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An overview of Triassic stratigraphy and depositional environments in the Rocky Mountain Foothills and Western Interior plains, Peace River Arch area, northeastern British Columbia
Abstract
Triassic rocks in the Peace River Arch area comprise over 1200 m of westward-thickening sediments. Faunas range in age from Griesbachian to Norian. In the outcrop belt of the Foothills between Sukunka and Pine rivers and Williston Lake, the succession is subdivided into eight formations. Exposures south of the Sukunka-Pine River area are divided into two formations. In the subsurface of the eastern Foothills and western Plains, Triassic rocks are subdivided into six formations. During Triassic time, the former Peace River Arch remained basinal, with the axis area characterized by local movement along former Paleozoic horst and graben faults. The strata were deposited during three regional transgressive regressive cycles in a cratonic embayment of a continental shelf and shoreline, along the passive western margin of the North American Craton. -from Authors
... The northwestern area of Montney Formation in British Columbia is dominance of siltstone. This Montney Formation is generally thickening westward and deepening [16,[18][19][20][21][22][23]. Within these areas, the desorbed gas volume relatively increased westward, following the general distribution of the formation. ...
... The Montney Formation was deposited during the lower Triassic time (during approximately 252 to 247 Ma; million years ago) within the Western Canada Sedimentary Basin (WCSB), ca 750,000 km 2 in areas, equivalent to presentday subsurface of northeastern British Columbia and western Alberta, of Peace River subbasin ( Figure 2). Its average thickness is 100-300 m, and its burial depth reaches maximum up to 4 km in westward [18][19][20][21][22][23]. The Montney Formation is mainly composed of dolomitic siltstone, very fine to fine grain sandstone and silty shale [16,18,22,23]. ...
... Its average thickness is 100-300 m, and its burial depth reaches maximum up to 4 km in westward [18][19][20][21][22][23]. The Montney Formation is mainly composed of dolomitic siltstone, very fine to fine grain sandstone and silty shale [16,18,22,23]. The formation is divided into lower and upper members ( Figure 3) [11,18,19,25]. ...
Shale reservoir has been focused among unconventional resources since the first extraction of free and adsorbed gas from the low-permeable Barnett Shale via horizontal drilling and hydraulic fracturing. In the beginning of production, free gas was rapidly recovered through an artificial fracture system, and then, desorbed gas followed at the final stage due to a decrease of reservoir pressure. This desorbed gas volume commonly occupies 10 to 40% of total gas production in shale gas play although it shows wide variety in cumulative gas volume and production time. The largest gas production in Canada is recovered from either tight sandstone or shale reservoirs. The Montney play in Western Canadian Sedimentary Basin (WCSB) has produced up to 80% of Canadian natural gas production. The desorbed gas production from this play has been reported up to 10% of total produced gas. The distribution and productivity of the desorbed gas have not been fully studied. Therefore, we focus to understand the distribution of the desorbed gas volume of eastern, middle, and northwestern areas in the Montney play. The desorbed gas volume within these areas was estimated from the relationship among canister, illite, and shale volumes in core samples and well logs. The average shale volume fraction in eastern area is 0.38 , the average illite mineral volume fraction is 0.25 , and the average desorbed gas volume refers to 8.52 scf/ton. In middle area, calculated volume represents 0.34 , 0.216 , and 8.15 scf/ton as listed above. The northwestern area also shows 0.65 , 0.4 , and 9.78 scf/ton, respectively. 3D models of each area indicated relatively rich and lack parts of desorbed gas volume. These estimated desorbed gas volume and gas production history were compared in order to understand when and how the desorbed gas would affect to gas production. It shows strong positive relationship, gradually increasing correlation to the later stage (from 24-44 months to 36-44 months) of gas production in the entire areas. This result implies that the estimation of later stage gas productivity is able from the estimated volume of desorbed gas, and also, the total gas production can be forecast in shale gas reservoir. Northwestern area in Montney play preserves relatively abundant desorbed gas volume, which will be dominant after 24 months of production.
1. Introduction
The shale gas production within Western Canadian Sedimentary Basin (WCSB), Alberta, and British Columbia province, occupies about 80 percent of Canadian natural gas production. The gas productions in Alberta and British Columbia provinces will increase until 2036 up to 14,000 and 9,000 mmcf/day, respectively [1]. Growing attention of shale gas play in WCSB leads to understand characteristics of shale formation such as sedimentary features, petrophysical properties (porosity, permeability, saturation, brittleness, etc.), and gas production profile (free and desorbed) [2–10]. The production of the desorbed gas, also known as the residual gas, is dominant at the final stage after the most of free gas was already extracted. However, it is still unknown that when and how the production of in situ desorbed gas would affect the overall gas production (Figure 1). Even though these gas volume commonly occupies 10 to 40% of total gas production in shale gas play [8, 11].
(a)
... The Montney was named by Armitage (1962) and was defined as an argillaceous siltstone unit. The base of the Montney was placed at the top of the Paleozoic and the contact between the Montney and the overlying Doig Formation was placed at the base of the prominent phosphate bed, which is marked by a high spike on the gamma curve (Armitage, 1962 (Gibson and Barclay, 1989;Gibson and Edwards, 1990). ...
... Montney sediments consist predominantly of dark grey, calcareous and dolomitic siltstones and minor shales. They have been interpreted as a mid-to distal shelf and/or slope environment (Gibson and Edwards, 1990). arid, continental ones that pushed the warmer ocean waters further out to sea and allowed for cold, anoxic upwellings to take place along the coast (Vincent, 1986;Davies, 1997a). ...
... Grain size tends to increase towards the east (Gibson and Edwards, 1990;Edwards et al., 1994). Davies et al. (1997a) recently re-evaluated the sedimentology of the Montney. ...
Some geomechanical properties of the Montney shale were investigated experimentally in this study. From the Brazilian and point load strength tests, the tensile strength in the horizontal direction was dominated by the bond strength of the intact structure (6-15.3 MPa), whereas that in the vertical direction was controlled by the existing natural beddings (0.7-2.8 MPa). Compressive strength, compressive elastic modulus in the vertical direction and the Poisson‟s ratio were measured from the unconfined compressive strength test as 99 MPa, 25 GPa, and 0.1, respectively. Tensile and compressive elastic moduli in the horizontal direction were measured from Brazilian test as 31 GPa and 40 GPa, respectively. From the shear test results, the cohesion was found as 2 MPa and the peak friction angle was about 40o. From this study it was found that the pre-existing planes of weakness play a major role in failure and anisotropic behavior of the Montney shale.
... Dans la region de la riviere de la Paix, les couches affleurantes et enfouies font partie des coupes de reference les plus completes du Trias de la Cordillere canadienne. La stratigraphie et le style structural de cette region ont ete decrits par Gibson et Barclay (1989), Gibson et Edwards (1990), Gibson (1990Gibson ( , 1992aGibson ( , b, 1993 et Thompson (1989). Un excellente controle biostratigraphique a ete etabli a partir d 'etudes sur les conodontes, les ammonoi"des et les bivalves (Orchard, 1983(Orchard, , 1991Tozer, 1961Tozer, , 1963Tozer, , 1965Tozer, , 1979Tozer, , 1982aTozer, , 1994 Near the base of the S. incrementum ichthyolith Zone in the Lower Norian, S. incrementum n. sp., Suaviloquentia longilingua n. sp. ...
... Dans la region de la riviere de la Paix, les couches affleurantes et enfouies font partie des coupes de reference les plus completes du Trias de la Cordillere canadienne. La stratigraphie et le style structural de cette region ont ete decrits par Gibson et Barclay (1989), Gibson et Edwards (1990), Gibson (1990Gibson ( , 1992aGibson ( , b, 1993 et Thompson (1989). Un excellente controle biostratigraphique a ete etabli a partir d 'etudes sur les conodontes, les ammonoi"des et les bivalves (Orchard, 1983(Orchard, , 1991Tozer, 1961Tozer, , 1963Tozer, , 1965Tozer, , 1979Tozer, , 1982aTozer, , 1994 Near the base of the S. incrementum ichthyolith Zone in the Lower Norian, S. incrementum n. sp., Suaviloquentia longilingua n. sp. ...
