional sequences that in most cases consists of a lower progradational unit overlain by a retrogradational unit. The base of all sequences, except the first, is marked locally by a deeply incised, northwest-south-trending paleovalley. Although eroded during a fall of relative sea level, each paleovalley was filled mostly with sediment deposited by a northwest-prograding tide-dominated delta during each subsequent rise of relative sea level. Reservoir strata occur in the lower, deltaic part of the three youngest sequences, and consist primarily of nonmarine fluvial and high-energy tidal sand flats deposits. Deltaic progradation was halted, however, by a possible decrease in sediment flux and a return to retrogressive conditions. This formed an areally extensive flooding surface, which then was overlain by retrogradational shallow-marine deposits (embayment-mouth deposits). Accordingly, each sequence represents a short-term (4th order?) fluctuation of relative sea level that was superimposed on a long-term (3rd order?) rise of relative sea level. In Addition, each successive sequence indicates a progressively more basinward migration of (tide-dominated) deltaic facies (prograding sequence set) suggestive of temporal changes in some number of local and/or regional sedimentary controls, such as sediment flux, rates of relative sea level, or depositional gradient.
Hydrogen- (δD = -106 to -97‰) and oxygen- (δ18O = +14.0 to +16.6‰) isotope compositions of kaolinite from late Cretaceous and Oligocene deposits at Iwaizumi, northeastern Japan, indicate that these clays formed by weathering of volcanic parent rocks, rather than during hydrothermal (>100 °C) alteration. The Iwaizumi kaolinites also are depleted of D and 18O relative to kaolinite formed during modern, tropical weathering, suggesting that the kaolinite developed under cool or cool-temperate conditions. The oxygen-isotope compositions of the kaolinite increase slightly upward through the deposits, perhaps implying a modest increase in temperature from late Cretaceous to Oligocene time. The δD and δ18O results for kaolinite from the Oligocene deposits closely follow the kaolinite weathering line. However, a small but systematic deviation from this line for the Cretaceous kaolinites is most simply explained by post-formational, hydrogen-isotope exchange between these clays and downward percolating meteoric water.
O-isotope analysis of shales sampled from wells drilled through sedimentary deposits in the Gulf of Mexico region indicates that the sediments and rocks are not isotopically equilibrated systems - even those that have been buried to depths where temperatures are as high as 170 °C. In comparison with the coarser fractions, the finer fractions of both clay minerals and quartz are almost always richer in O18. O-isotope disequilibrium among the clay fractions becomes less marked as burial temperature increases. O-isotope exchange between clay and pore water become more extensive at higher temperatures; this corresponds to more extensive diagenetic alteration of mixed-layer illite-smectite. There is no evidence for O-isotope exchange between detrital quartz and pore water. However, quartz that forms diagenetically as an accompaniment to the conversion of smectite to illite layers in the mixed-layer clay forms in equilibrium with the pore water. The usefulness of O-isotope geothermometry for determination of the maximum temperatures to which shales have been heated during burial was investigated. Temperatures were calculated from the O-isotope fractionations between coexisting fine-grained quartz and clay from three wells; these calculated temperatures progressively approached the measured well (logged) temperatures as depth of burial and temperature increased. In one well, good agreement between calculated and measured temperatures was obtained for measured temperatures between 100 and 180 °C. In two other wells, satisfactory agreement was approached but not obtained at measured temperatures as high as 120 °C. Temperatures calculated from the O-isotope fractionations of quartz and calcite or calcite and clay were not reasonable. This probably reflects isotope exchange between calcite and pore water after the silicates attained their measured isotope ratios. Consequently, calcite is not a suitable mineral for use in isotope geothermometry of diagenetically altered shales.
Carbon dioxide, produced at low temperatures, is the dominant gaseous species evolved during steam-assisted thermal recovery of bitumen at the Tucker Lake pilot, Cold Lake, Alberta. Two possible sources for the produced COâ are considered: pyrolysis of bitumen and dissolution of carbonate minerals. Data from natural systems and experiments by other authors suggest that clay-carbonate reactions are the dominant source of COâ. Bitumen pyrolysis may contribute small amounts of COâ, probably by decarboxylation, early in the production cycle but cannot contribute significant volumes. The recognition of production of COâ by reactive calcite destruction at temperatures between 70 and 220°C suggests that this process may be responsible for the production of large quantities of COâ in natural systems, particularly in lithofeldspathic sands and shales with high carbonate content and abundant clays. Organic acids have been suggested to be the source of COâ in diagenetic fluids, but the results presented here suggest that this hypothesis requires more complete investigation.