... The position of samples within these zones and stratigraphic correlation of the sections are shown in Figure 2 (in pocket). McLearn (1960), Gibson (1990Gibson ( , 1992aGibson ( , 1993, and Gibson and Edwards (1990), describe the lithology of strata at most of these localities. A locality register and detailed sample information are included in Appendices 1 and 2. ...
Diverse and abundant Middle and Late Triassic elasmobranch ichthyoliths (microscopic shark teeth and scales) coexisting with conodonts, ammonoids, and bivalves were recovered from carbonates of the Pardonet, Baldonnel, Ludington, and Liard formations in the Peace River area of British Columbia. These faunas provide an excellent biostratigraphical framework for Triassic strata. Results from this study demonstrate that ichthyoliths can be used in basin analyses to date and correlate strata. The following summarizes the main achievements of this project. 1) Systematic description and illustration of Triassic elasmobranch ichthyoliths include seven species of teeth and ninetten new form general and fifty-three new form species of scales. 2) Ichthyolith distributions consist of distinct faunal assemblages for the Kadinian, Upper Carnian, and Middle Norian. The Carnian/Morian, boundary is marked by the disappearance of many Ladinian and Carnian elasmobranch species. In the Middle Norian, elasmobranch faunas reached a new peak of diversity and abundance. 3) A provisional ichthyolith zonation for the Middle and Upper Triassic is proposed for the Peace River area. The sequence of coeval conodonts and(or) ammonoids indicate tha tthe Coniunctio aequirugosa ichthyolityh zone is Ladinian, the Synechodus multinodosus ichthyolith Zone is Upper Carnian, and the Synechodus incrementum ichthyolith Zone is Lower and Middle Norian. 4) New approaches to ichthyolith identification include recognizing diagnostic characteristics of scale and tooth bases, and using binomial, form, and utilarian taxonomic systems. 5) Interpretations of histological and moprhological features of elasomobranch teeth suggest that more derived neoselachian species than were originally known are present in the Triassic.
... The base of the Montney Formation is placed at the top of the Paleozoic, overlying an erosional unconformity on Permian strata of the Belloy Formation; in other areas within the basin, the basal contact is conformable or corresponds to an unconformity along Carboniferous strata of the DeBolt Formation (Zonneveld et al., 2010a;Zonneveld and Moslow, 2018). The top of the Montney Formation is typically an erosional boundary demarcated by the Glossifungites Ichnofacies, and/or a phosphatic conglomerate lag overlain by the Sunset Prairie Formation or Doig Formation ( Fig. 1; Armitage, 1962;Gibson and Edwards, 1990;Moslow and Davies, 1997;Furlong et al., 2018aFurlong et al., , 2018b; toward the east, the Montney Formation is erosionally overlain by Lower Cretaceous strata of the Bluesky Formation (Zonneveld et al., 2010b). In the subsurface of northeastern British Columbia, the Montney is laterally equivalent to outcrop of the Grayling and Toad formations, and the Vega and Phroso members of the Sulphur Mountain Formation, in the northern and southern Rocky Mountain Foothills and Front Ranges ( Fig. 1; Gibson and Edwards, 1990;Edwards et al., 1994;Zonneveld et al., 2010a). ...
... The top of the Montney Formation is typically an erosional boundary demarcated by the Glossifungites Ichnofacies, and/or a phosphatic conglomerate lag overlain by the Sunset Prairie Formation or Doig Formation ( Fig. 1; Armitage, 1962;Gibson and Edwards, 1990;Moslow and Davies, 1997;Furlong et al., 2018aFurlong et al., , 2018b; toward the east, the Montney Formation is erosionally overlain by Lower Cretaceous strata of the Bluesky Formation (Zonneveld et al., 2010b). In the subsurface of northeastern British Columbia, the Montney is laterally equivalent to outcrop of the Grayling and Toad formations, and the Vega and Phroso members of the Sulphur Mountain Formation, in the northern and southern Rocky Mountain Foothills and Front Ranges ( Fig. 1; Gibson and Edwards, 1990;Edwards et al., 1994;Zonneveld et al., 2010a). ...
Hydrocarbon production from the Lower Triassic Montney Formation in northeastern British Columbia, occurs primarily from unconventional reservoirs consisting predominantly of fine-to coarse-grained siltstone beds. In this area, the lithostratigraphy of the formation is difficult to characterize due to the complexities associated with subtle grain-size variation, diminutive biogenic structures, lateral facies variability, and distribution of local discontinuities. Detailed sedimentologic and stratigraphic analyses are essential for understanding and refining the depositional models and stratigraphic framework of the Montney Formation. Based on detailed core examination focused on sedimentological, paleontological and ichnological characteristics, eleven lithofacies and three recurring facies associations are identified within the Lower Triassic Montney Formation in northeastern British Columbia. The lithofacies identified are interpreted to have been deposited in offshore, offshore transition and lower shoreface settings, along a storm-dominated mixed siliciclastic-carbonate ramp. Facies associations include FA(A): siliciclastic distal offshore transition to distal offshore; FA(B): mixed siliciclastic carbonate, storm-influenced offshore to offshore transition; and FA(C): storm-dominated siliciclastic offshore transition to lower shoreface. Trace fossil assemblages correspond to a stressed Cruziana Ichnofacies, and are overall characterized by low diversity (1–6 ichnogenera), small size trace fossils (1–12 mm in diameter), and variable bioturbation intensity (0–6). The vertical variation in SDI values reflect changes in physico-chemical conditions during deposition of the Montney Formation, particularly across the Smithian-Spathian boundary. Understanding the lateral-facies variability and overall stratigraphic architecture of the Montney Formation in northeastern BC, constitute key elements in defining and correlating existing and new potential hydrocarbon reservoirs in the area.
... Davies et al., 1997;Orchard and Zonneveld, 2009;Crombez et al., 2016;Davies et al., 2008;Proverbs et al., 2018;Zonneveld and Moslow., 2018). The Montney unconformably overlies the Permian Belloy Formation and is truncated from above by the Coplin and sub-Jurassic unconformities (Gibson and Edwards, 1990;Edwards et al., 1994;Davies et al., 1997;Moslow 2000) (Figure 2). ...
... The mineralogical assembly in the Monteney Formation consists of quartz, feldspars, micas, calcite, dolomite, iron-dolomite, low expandability mixed-layer illite smectite clays (MLIS), and pyrite, with minor amounts of apatite, barite, kaolinite, chlorite, and heavy minerals Barber, 2003;Derder, 2012;Playter, 2013;Crombez, 2016;Vaisblat et al.,2016). Grain size in the Montney Formation varies from very fine sand to clay-size material, with a slight increase in grain size (to fine sand) toward the eastern margins of the formation (Gibson and Edwards, 1990;Edwards et al., 1994;Davies et al., 1997;Zonneveld et al., 2011;Vaisblat et al., 2016). The main control over rock composition is diagenetic, with early extensive cements accounting on average for a third of the rock volume Vaisblat et al., 2016). ...
... Davies et al., 1997;Orchard and Zonneveld, 2009;Crombez et al., 2016;Davies et al., 2008;Proverbs et al., 2018;Zonneveld and Moslow., 2018). The Montney unconformably overlies the Permian Belloy Formation and is truncated from above by the Coplin and sub-Jurassic unconformities (Gibson and Edwards, 1990;Edwards et al., 1994;Davies et al., 1997;Moslow 2000) (Figure 2). ...
... The mineralogical assembly in the Monteney Formation consists of quartz, feldspars, micas, calcite, dolomite, iron-dolomite, low expandability mixed-layer illite smectite clays (MLIS), and pyrite, with minor amounts of apatite, barite, kaolinite, chlorite, and heavy minerals Barber, 2003;Derder, 2012;Playter, 2013;Crombez, 2016;Vaisblat et al.,2016). Grain size in the Montney Formation varies from very fine sand to clay-size material, with a slight increase in grain size (to fine sand) toward the eastern margins of the formation (Gibson and Edwards, 1990;Edwards et al., 1994;Davies et al., 1997;Zonneveld et al., 2011;Vaisblat et al., 2016). The main control over rock composition is diagenetic, with early extensive cements accounting on average for a third of the rock volume Vaisblat et al., 2016). ...
... Data presented in this report permit additional comment on the lithostratigraphic identity of this succession in Mount Martin and Mount Merrill map areas. Although the exposed succession contains abundant shale and siltstone, it lacks the shale-dominant character of typical Grayling Formation (Kindle, 1944;Gibson and Edwards, 1990). However, its relatively high shale and siltstone content disallows lithostratigraphic correlation with the sand-rich Liard Formation or with younger, carbonate-dominated Triassic formations (Gibson and Edwards, 1990;Zonneveld and Gingras, 2001). ...
... Although the exposed succession contains abundant shale and siltstone, it lacks the shale-dominant character of typical Grayling Formation (Kindle, 1944;Gibson and Edwards, 1990). However, its relatively high shale and siltstone content disallows lithostratigraphic correlation with the sand-rich Liard Formation or with younger, carbonate-dominated Triassic formations (Gibson and Edwards, 1990;Zonneveld and Gingras, 2001). ...
In the Mount Martin and Mount Merrill map areas, Yukon Territory, 300 to 400 m of interbedded shale, siltstone, and sandstone are preserved between the top of the Permian Fantasque Formation and the base of Cretaceous strata (Chinkeh and Garbutt formations). Based upon two detailed strati-graphic sections, preliminary sedimentological and stratigraphic study of this succession has been undertaken. Five facies associations are recognized, and are interpreted to record deposition on a wave-dominated siliciclastic shelf in environments ranging from distal shelf to upper shoreface. Upward -coarsening packages (10–40 m thick) are common. The succession can be roughly subdivided into four units. In ascending order these are a basal, recessive (shale-dominated?) unit, a sandstone-rich unit, a shale-rich unit, and an upper unit containing sandstone and shale in subequal proportions. Regional comparison of stratigraphic position, lithology, and trace-fossil assemblages suggests a tentative correlation with the Lower to Middle Triassic Toad Formation.
... The age of the Triassic Montney Formation ranges from the Griesbachian to the Spathian [16]. According to [15], in most locations, carbonate layers of Carboniferous to Permian age sit unconformably upon the Triassic succession [15,[17][18][19]. ...
Hydrocarbons in self-sourced reservoirs are determined by the concentration and maturation of organic matter in sediments. As a result, lowering risk in unconventional resource research and development requires knowledge of hydrocarbon potentiality factors. The geochemical data for the Montney Formation samples studied suggest that it is a fair to good source rock with type IV kerogen that can generate gas in general. The statistical modelling of the analyzed data reveals a valuable technique for identifying characteristics, clusters, and linkages that affect source rock assessment. The Spearman’s correlation coefficient showed a good positive correlation between the total organic carbon (TOC) and free hydrocarbons (S1), generating potential (S2), and potential yield (GP). There was a weak correlation with the maturity index (Tmax) and hydrogen index (HI) and a highly negative correlation between the TOC and oxygen index (OI). On the other hand, the principal component analysis (PCA) showed the presence of three factors affecting the source rock evaluation. Factor 1 included TOC, S1, and S2, which are related to organic richness and hydrocarbon potentiality; factor 2 contained the production index (PI), and the generated CO2 (S3) was related to the organic matter source. Factor 3 included the Tmax and HI related to the type of organic matter and thermal maturity. In addition, the TwoStep cluster analysis separated the source rock in the study area into two major groups. Cluster 1 is characterized relatively by high HI, TOC, S1, S2, and PI, with Tmax < 455 °C indicating good source rock in the mature level with the capability to generate little oil and condensate gas. Cluster 2 is characterized by relatively low HI, TOC, S1, S2, and PI, with Tmax > 455 °C, indicating an over-mature source rock in the dry gas window.
... The formation is bounded from below by the Permian-Triassic unconformity and from above by the Coplin and sub-Jurassic unconformities to the east (Fig. 2) (Gibson and Edwards, 1990;Edwards et al., 1994;Davies et al., 1997;Moslow, 2000). In the western parts of the basin where the Coplin and sub-Jurassic unconformities cut through younger formations, the Montney is overlain by the Doig Formation or the Sunset Prairie Formation (Fig. 2) (Furlong et al., 2018). ...
The detrital grain size of siltstone reservoirs occupies a middle ground between sandstones and shales, both of which are better understood in terms of their petrophysical properties. Because siltstones can be important hydrocarbon reservoirs, we examine controls on petrophysical properties in the Lower Triassic Montney Formation in western Canada, which hosts world-class reserves of gas, gas liquids and oil. We focus on the effects of rock fabric (including grain size) and composition on pore system characteristics and permeability, drawing contrasts between the three reservoir types.
The Montney Formation is an unconventional reservoir through most of its subcrop, with porosities ranging from ∼3 to 7.5% and permeabilities in the micro to nano Darcy range (6.5*10⁻⁶ mD to 5.6*10⁻² mD). Shale reservoirs worldwide are characterized by similar porosity and permeability values, with porosity of up to 8% (rarely up to 15%) and permeability in the nano to micro-Darcy range.
Quartz, clay, and organic matter abundance influence the petrophysical properties of the Montney siltstone. Quartz content exerts a positive control on both porosity and permeability by strengthening the rock framework and reducing porosity loss due to compaction. Elevated clay content is also associated with higher porosity and permeability, in part because of a depositional association with quartz, and in part because clays locally shelter interconnected primary porosity that promotes permeability. Organic matter content is negatively correlated to porosity and permeability despite the presence of organic matter porosity because relict oil (now solid bitumen) occludes primary pores and because other pore types contribute a greater fraction of the total pore volume. Lithofacies, characterized in four cores, are indistinguishable on the basis of petrophysical properties, due to their similar grain size and composition and the massive overprinting by shallow burial diagenesis.
While the pore system evolution of sandstones is mainly controlled by the mechanical compaction of hard grains and cementation, pore system evolution of shales is primarily controlled by compaction of ductile grains and diagenesis of primary organic matter, in addition to cementation. Porosity and permeability values of the Montney siltstones are similar to those of shale formations, but the controls on pore system evolution of this intermediate grain size reservoir are predominantly controlled by processes similar to sandstones: compaction, cementation, and cement dissolution. Minor contribution from secondary porosity in bitumen affects some sections of the reservoir in a way that is similar, but not identical, to shale reservoirs.
... The lower Triassic MF was assigned to the Griesbachian to Spathian in age [19] (Fig. 2). In nearly most places, the Triassic sequence overlies unconformably overlies the Carboniferous to Permian (Belloy Formation) strata [15,[21][22][23]. The Triassic sequence's cumulative thickness is approximately 1200 m in the J o u r n a l P r e -p r o o f westernmost outcrop in the Rocky Mountain bottoms [21]. ...
Montney Formation (MF) source rock located in northeastern British Columbia (BC), Canada, was analyzed to determine its depositional conditions and organic matter source input other than to determine their level of thermal maturity. The high total sulfur (TS) (2.23-20.86 wt.%) and good to very good total organic carbon (TOC) content (0.3-5.87 wt.%) in the analyzed samples give good evidence that the deposition of MF source rock was in a marine environment under reducing conditions. A mixed marine-terrestrial derived organic matter (OM) for the Montney source rock that was deposited in a marine dysoxic environment is deduced from the composition and distribution of different biomarker traces. Thus, the previous result is supported by the high short-chain n-alkanes ratio, accompanied by carbon preference index (CPI) around unity, high concentration of tricyclic terpanes, high C24 tricyclic/C24 tetracyclic, hopane/sterane ratios ranging from low to moderate, as well as the relationship between regular sterane compositions. During deposition of the MF source rock, it can be noticed that more land organic materials this was deduced according to the high waxiness index. From maturity ratios of Ts/(Ts+Tm), C32 22S/(22S + 22R) homohopane, moretane/hopane and 20S/(20S+20R) and ββ/(ββ + αα) C29 it can give a conclusion that the source rock is mature to postmature of hydrocarbon generation.