Solution-mineral equilibria were calculated for the aqueous phase, and X-ray diffractograms obtained for the solids, from the factorial experiment reported in Part I of this series of papers, in which a shale from the Lower Cretaceous McMurray Formation in the Athabasca oil sand deposit of Alberta, in the presence or absence of bitumen, was subjected to hydrothermal treatment with aqueous fluids of varying pH and salinity, at two different temperatures, for periods up to 92 hours. Data representing the departures from equilibrium, and normalized X-ray diffraction peak intensities, were studied by statistical analysis of variance. In addition to the dissolution of quartz, montmorillonite was formed probably through a transitional illite-montmorillonite interstratined layer structure, with the reaction being favored by high pH of the aqueous phase. The dissolution of siderite is significantly affected by time, salinity, and the interactions between pH and salinity, time and salinity, and pH, temperature and time. Despite the restrictions imposed by a laboratory investigation, the results demonstrate that mineral dissolution and transformation will be extensive during in situ recovery operations in oil sand deposits.
The δD and δ18O values of diagenetic kaolinite and 10Åclay minerals (illite, illite/smectite) have been determined for Lower Cretaceous Viking Formation marine sandstones and conglomerates, Upper Cretaceous basal Belly River Group shoreline and deltaic sandstones, and overlying Belly River/Brazeau Groups continental sandstones from the western Canada sedimentary basin. Early and late diagenetic kaolinites have a remarkably small range of δD values (−132 to − 112%, Viking Formation; −137 to−128%, Belly River/Brazeau Groups) relative to their δD18O compositions (+13.8 to +26.9%, Viking Formation; +5.9 to +12.7%, Belly River/Brazeau Groups). The δD values are also much lower than commonly reported for kaolinite.
Cyclic Steam Stimulation (CSS) has been a commercial recovery process since the mid 1980s in the Cold Lake area in northeast Alberta. The current bitumen production is over 220,000 B/D using CSS from this area. To achieve desired injectivity in the bitumen saturated reservoir, steam is usually injected at a pressure above or close to the fracture pressure of the formation. A relatively high pressure drawdown is created between the wellbore and formation during the production phase, particularly in the early stage of the production cycle where formation compaction and solution gas drive are the two most important recovery mechanisms. The CSS process has limited application in reservoirs with thick bottom water or in reservoirs with fine grain sands.
The Steam Assisted Gravity Drainage (SAGD) process has been field tested and commercially expanded in the Lower Grand Rapids and Clearwater Formations in the Cold Lake area. In contrast to CSS, SAGD is a continuous steam injection process that relies on gravity and requires a minimum pressure drawdown to drive the reservoir fluids to the wellbore. This provides a significant advantage for SAGD as an option for the reservoirs with bottom water, top gas or with formations with fine grain sands. Several SAGD projects are in operation in different types of reservoirs in the Cold Lake and Lloydminster areas; some with thick bottom water zones.
A performance review is conducted based on the available data for various CSS and SAGD projects in the Cold Lake area. The selection criteria between CSS and SAGD technologies for Clearwater and Lower Grand Rapids are discussed. Reservoir modeling results are presented concerning the impact of well placement, reservoir heterogeneity and operating parameters on SAGD performance, based on Osum's Lower Grand Rapids and Clearwater geology in the Cold Lake area.
Mineralogical and hydrogen isotopic studies have been made on clay minerals occurring in the Ohnuma geothermal area, northeastern Japan. Here, clay minerals such as smectite, kaolinite, dickite, sericite, and chlorite were formed by hydrothermal alteration of Miocene rocks. A chemical equilibrium can be assumed to be attained from the fact that the amount of expandable layer in the interstratified chlorite/smectite decreases and the polytype of sericite changes from 1M to 2M1 with increasing depth and temperature. The hydrogen isotopic composition (D/H) of the clay minerals is lighter than that of the geothermal and local meteoric waters by about 20-400/00. The hydrogen isotopic fractionation factors alphamineral-water are as follows: 0.972-0.985 for kaolinite and dickite, 0.973-0.977 for sericite, and 0.954-0.987 for chlorite. In the temperature range from 100 to 250°C, the hydrogen isotopic fractionation factors between these minerals and water are not sensitive to the temperature. alphachlorite-water depends on the kind of octahedrally coordinated cations which lie close to the hydroxyl groups; it becomes large with an increase of Mg content of chlorite.