... The isopach map of the Montney Formation shows its depositional slope toward the northeast along the paleolow ( Figure 1). It is thickest in the center of the Peace River Embayment but gradually thins eastwards, where the outcrop limit is truncated by the Jurassic strata [26,28,33]. The paleostructure influenced the depositional trends and facies distribution/development of three distinctive stratigraphic units [28,34]. ...
The presence of lamination on sedimentary rocks is a distinct characteristic, particularly in shales. They are distinct due to the contrast between successive layers with regard to grain size, composition, color, and sedimentary structures, such as graded beds. Typically, the degree of lamination is controlled by the sedimentation rate and flow regime. Herein, we developed a mudstone classification scheme in terms of lamination because lamination-based shale facies are related to differing features in mineral composition, porosity, and Young’s modulus. This study also attempts to verify whether wireline log patterns are relevant to shale lithofacies. The relationship between the porosity and lamination of the Montney Formation can be used to estimate reservoir properties. Our results show that an increased silt lamina in mudstone leads to an increase in the quartz and calcite contents and a decrease in the clay content, which increases the porosity, permeability, and Young’s modulus. However, reservoir quality is not solely dependent on lamination because of the complex interaction between components. The degree of lamination affected the neutron, density, and sonic log responses. Furthermore, the presence of lamination tends to decrease the neutron percentage, with similar trends in density and sonic log box plots in the study area. When the percentage of clay or cement material decreases, the neutron and density log responses diminish. Meanwhile, when the rock texture variation increases with an increase in the degree of lamination, the sonic log response decreases.
... The Montney Formation is bounded below by the Permian-Triassic unconformity and above by the Coplin and the sub-Jurassic unconformities (Gibson and Edwards, 1990;Edwards et al., 1994;Davies et al., 1997;Moslow 2000). The Montney Formation thickens and deepens from the northeast to the southwest to a thickness of over 350 m and burial depth greater than 2500 m. ...
We develop a two-phase (gas/water) flow model to simulate water imbibition into the face of a hydraulic fracture. The model incorporates water suction potential values measured with a dew-point psychrometer, which has distinct advantages over standard mercury injection tests, to measure water suction potential in tight rocks. The model accurately predicts water imbibition into core plugs from the Montney Formation under lab conditions. We then apply the model to simulate water leak-off per unit fracture area during a typical frack stage and the subsequent soaking period. Our results show that a 0.3 meter invaded zone develops from the fracture face into the formation at the end of 30 days of soaking. High water saturation in the invaded zone dissipates into the rock after two months of production, due to high capillary pressures (suction potential).
We selected 120 wells in close proximity in the northern Montney play to build a case study. Pertinent load recovery data such as water injected, water recovered, and soak-time were collected for each well. Using the simulation results and field data, we estimated the fracture surface area created or stimulated during hydraulic fracturing for each well. The wells’ production performance shows a clear relationship with the calculated fracture surface area of the wells, which averaged 250,000 m² per stage.
This methodology can be used to assess the future well performance immediately after flowback. Applying this method to a region can assist operators in identifying sweet spots in their assets in terms of presence of brittle rocks or natural fracture networks. In addition, the estimate of fracture surface area can constrain discrete fracture models.
... Prior to the Triassic, the Peace River Arch was a basement-uplifted topographic high, which persisted from the Precambrian to Devonian and greatly controlled deposition and preservation of sediment (de Mille, 1958;Cant, 1988;Stephenson et al., 1989;Barclay et al., 1990;O'Connell et al., 1990). During the Carboniferous, the Peace River Arch began to subside and collapse, which eventually formed the Dawson Creek Graben Complex (Barclay et al., 1990;Gibson and Edwards, 1990;O'Connell et al., 1990). The graben complex consists of three major elements, which comprise the Fort St. John Graben, the Hudson Hope Low and a number of smaller satellite grabens (Hines Creek, Whitelaw and Cindy grabens; Barclay et al., 1990;O'Connell, 1994). ...
The Middle Triassic Sunset Prairie Formation has been recently identified between the Lower Triassic Montney Formation and the Middle Triassic Doig Formation in the Western Canada Sedimentary Basin. Due to its recent recognition, the Sunset Prairie Formation has yet to be incorporated into sequence stratigraphic frameworks of the Triassic. Through the investigation of 25 cored wells, facies characteristics, vertical facies stacking and lateral facies distributions have been identified and described. Sequence stratigraphic surfaces were identified in core and extrapolated to geophysical wireline log signatures of 248 wells within the basin. The Sunset Prairie Formation can be divided into three, upward‐coarsening parasequences that exhibit a retrogradational stacking pattern. All parasequences of the Sunset Prairie Formation are truncated at their tops by the Doig phosphate zone. The Sunset Prairie Formation truncates the underlying Montney Formation, suggesting that the stratigraphic interval is unconformity bound by sequence boundaries and their correlative conformities. The addition of the Sunset Prairie Formation reveals a discrete sequence of transgressive deposits previously unaccounted for within the Triassic sequence stratigraphic framework of the Western Canada Sedimentary Basin.
... In addition to the, Rocky Mountain Fold and Thrust Belt, which formed in response to compression during the Late Cretaceous, major structural features influencing the region include the Late Carboniferous Dawson Creek Graben Complex (Davies, 1997a;O'Connell et al., 1990;Barclay et al., 1990;Gibson and Edwards, 1990) (Fig. 1a). Recurrent movement along the structures associated with the Dawson Creek Graben Complex influenced deposition throughout the Mesozoic, including the early Triassic Montney succession (Moslow, 2000). ...
In the Regional Heritage Field of northeastern British Columbia, Canada, the Lower Triassic Montney Formation consists of up to 320 m of bituminous, dolomite-cemented, arkosic, siltstone that forms a continuous, basin-centred, hydrocarbon accumulation. An integrated sedimentological and ichnological analysis of cores taken from across the field, suggests that the Montney Formation features three main facies: shelf, distal prodelta and proximal prodelta. The shelf facies records deposition below storm wave base in a suboxic environment. The distal prodelta facies reflects deposition above storm wave base, in a setting that was subject to continuous paleoenvironmental fluctuations. The proximal prodelta facies was deposited between fair-weather and storm wave-base, in a setting that was periodically influenced by storms. The stratigraphic architecture of the Montney Formation consists of a series of offlapping clinoforms that comprise at least three unconformity-bounded, depositional sequences, informally named Sequence 1, 2, 3, in ascending order. These sequences are interpreted to reflect the construction of a relatively shallow marine shelf that was fed, primarily, by ephemeral rivers in an arid to semi-arid setting. A reconstruction of the depositional history of Sequence 3 places the reservoirs of this extensively targeted interval into facies and sequence stratigraphic context. The reservoir and production characteristics associated with the lowstand systems tract of Sequence 3 is examined, in order to identify and establish relationships between reservoir quality distribution and horizontal gas-well productivity in the Regional Heritage Field. The analysis reveals that the observed regional variability in horizontal well productivity is controlled, primarily, by the thickness and quality of the reservoir, as well as by factors that influence the relative permeability to gas. These factors include the distribution of hydrocarbons within the reservoir, and the associated water saturation. This study demonstrates that a detailed and comprehensive understanding of the depositional processes and sequence stratigraphy associated with the Montney Formation is fundamental to the exercise of defining sweet spots in this otherwise continuous reservoir. © 2018, Canadian Society of Petroleum Geologists. All rights reserved.
... The Montney Formation is separated from the overlying Doig Formation by a strongly radioactive, high gamma ray (GR) reading on well logs (Figure 2), and phosphate rich interval known informally as the "Doig Phosphate Zone" [3] [18]. This boundary is an erosional surface, and has the same paleomagnetic record of normal polarity, which likely corresponds to the normal polarity interval MT2 in the bottom of the Anisian age that starts at ~245 Ma [19]. ...
Several decades of conventional oil and gas production in Western Canada Sedimentary Basin (WCSB) have resulted in maturity of the basin, and attention is shifting to alternative hydrocarbon reservoir system, such as tight gas reservoir of the Montney Formation, which consists of siltstone with subordinate interlaminated very fine-grained sandstone. The Montney Formation resource play is one of Canada’s prime unconventional hydrocarbon reservoir, with reserve estimate in British Columbia (Natural Gas reserve = 271 TCF), Liquefied Natural Gas (LNG = 12,647 million barrels), and oil reserve (29 million barrels). Based on sedimentological and ichnological criteria, five lithofacies associations were identified in the study interval: Lithofacies F-1 (organic rich, wavy to parallel laminated, black colored siltstone); Lithofacies F-2 (very fine-grained sandstone interbedded with siltstone); Lithofacies F-3A (bioturbated silty-sandstone attributed to the Skolithos ichnofacies); Lithofacies F-3B (bioturbated siltstone attributed to Cruziana ichnofacies); Lithofacies F-4 (dolomitic, very fine-grained sandstone); and Lithofacies F-5 (massive siltstone). The depositional environments interpreted for the Montney Formation in the study area are lower shoreface through proximal offshore to distal offshore settings. Rock-Eval data (hydrogen Index and Oxygen Index) shows that Montney sediments contains mostly gas prone Type III/IV with subordinate Type II kerogen, TOC ranges from 0.39 - 3.54 wt% with a rare spike of 10.9 wt% TOC along the Montney/Doig boundary. Vitrinite reflectance data and Tmax show that thermal maturity of the Montney Formation is in the realm of “peak gas” generation window. Despite the economic significance of the Montney unconventional “resource-play”, however, the location and predictability of the best reservoir interval remain conjectural in part because the lithologic variability of the optimum reservoir lithologies has not been adequately characterized. This study presents lithofacies and ichnofacies analyses of the Montney Formation coupled with Rock-Eval geochemistry to interpret the sedimentology, ichnology, and reservoir potential of the Montney Formation tight gas reservoir in Fort St. John study area (T86N, R23W and T74N, R13W), northeastern British Columbia, western Canada.
... The main subsidence in the basin continued to be centred on the axis of the DCGC, where the thickest Triassic section is deposited. Subtle, local movement along underlying Carboniferous horst and graben blocks caused variations in the Triassic isopach and facies trends (Gibson and Barclay, 1989;Gibson and Edwards, 1990). Westward thickening of Triassic strata beneath the Coplin Unconformity has been shown to be primarily the result of tilting and erosion, not differential sedimentation on the western side of extensional faults . ...
Recent discoveries of kimberlites and polymetallic mineralization in the sedimentary succession of the Alberta Basin have increased interest in the mineral potential of Alberta. In order to promote exploration for and mining of non-energy minerals in Alberta, the Alberta Government is putting increased effort into providing basic geological information in support of the minerals industry.
Mineral exploration is critically related to knowledge of the location and age if fractures, which may have acted as pathways for mineralizing fluids and kimberlite emplacement. Therefore, a regional compilation of the known and interpreted subsurface and surface structural features and current knowledge of the tectonostratigraphic evolution in northern Alberta was conducted as a first step to aid government and industry in their efforts to better target possible occurrences of non-energy minerals in the province.
An innovative approach in both handling and delivering geological information has been taken in this compilation. Lineaments from various literature sources (digital and nondigital) were geospatially referenced, compiled digitally into ArcView(r) layers(I.e., shapefiles) and individually tagged with attribute data stored in a database.
This report provides an overview of the Late Proterozoic to Recent tectonostratigraphic evolution of northern Alberta, in order to facilitate understanding of the geological significance of the compiled structural features (accessible through ArcExplorer(r) on the enclosed CD-ROM).
The Phanerozoic geological evolution of northern Alberta is dominated by an east-northeast-trending geological subsurface structure, traditionally called the Peace River Arch (PRA). Several distinct phases of Phanerozoic tectonic evolution have been documented: 1) an Early to Middle Paleozoic arch phase, 2) a Carboniferous to Triassic embayment phase, and 3) a Jurassic to Cretaceous deep basin or downwarping phase.
Aspects that may be relevant for both energy and non-energy minerals are addressed, with particular emphasis exploration for sediment-hosted mineral deposits within each tectonostratigraphic phase. Recommendations for further integrated studies, investigating the basement sedimentary cover interactions, are made.
... The Pardonet Formation in British Columbia is a deep-water, carbonaceous-argillaceous limestone representing the final phase of a Late Triassic marine transgression. Deposition is believed to have occurred in a relatively deep water distal shelf setting (Gibson and Barclay 1989;Gibson and Edwards 1990). At all localities, Sikannisuchus is associated with the remains of shastasaurid ichthyosaurs, which are fully adapted to the marine environment. ...
Sikannisuchus huskyi, a new genus and species of archosaur, is described from the Upper Triassic (Norian) Pardonet Formation of northeastern British Columbia. It has a broad, flat skull, and may have reached 4 m in length. It is referred to the Archosauria on the basis of a lateral mandibular fenestra, laterally compressed serrated teeth, elongate transverse processes, neural spine table, osteoderms, and thecodont dentition. It is autapomorphic in that the postfrontal enters the border of both the orbit and the supratemporal fenestra, and it has a large prefrontal that contacts both the nasal and the postfrontal, excluding the frontal from the margin of the orbit. The presence of osteoderms and a well-developed clavicle exclude Sikannisuchus from the Ornithodira; however, in the absence of any preserved limb material, we cannot assign it to the Crurotarsi. Sikannisuchus is not currently referable to any known taxon of archosaur and is left as Archosauria incertae sedis.
... The Pardonet Formation was first introduced by McLearn (1940) as a member of the Schooler Creek Formation and subsequently elevated to formational status (McLearn, 1960) with the type locality on Pardonet Hill along the Peace River. Subsequently, regional understanding of the Pardonet Formation was greatly improved by the investigations by Gibson (1974Gibson ( , 1975, and more recently by Gibson and Edwards (1990), Edwards et al. (1994), Davies (1997b), Zonneveld and Gringas (2001), and Zonneveld et al. (2004, in press). As presently understood, the Pardonet Formation consists of a westward thickening series of dark grey carbonaceous silty limestones with minor amounts of dark mudshale and dolomitic siltstone. ...
The Upper Triassic of the Williston Lake area of northeastern British Columbia is represented by a nearly continuous series of fossil-rich sediments that were deposited in the Western Canadian Sedimentary Basin in an offshore mid-paleolatitude setting on the western margin of cratonic Pangea. The fossils in this report come primarily from the upper Carnian—upper Norian Pardonet Formation, which has been the subject of numerous paleontologic studies on ammonoids and conodonts, yet has received little attention with regard to its bivalve fauna. Fossil bivalves belonging to the thin-shelled bivalve genera Halobia, Eomonotis, and Monotis dominate the benthic macrofauna and occur within unique shell accumulations that are interpreted to represent oxygen-controlled monospecific paleocommumities that have undergone little post-mortem transportation. Systematic analyses of more than 1,000 individual bivalve specimens resulted in the identification of 25 species-rank taxa, a majority of which belong to the pterioid genus Halobia and the pectinoid genera Eomonotis and Monotis. Of these, four new species are recognized, including 1) upper Carnian Halobia tozeri n. sp. characterized by a unique triangular outline; 2) lowermost Norian Halobia selwyni n. sp. closely related to H. beyrichi and first appearing with H. austriaca which is proposed as a potential datum for the Carnian—Norian boundary; 3) Norian Meleagrinella mclearni n. sp., a new name for previously identified species; and 4) upper Norian Otaparia norica n. sp. which has a delicate thin shell, unique outline, and fine ornament. A revised and refined biochronology of Upper Triassic Bivalvia (chiefly Halobiidae and Monotidae) integrated with conodont and ammonoid zones and standard Triassic stages is presented for the Upper Triassic of the Williston Lake area and permits enhanced correlation to coeval faunas elsewhere in the North American Cordillera, and to the Boreal, Panthalassan and Tethyan faunal realms.