The reactions between silicates and carbonates were experimentally simulated at conditions similar to thermal recovery of oil from oil sands. Several important observations are: (1) in general, smectite forms from silicate-carbonate reactions in fresh water or in dilute Na-bearing fluids. For this reaction silicate can be kaolinite, feldspar or volvanic glass whereas carbonate can be dolomite, calcite, ankerite or siderite; (2) analcime instead of smectite forms in fluids with higher [Na+] or pH; (3) illite or mixed-layered illite-smectites form in the prescnce of [K+] and NH4-zeolites and NH4-illite form in the presence of NH4+; (4) Ca-mica(margarite) forms from calcite and kaolinite with high fluid/rock ratio (200:1); (5) talc forms from dolomite and silica in fresh water; (6) chlorite forms from kaolinite and dolomite in runs with low fluid/rock ratio; (7) the reaction temperature significantly increases with increasing CO2/H2O ratio in the fluid; and (8) the reaction rate decreases as the PCO2 in the system increase but increases again to the initial reaction rate as CO2 is released from the reaction vessel.The simulations show that mineralogy, injection fluid composition and flow rate (fluid/rock ratio) are key factors that control formation damage during steam flooding. The phase relatioships and kinetic data suggest that formation damage during steam treatment may be prevented or retarded by maintaining high XCO2 in the reservoir. The results are useful for improving the efficiency of thermal recovery.
A 1-10 mg portion of water is reduced with Zn metal in a sealed tube at 450 °C to prepare hydrogen for isotopic analysis. After reaction the tube is attached directly to the mass spectrometer without further processing. Replicate analyses of water samples give reproducibility of 0.2-0.4% (1sigma); fluid inclusion samples, 1.9%; and water of hydration of gypsum, released and reduced in the sealed tube, 1.1%. A batch of 10 samples can be prepared in 1 h.
Semiquantitative mineral analysis has been done by X-ray diffraction on the < 2 μ- and 2-20 μ-size fractions of approximately five hundred Recent deep-sea core samples from the Atlantic, Antarctic, western Indian Oceans, and adjacent seas. Relative abundances of montmorillonite, illite, kaolinite, chlorite, gibbsite, quartz, amphibole, clinoptilolite-heulandite(?), and pyrophyllite(?) were determined. Mixed-layer clay minerals, feldspars, and dolomite were also observed but not quantitatively evaluated. From the patterns of mineral distribution, the following conclusions appear warranted: Most Recent Atlantic Ocean deep-sea clay is detritus from the continents. The formation of minerals in situ on the ocean bottom is relatively unimportant in the Atlantic but may be significant in parts of the southwestern Indian Ocean. Mineralogical analysis of the fine fraction of Atlantic Ocean deep-sea sediments is a useful indicator of sediment provenance. Kaolinite, gibbsite, pyrophyllite, mixed-layer minerals, and chlorite contribute the most unequivocal provenance information because they have relatively restricted loci of continental origin. Topographic control over mineral distribution by the Mid-Atlantic Ridge in the North Atlantic Ocean precludes significant eolian transport by the jet stream and emphasizes the importance of transport to and within that part of the deep-sea by processes operative at or near the sediment-water interface. Transport of continent-derived sediment to the equatorial Atlantic is primarily by rivers draining from South America and by rivers and wind from Africa. The higher proportion of kaolinite and gibbsite in deep-sea sediments adjacent to small tropical South American rivers reflects a greater intensity of lateritic weathering than is observed near the mouths of the larger rivers. This may be explained by a greater variety of pedogenic conditions in the larger drainage basins, resulting in an assemblage with proportionately less lateritic material in the detritus transported by the larger rivers despite their quantitatively greater influence on deep-sea sediment accumulation. In the South Atlantic Ocean, the fine-fraction mineral assemblage of surface sediment in the Argentine Basin is sufficiently unlike that adjacent to the mouth of the Rio de la Plata to preclude it as a major Recent sediment source for that basin. The southern Argentine Continental Shelf, the Scotia Ridge, and the Weddell Sea arc mineralogically more likely immediate sources. Transport from the Weddell Sea by the Antarctic Bottom Water may be responsible for the northward transport of fine-fraction sediment along parts of the western South Atlantic as far north as the Equator.