Diagenetic models for silt-rich mudstone (siltstone) are less advanced than those for sandstone and clay-rich mudstone. In addition, the influences of diagenetic processes on reservoir quality in siltstone formations are poorly understood. Here we examine the roles of depositional facies, detrital composition, and diagenetic processes in the compositional evolution and reservoir quality of the Lower Triassic Montney Formation, a prominent siltstone-dominated reservoir in western Canada with very large reserves of oil, gas-liquids and natural gas. We applied high-resolution, advanced petrographic methods including FEG-SEM (SE, BSE, EDX and SEM-CL), XRD, and QEMSCAN technologies, as well as He-pycnometry on samples from 17 different locations that represent a range of depths and thermal maturities. Cross-cutting and overgrowth relationships and volumes of authigenic phases demonstrate massive precipitation of quartz, feldspar, dolomite, calcite and anhydrite cements at shallow burial depths, leading to compositional homogeneity among different lithofacies. Unlike clay-rich mudstone, siltstones preserve relatively high porosity and permeability at shallow burial depth, which allow for relatively high rates of fluid flow through the rock, possibly driven by reflux of concentrated seawater in nearshore saltpans. In contrast to sandstones, deep burial diagenesis played a relatively minor role in the compositional evolution of the Montney Formation siltstone and which is expressed in the form of pressure solution and minor amounts of fibrous illite precipitation.
Between the Lower Triassic Montney Formation and the Middle Triassic Doig Formation, there is an unconformity-bound interval recently identified as the Sunset Prairie Formation which occurs on a regional scale within eastern British Columbia. The interval is Middle Triassic in age and is characterized by interbedded light grey, pervasively bioturbated sandstone and dark grey, minimally bioturbated siltstone. Trace fossils present within the interval include Phycosiphon, Rosselia, Cylindrichnus, Teichichnus, Asterosoma, Scolicia, Helminthopsis, Palaeophycus, Chondrites, Planolites, Diplocraterion, Rhizocorallium, Thalassinoides, Skolithos and Zoophycos, which are indicative of the Cruziana Ichnofacies. Seven facies are identified, based on sedimentological, ichnological and paleontological analysis of core. They are interpreted to have been deposited in offshore, offshore transition and lower shoreface environments, which were weakly storm affected. The unconformity bound unit exhibits flooding surface sequence boundaries at its top and base, and internal geometries of the facies stacking suggest retrogradational parasequence sets. The Sunset Prairie Formation overall thickens to the west, but is spatially complex due to the deposition and preservation of the interval being influenced by structural features within the basin. The Sunset Prairie Formation is thickest (80 m) within the Fort St John Graben system and Hudson Hope Low. The Sunset Prairie Formation provides the first regionally expansive, highly bioturbated assemblage of diverse trace fossils within the Middle Triassic strata of the Western Canada Sedimentary Basin. Bioturbation is limited to the proximal offshore to lower shoreface settings, which is similar to the few examples of diverse ichnological assemblages within the Montney Formation. However, those earlier published examples are associated with refugia environments and are not laterally extensive. The lateral distribution of the Sunset Prairie Formation suggests that favorable environmental conditions were widespread during the earliest Middle Triassic (Anisian) and could play a key role in understanding the biotic recovery following the end-Permian mass extinction. © 2018, Canadian Society of Petroleum Geologists. All rights reserved.
This study presents the first published subsidence analysis during the deposition of the Montney Formation. It was deposited during the Early Triassic (ca. 252.2–245 Ma) in the Western Canadian Sedimentary Basin (WCSB) located along the western margin of the North American craton. Subsidence analyses of six representative wells and two outcrop sections along a proximal to distal transect are presented using a backstripping method integrating recent high-resolution stratigraphic correlations for the Montney Formation. The entire Paleozoic to Cenozoic sedimentary column of the WCSB was backstripped to put the deposition of the Montney Formation into a broader context and provide results regarding the type of subsidence and geodynamic setting for the Montney Formation.
The spatial and temporal evolution of the subsidence during the deposition of the Montney Formation indicates that the most likely basin setting is a foreland. The tectonic subsidence during the Triassic is herein interpreted as a combination of the topographic loading of the orogenic wedge (flexure) and the sublithospheric ‘‘loading’’ caused by slab load-driven subsidence (dynamic subsidence). This suggests that the retro-foreland basin setting was associated with an eastward dipping subduction during the deposition of the Montney Fm.
Three foreland stages are thus recorded in the whole WCSB, with evidence for: 1) a Late Permian (fore-arc) pro-foreland setting; then 2) a Triassic collisional retro-foreland basin prior to the well-known; 3) Jurassic-Cenozoic collisional retro-foreland.
Between the Lower Triassic Montney Formation and the Middle Triassic Doig Formation, there is an unconformity-bound interval recently identified as the Sunset Prairie Formation which occurs on a regional scale within eastern British Columbia. The interval is Middle Triassic in age and is characterized by interbedded light grey, pervasively bioturbated sandstone and dark grey, minimally bioturbated siltstone. Trace fossils present within the interval include Phycosiphon,
Revised lithostratigraphic correlations reveal that the current stratigraphic nomenclature for the Middle Triassic within the subsurface of the Western Canada Sedimentary Basin needs modification. This paper introduces a new formation, the Sunset Prairie Formation, for an interval of interbedded light grey, pervasively bioturbated sandstone and dark grey, minimally bioturbated to non-bioturbated siltstone, which sits stratigraphically between the Lower Triassic Montney Formation and the Middle Triassic Doig Formation within northeastern British Columbia, Canada. The Sunset Prairie is sedimentologically, ichnologically and paleontologically distinct from the overlying and underlying formations and warrants a new formational name to be established. The Sunset Prairie consists of seven lithofacies which are interpreted to have been deposited within offshore, offshore transition and lower shoreface settings. There is limited preservation of physical sedimentary structures due to pervasive bioturbation but, where preserved, include planar-, pinstriped-, planar-wavy and wavy laminae, low and high angle planar cross laminae, asymmetric ripples, hummocky cross stratification and penecontemporaneous deformation structures. Trace fossils present within the interval include Phycosiphon, Rosselia,
The Peace River Arch in northwestern Alberta and northeastern British Columbia is a cratonic uplift that was formed at a high angle to the passive margin during the Late Proterozoic. The Arch was an asymmetrical structure, with major uplift along an east-west-trending fault zone at its northern edge. The Arch structure overprinted the pre-existing Precambrian basement structure. Durings its history, the Peace River Arch has existed in three different forms: a Late Proterozoic to early Paleozoic Arch, a late Paleozoic to earliest Mesozoic Embayment, and as a deep basin component of a Mesozoic foreland basin. No firm conclusions can presently be drawn regarding the origin of the Peace River Arch, but several possibilities are suggested. The original Arch structure, at the Upper Proterozoic continental margin, was possibly formed by uplift related to the cratonward extension of an oceanic fracture zone. The extensional history of the Early Carboniferous graben complex suggest a possible origin in a failed rift setting. The arch-embayment related subsidence during the Cretaceous likely was caused by regional loading of the structure at the western margin. -from Authors
The dominant view of Middle Triassic stratigraphy in western Alberta and northeastern British Columbia includes westward regression, via offlapping parasequences, continuously from the Doig Formation upward through the Halfway and the lower part of the Charlie Lake Formation to the Coplin Unconformity. The Doig-Halfway contact is arbitrarily picked within a succession of stacked parasequences. Some writers portray the Charlie Lake Formation as mildly unconformable above the Halfway; others depict the contact as conformable and time-transgressive, as the Charlie Lake is interpreted as a mainly nonmarine sabhka facies overlying regressive Halfway beach sands. In the Umbach-Wargen area of British Columbia, few of these entrenched models seem to apply; instead, the Halfway appears to overlie unconformably a truncated Doig Formation, forming a succession of stacked retrogradational and/or transgressive parasequences, which onlap progressively towards the northeast a structural high on the Doig. In addition, the Charlie Lake Formation forms a succession of widespread, correlateable parasequences, more akin to those deposited in shallow marine conditions rather than nonmarine. These strata overlie the beach sands of the Halfway Formation as its coeval, marine offshore equivalent. If the Charlie Lake Formation is an offshore, basinward equivalent to some of the Halfway shoreline sands, then depositional models have to be re-examined.
The Lower Triassic Montney Formation in west-central Alberta is divided into two major third-order sequences separated by a sequence boundary that correlates to an Early Triassic (Smithian/Dienerian) global eustatic sea level fall. This drop in sea level enhanced mass-wasting processes responsible for the formation of a turbidite channel and lobe complex within the lowstand systems tract of the upper Montney sequence. This assemblage of facies constitutes the principal reservoir within the Valhalla-La Glace fields. Most of the turbidite reservoirs facies were derived from the reworking of a southwestward-prograding depositional thick, designated the "Cindy Lobe", of the lower Montney sequence that protrudes basinward from the western extension of the Cindy Graben trend. The Valhalla-La Glace reservoir facies are a complex of turbidite channels and downdip lobes deposited in the subaqueous platform of a prograding lowstand shoreline immediately seaward of a continental ramp slope break. The ramp "edge" trends NNW-SSE through the area, and defines the updip depositional limit of turbidite facies. The rampedge orientation is probably fault controlled and marks the onset of rapid and abrupt thickening of lowstand facies associations. The origin of these facies is attributed to mass-wasting and generation of sediment gravity flows due to substrate instability at the slope break. Individual turbidite channels likely have undergone headward retreat, moving upslope and creating their own supply of sediment for turbidity flows. Lateral facies relationships expressed by turbidite channel, channel margin and levee/overbank facies provide a predictive model for determining proximity to the turbidite channel axis. The turbidite channel facies association contains the highest quality reservoir in terms of porosity and permeability. Turbidite channels can be amalgamated or crosscut one another, thus inducing vertical and lateral permeability barriers and reservoir heterogeneity. However, there is a lateral continuity in lithofacies along depositional strike and dip. The reservoir facies are more continuous along depositional dip. Turbidite channel, turbidite channel margin, and turbidite lobe facies associations are recognized within the study area. The latter is found almost exclusively within the Glacier field. Facies associations and their lateral variability within the study area are analogous to turbidite channels and lobes from the subaqueous platform of the Fraser River delta, providing a process sedimentologic and geomorphic analogue for the Valhalla-La Glace field reservoir facies.
The carbonate-dominant Upper Triassic Baldonnel and Pardonet formations were deposited in the west-facing extensional Peace River Basin, in a midlatitudinal setting on the northwestern margin of the supercontinent Pangea. Subsurface distribution of the Pardonet is restricted to northeastern British Columbia, but the Baldonnel extends into west-central Alberta. This paper describes the stratigraphic framework, internal subdivisions, composition, facies and depositional setting of the two units and discusses the relationship between the overlying uppermost Triassic Bocock Formation and the Pardonet. A number of unconformities and flooding surfaces in the underlying upper Charlie Lake Formation, and in the Baldonnel and Pardonet, are documented, including two newly defined unconformities. Facies maps for the Baldonnel and Pardonet north and south of the Peace River-Williston Lake area in northeastern British Columbia demonstrate the westward-deepening ramp setting of these units and the influence of paleostructure on facies. Facies changes and increase in thickness of both the Baldonnel and the Pardonet in the Foothills of northeastern British Columbia south of Williston Lake reflect the influence of the southwestern extension of the Fort St. John Graben. The structural low defined by this extension is designated the Hudson Hope Embayment in this paper. The Embayment lies north of the northern termination of the upper Paleozoic Sukunka Uplift, which is roughly parallel to and en echelon with the Permian Beatton High to the northeast. Although the influence of these two highs on Triassic sedimentation, if any, remains unclear, the Baldonnel is thinned and the Pardonet missing over a smaller structural high on trend with the western end of the Beatton High. The boundary between the underlying Upper Triassic Charlie Lake Formation and the Baldonnel Formation in northeastern British Columbia is diachronous. The trace of the Siphon unconformity demonstrates this diachroneity most clearly: in the type section well of the Charlie Lake and Baldonnel formations near Fort St. John in British Columbia, the Siphon unconformity lies about 50 m below the "type" boundary between the two units but farther westward, in the Foothills of British Columbia (Cypress-Sikanni area), the formation boundary lies at or a few metres above the Siphon unconformity. Sequence-stratigraphic interpretations of the uppermost Charlie Lake-Baldonnel transition suggest that it represents a retrogradational transgressive systems tract that extends through northeastern British Columbia into west-central Alberta, where it includes the Worsley Member of the upper Charlie Lake Formation. The Baldonnel and Pardonet formations are the youngest major carbonate reservoir facies (outside the Williston Basin) in western Canada. Initial in-place reserves for crude oil for the combined units are 6 ×106m3 (38 million barrels), and 132 × 109m3 (4.7 Tcf) of raw gas, with the latter exceeding 9 Tcf if projected reserves in the Monkman trend in the Foothills of northeastern British Columbia are included.
The diagenetic controls on reservoir quality of Middle Triassic reservoir facies are addressed in this paper because their importance is paramount to the understanding of reservoir performance. In this study, reservoir quality is compared and contrasted for two reservoir lithofacies and the implications of porosity structure on efficiency of primary and secondary hydrocarbon recovery is assessed. Middle Triassic reservoir facies of the Peejay Field are confined to the youngest of four parasequences. This parasequence is a prograding shoreface succession containing tidal-inlet deposits. Tidal-inlet fills form the main reservoir facies and are composed of sublitharenites (lithofacies H) and bioclastic grainstones (lithofacies G). Tidal-inlet sand bodies are 4-6 km long, 500 metres wide, up to 11 metres thick, and are oriented parallel to the paleoshoreline. Vertical profiles of reservoir quality (permeability and porosity) decrease upward, with variance of values being less for the sublitharenites than for bioclastic grainstones. Sedimentary structures, sediment texture, pore type, size and degree of connectivity control reservoir quality and production. The main porosity type of the sublitharenites is secondary intergranular and characterized by homogeneously connected pores, wide pore-throats and low aspect ratios. In comparison, effective biomoldic porosity of bioclastic grainstones is dependent on the degree of intercrystalline porosity development in matrix dolomites. The high porosity and low permeability values of the bioclastic grainstones may lead to the inefficient flushing of hydrocarbons during waterflooding.
Abundant hydrocarbons have been produced from the Middle Triassic Halfway Formation of northeastern British Columbia; however, the facies relationships and geological history of this strata are poorly understood. To address these issues, 132 cores an well logs from 345 wells were examined from the Peejay Field of northeastern British Columbia in order to: 1) establish a depositional model; 2) identify the origin of all reservoir facies; and 3) construct an exploration model to better predict the trend of reservoir facies. Middle Triassic deposits of the Peejay Field comprise four west-southwestward prograding shoreface parasequences which form a progradational parasequence set. Palaeoshoreface deposits, referred to as Lithofacies Succession I (L.S.I), have been truncated and replaced with sharp-based cross-stratified bioclastic grainstone and litharenite tidal inlet fills, referred to as Lithofacies Succession II (L.S.II). Tidal inlet fills trend north-northwest to south-southeast and exhibit the best reservoir quality in the field. Successively younger parasequences are thicker and contain coarser grained lithofacies. However, the youngest parasequence (P.A. 4) varies laterally in thickness due to postdepositional erosion. Isopach maps and cross-sections through the Middle Triassic strata reveal the occurrence of a post-Halfway erosional surface that truncates successively older strata to the northeast. Superimposed on the northeastward thinning of Middle Triassic regional isopach trends are local north-south-trending thickness anomalies interpreted as postHalfway block faulting. The combination of post-Halfway erosion and block faulting has resulted in reservoir facies preservation being completely controlled by structure. Based on reconstruction of the geological history, a hydrocarbon exploration model has been developed for the Peejay Field in order to predict the genesis, distribution and degree of preservation of reservoir facies.