X-ray diffraction analysis, thin section analysis and scanning electron microscopy were used to compare the mineralogy of pre- and post-recovery cores from the Lower Cretaceous Sparky interval in Aberfeldy steamflood and fireflood pilot projects. Lloydminster area, Saskatchewan, Canada. The objectives were to document the potential changes in mineralogy that may occur during recovery of heavy oil and to evaluate the risk of formation damage from mineral reactions.These unconsolidated sediments are very quartzose (90%) and they also contain feldspars, clays (mainly kaolinite) and carbonate cements (siderite and ankerite). The formation of new minerals in the burned zone and the plugging of pores by coke in the zones below the burned zones is likely to cause small reductions in porosity and permeability. Illite formation is observed in the steamflood pilot but is not extensive enough to cause formation damage. Carbonate scale is observed at the producing wells.During steamflooding illite and chlorite are formed; the smectite which is observed is due to mud invasion. During fireflooding, illite forms in the coked zones, whereas K-feldspar and hematite form in the burned zones. Thermodynamic calculations of the stability of mineral-forming reactions are in agreement with physical conditions during steaming. The decomposition of kaolinite in the burned zones indicates combustion temperatures greater than 510–540°C. It may be concluded that in a period of a few years only minor detrimental effects related to mineralogy occurred during thermal recovery in the Aberfeldy pilot projects.
Hydrogen isotope fractionation factors between hydroxyl-bearing minerals and water were determined at temperatures ranging between 400 and 850°C. The hydrogen isotope exchange rates for the mineral-water pairs examined were very slow. In most cases it was necessary to use an interpolation method for the determination of the hydrogen isotope equilibrium fractionation factor, α_e.
For the temperature range of 450–850°C the hydrogen isotope fractionation factors for the mica-water and amphibole-water systems are simply expressed as a function of temperature and the molar fractions of the six-fold coordinated cations in the crystal, regardless of mineral species, as follows: 10^3 In α_(e(mineral-water)) = − 22.4 (10^6T^(−2)) + 28.2 + (2X_(Al) − 4X_(Mg) − 68X_(Fe)), where X is the molar fraction of the cations. As the equation indicates, for any specific composition of the OH-bearing minerals, the change of α_e with temperature, over the temperature range investigated, is the same for all minerals studied. Thus for any specified values of X_(Al), X_(Mg), and X_(Fe) for these minerals, the relationship between α_e and T is 10^3 In α_e = αT^(−2) + k. Consequently, hydrogen isotope fractionation among coexisting minerals is temperature independent and cannot be used as a hydrogen isotope geothermometer.
Some exceptions to the above general observations exist for minerals such as boehmite and kaolinite. In these minerals hydrogen bonding modifies the equilibrium hydrogen isotopic fractionation between mineral and water.
Miocene submarine to Quaternary terrestrial volcanism in southwestern Hokkaido, Japan, is associated with hydrothermal clay alteration and mineralization, including Kuroko-type deposits at Kagenosawa (14.2 Ma, Cu > Zn, Pb > Au) and Minamishiraoi (12.5 Ma, Ba > Zn, Pb, Cu), vein-style mineralization at Date (5.2 Ma, Au-Ag-Cu-Pb-Zn) and Chitose (3.6 Ma, Au-Ag), and geothermal activity at Noboribetsu (≤1.8 Ma). The δD and δ¹⁸O values of mica (sericite), mica-smectite, chlorite, chlorite-smectite, nacrite, dickite, kaolinite, and smectite were used to deduce the type(s) of hydrothermal fluid at each locality. Calculated compositions for Minamishiraoi and Kagenosawa fluids suggest that seawater was dominant, but some mixing with magmatic water is also indicated, particularly for the polymetallic Kagenosawa deposit. Hydrothermal fluids at Date, Chitose, and the Noboribetsu geothermal area were dominated by meteoric water. Minor involvement of magmatic water during mineralization at Date cannot be ruled out, but evolution of local meteoric water along an evaporation trend and/or an ¹⁸O-shift due to hydrothermal rock-meteoric water interaction also could have produced appropriate fluid compositions. The δD and δ¹⁸O values of modern hot-spring waters at Noboribetsu closely parallel fluid compositions calculated for the clay alteration at Date, Chitose, and Noboribetsu.
δD values of water samples from two Gulf Coast geopressured fields vary linearly with temperature, while the δD values from the coexisting clays remain constant and are independent of temperature. Fluid How rates on the order of millimeters per year, characteristic of Gulf Coast geopressured systems, provide adequate residence time for hydrogen isotope equilibrium to be achieved between the extant porewaters and clay minerals. Since equilibrium is achieved, these δD values are used to calculate the temperature dependence of the hydrogen isotope fractionation factor between illite-smectite and water, αclay-waterH, between 0 and 150°C: . This equation predicts values for αclay-waterH at 96°C which are equal to those predicted by a similar equation derived by Yeh (1980). Above and below 96°C, this new equation predicts values which diverge from those predicted by the equation of Yeh (1980) with a difference of +9 at 150°C and −25 at 0°C. The possibility is raised that the very slow upward component of flow characteristic of Gulf Coast geopressured sediments, combined with the slow downward subsidence of the clay-rich sediments, can result in a system which is rock-dominated with respect to hydrogen.
The D/H ratios and water contents in fresh submarine basalts from the Mid-Atlantic Ridge, the East Pacific Rise, and Hawaii indicate that the primary D/H ratios of many submarine lavas have been altered by processes including (1) outgassing, (2) addition of seawater at magmatic temperature, and (3) low-temperature hydration of glass. Decreases in δD and H2O+ from exteriors to interiors of pillows are explained by outgassing of water whereas inverse relations between δD and H2O+ in basalts from the Galapagos Rise and the FAMOUS Area are attributed to outgassing of CH4 and H2. A good correlation between δD values and H2O is observed in a suite of submarine tholeiites dredged from the Kilauea East Rift Zone where seawater (added directly to the magma), affected only the isotopic compositions of hydrogen and argon. Analyses of some glassy rims indicate that the outer millimeter of the glass can undergo lowtemperature hydration by hydroxyl groups having δD values as low as −100.δD values vary with H2O contents of subaerial transitional basalts from Molokai, Hawaii, and subaerial alkali basalts from the Society Islands, indicating that the primary δD values were similar to those of submarine lavas.Extrapolations to possible unaltered δD values and H2O contents indicate that the primary δD values of most thoteiite and alkali basalts are near −80 ± 5: the weight percentages of water are variable, 0.15–0.35 for MOR tholeiites, about 0.25 for Hawaiian tholeiites, and up to 1.1 for alkali basalts. The primary δD values of −80 for most basalts are comparable to those measured for deep-seated phlogopites. These results indicate that hydrogen, in marked contrast to other elements such as Sr, Nd, Pb, and O, has a uniform isotopic composition in the mantle. This uniformity is best explained by the presence of a homogeneous reservoir of hydrogen that has existed in the mantle since the very early history of the Earth.
Oxygen and hydrogen isotope analyses have been made on a variety of clay minerals of sedimentary and diagenetic origins. The interlayer water of clay minerals was found to exchange rapidly with atmospheric water. Conditions under which the interlayer water could be removed from the clays without affecting the isotopic compositions of their aluminosilicate oxygen and hydrogen were therefore determined, and the interlayer water was routinely removed and discarded prior to isotopic analysis.Approximate fractionation factors for clay mineral-water systems at sedimentary temperatures, inferred from the isotopic compositions of natural samples, are: αOxygenmin-H2OαHydrogenmin-H2O Montmorillonite 1.027 0.94 Kaolinite 1.027 0.97 Glauconite 1.026 0.93Consistency of a relationship between oxygen and hydrogen isotope ratios of kaolinites taken from a variety of areas and having different isotope ratios was demonstrated. This relationship results from exchange of clays with different meteoric waters under conditions in which the fractionation factors are relatively constant. This strongly suggests that the fractionation factors are equilibrium ones and that kaolinite forms in isotopic equilibrium with its environment. Deviations of the isotopic composition of montmorillonites from a similar relationship have been interpreted as resulting from isotopic exchange at slightly elevated temperatures. There was no clearly demonstrable case of clay minerals undergoing isotopic re-equilibration at sedimentary temperatures, although this is one possible interpretation of the data of some Upper Cretaceous glauconites.
The experimental procedure for the extraction of hydrogen from natural hydrous silicate minerals is outlined. The D/H ratios, water, and flourine contents have been determined for coexisting biotite, hornblende, and chlorite from rocks of the east-central Sierra Nevada and Yosemite National Park regions. These data are discussed in relation to the petrogenesis of the principal rock types of the regions. Local hydrogen isotopic fractionation and equilibrium between coexisting hydrous silicates were noted.
Depleted δ18O- and δD-values of +6.1 to +9.4‰ and −107 to −94‰, respectively, have been obtained from kaolinite samples of early Permian (Sakmarian-Artinskian) age from the Gunnedah Basin, eastern Australia.The samples come from kaolinite clayrocks representing both in situ kaolinitic weathering profiles and the eroded and re-deposited products of this weathering developed in the Quirindi-Wingen and Boggabri-Gunnedah areas of New South Wales, Australia. The clayrocks were produced by the intense surficial weathering of an underlying volcanic sequence, with subsequent erosion and re-deposition in basins flanking the volcanic pile.The calculated isotopic composition of meteoric water in equilibrium with kaolinite from the clayrocks had δ18O of ⩽ −17‰ and δD of ⩽ −125‰, indicating polar or sub-polar temperatures of condensation. As kaolinite formation cannot occur below the freezing point of water, the highly depleted isotopic results obtained from the samples suggest equilibrium with waters partly derived from deglaciation of the Gondwanan landmass, an event which consequently must have been well underway in eastern Australia by the Sakmarian-Artinskian.The climate prevailing at the time of kaolinite formation is unlikely to have been warmer than cool temperate, a conclusion which is difficult to reconcile with the classical interpretation of kaolinitic weathering as a tropical or subtropical phenomenon. This suggests that high rates of infiltration, efficient leaching of soluble cations, and good drainage are of more importance to kaolinite formation than the temperature at which the process operates.Oxygen-isotope exchange in the kaolinite samples since formation is thought to have been negligible, however, marked post-formational hydrogen-isotope exchange is demonstrable at temperatures not exceeding ∼ 80°C and probably considerably lower in some cases.
A detailed, systematic experimental and theoretical study was conducted to investigate the effect of pressure on equilibrium D/H fractionation between brucite (Mg(OH)2) and water at temperatures from 200 to 600°C and pressures up to 800 MPa. A fine-grained brucite was isotopically exchanged with excess amounts of water, and equilibrium D/H fractionation factors were calculated by means of the partial isotope exchange method. Our experiments unambiguously demonstrated that the D/H fractionation factor between brucite and water increased by 4.4 to 12.4‰ with increasing pressure to 300 or 800 MPa at all the temperatures investigated. The observed increases are linear with the density of water under experimental conditions. We calculated the pressure effects on the reduced partition function ratios (β-factor) of brucite (300–800 K and P ≤ 800 MPa) and water (400–600°C and P ≤ 100 MPa), employing a statistical-mechanical method similar to that developed by Kieffer (1982) and a simple thermodynamic method based on the molar volumes of normal and heavy waters, respectively. Our theoretical calculations showed that the reduced partition function ratio of brucite increases linearly with pressure at a given temperature (as much as 12.6‰ at 300 K and 800 MPa). The magnitude of the pressure effects rapidly decreases with increasing temperature. On the other hand, the β-factor of water decreases 4 to 5‰ with increasing pressure to 100 MPa at 400 to 600°C. Overall D/H isotope pressure effects combined from the separate calculations on brucite and water are in excellent agreement with the experimental results under the same temperature-pressure range. Our calculations also suggest that under the current experimental conditions, the magnitude of the isotope pressure effects is much larger on water than brucite. Thus, the observed pressure effects on D/H fractionation are common to other systems involving water. It is very likely that under some geologic conditions, pressure is an important variable in controlling D/H partitioning.
The equilibrium hydrogen isotope fractionation factor (α) between kaolinite and water in the temperature range 330 to 0°C is 1000 In αkaol-water = −2.2 × 106T−2 − 7.7. This monotonic expression is based on a combination of experimental data with >75% of exchange and empirical calibrations. The previously proposed and widely accepted complex fractionation expression is considered to reflect the role of surface and intersite fractionation effects in the low percent of exchange experiments(Liu and Epstein, 1984), and incorrect δD water values for the empirical values (Lambert and Epstein, 1980). There is no measurable fractionation between dickite and kaolinite. The temperature dependence of the kaolinite-water hydrogen isotope fractionation factor can probably be used as a model for other phyllosilicate-water systems below 350°C.