Middle Triassic strata of the Peejay field in northeastern British Columbia are composed of four regressive shorefaces, the youngest having been reworked by tidal inlets. Tidal-inlet sublitharenites and bioclastic grainstones form the best reservoir facies. These deposits form a series of shoreline-parallel, narrow, sharp-based, linear sand bodies that eroded the paleoshoreface. The orientation, geometry, and internal sedimentology of these tidal-inlet facies suggest that the paleoshoreline was subjected to a wave-dominated paleohydrographic regime. Determining the processes responsible for forming a specific tidal inlet can provide information regarding waves, tides, and storms characteristic of the depositional setting. Knowledge of this paleohydrographic regime can aid in predicting the orientation and internal characteristics of tidal-inlet reservoir facies. Improved predictability of reservoir facies geometry and quality can have direct implications on hydrocarbon exploration and development strategies of these and similarly formed hydrocarbon plays of the Triassic in the Western Canada sedimentary basin and elsewhere.
Twelve second-and third-order T-R (transgressive-regressive) sequence boundaries have been delineated in the Triassic succession of the Sverdrup Basin, Arctic Canada. Sequence stratigraphic data from six other localities throughout the world, including Svalbard and Barents Sea, Germany, Italy, eastern Siberia, northern Himalayas and the southwestern U.S.A. indicate that these boundaries are global in extent. The ages and orders of these global sequence boundaries are: 1) near Permian-Triassic boundary (2nd order), 2) late Dienerian (3rd order), 3) late Smithian (3rd order), 4) near Early-Middle Triassic boundary (2nd order), 5) late Anisian (3rd order), 6) near Middle-Late Triassic boundary (2nd order), 7) early Carnian (3rd order), 8) mid-Carnian (3rd order), 9) near Carnian-Norian boundary (2nd order), 10) mid-Norian (3rd order), 11) near Norian-Rhaetian boundary (2nd order), and 12) near Triassic-Jurassic boundary (2nd order). All twelve of these high-order boundaries are also readily recognizable in the Triassic succession of the Western Canada Sedimentary Basin. A widespread unconformity is associated with each boundary on the basin margin with a conformable transgressive surface forming the boundary farther basinward. Various potential stratigraphic traps are associated with each boundary. At various localities, the global sequence boundaries commonly exhibit the effects of tectonic uplift and thus tecton-ics was a factor in the generation of these boundaries. To accommodate the combination of both tectonic and eustatic mechanisms in the generation of the global boundaries, it is proposed that they are a consequence of episodic, major plate tectonic reorganizations. During these episodes, changes in spreading rates and/or directions would induce changes in the horizontal stress regimes of the oceanic and continental portions of plates. This would in turn result in an initial eustatic fall and tectonic uplifts along basin margins. During the subsequent relaxation phase, eustatic rise and tectonic subsidence on basin margins would occur. These combined eustatic and tectonic movements would create sequence boundaries consisting of subaerial unconformities and conformable transgression surfaces as well as associated stratigraphic surfaces including ravinements, maximum flooding surfaces and regressive surfaces of marine erosion within stratigraphic successions in many areas throughout the world. RI~SUMI~
Description and illustration of diagnostic pedicle features play an important role in the identification of elasmobranch scales from the Triassic of northeastern British Columbia. Two main types of scale pedicle are recognized, truncate and tetrahedroid. Morphological changes in the scales including pedicle type, pedicle base and margins, and subcrown ornamentation are observed across the Carnian/Norian boundary. The most useful features of Middle and Late Triassic elasmobranch scales from northeastern British Columbia (B.C.) are described, illustrated, and organized into a hierarchy with divisions of part, supergroup, group, and subgroup. A key which can be used to determine scale subgroup is provided.
Regionally extensive core coverage in beds of the lowermost Upper Triassic Charlie Lake Formation - between the "A" marker and underlying Middle Triassic Halfway or Doig beds - in the subsurface of west-central Alberta and adjacent northeast British Columbia facilitate the interpretation of a regional depositional setting. Three broad facies assemblages are identified: 1) red beds; 2) grey beds; and 3) sandstone beds. These three assemblages occur in geographically restricted areas. The red-bed assemblage occurs mostly along the eastern margin of the basin and is interpreted as predominantly intertidal to supratidal, sabkha deposits. The grey-bed assemblage is present between the red-bed and western sandstone assemblages and consists of predominantly intertidal to shallow subtidal beds deposited in a lagoon. Sandstones occur in two locations; in the west they are part of a linear belt, and at the second location they are associated with a local paleogeographic feature, the Beatton High, located within the grey-bed assemblage north of Fort St. John, in northeast British Columbia. The western sandstones are deposits of a barrier-island complex, whereas the sandstones associated with the Beatton High are local tidal channel and fan-delta deposits sourced from the Beatton High. The west-to-east facies changes and north-northwest alignment of the facies define a western, sandy barrier-island complex behind which (to the east) was a lagoon with sabkha deposits at its eastern margin. In the lagoon, a mixture of siliciclastics, carbonates and evaporites were deposited.
Upper Triassic strata in the Trutch (94 G) NTS map area consist of the Charlie Lake, Baldonnel and Pardonet formations. These
units comprise a mixed siliciclastic–carbonate succession, approximately 350 to 400 m thick. Sediments accumulated along a
low gradient continental ramp deposited on the northwestern margin of Pangaea. Twenty-two lithofacies, deposited in distal
offshore through supratidal settings are documented. Seven recurrent facies associations are identified in these strata; four
reflecting deposition in continental to marginal marine settings, and three reflecting shallow to deep water marine deposition.
Facies association 1 (FA1) consists of interbedded dolomitic mudstone/siltstone and dolomitic sandstone that was deposited
in an intertidal flat depositional setting. Facies association 2 (FA2) consists of normally graded, trough cross-bedded to
current ripple-laminated lenticular beds of mudclast-rich fine- to medium-grained sandstone, and was deposited by a series
of small tidal channels. Facies association 3 (FA3) consists of well-sorted fine-grained sandstone beds characterized by high-angle
tabular to wedge-shaped cross-beds, low-angle planar cross-beds, low-relief, translatent ripples and inversely graded lamina
sets. FA3 is interpreted to represent deposition by a series of elongate, shore-parallel aeolian dunes. Facies association
4 (FA4) consists of a heterogeneous succession of solution collapse breccias, rooted, pedogenically-altered mudstone and siltstone,
and wave-rippled very fine- to fine-grained sandstone. It is interpreted as ephemeral lacustrine and/or supratidal sabkha.
Facies association 5 (FA5) consists of variably bioclastic quartzose sandstone, crinoidal packstone-grainstone and bivalve-dominated
packstone beds. It is interpreted as a wave-dominated shoreface to foreshore on a shallow (inner) ramp. Facies association
6 (FA6) is dominated by very fine-grained calcareous sandstone and thin to thick-bedded bivalve-dominated wackestone, packstone
and grainstone. It is interpreted as medial ramp (i.e., offshore transition to proximal offshore). Facies association 7 (FA7)
consists primarily of organic-rich calcareous siltstone and mudstone (commonly with abundant carbonate concretions) and variably
thick tightly packed bivalve packstone/grainstone beds. It is interpreted as outer ramp (proximal to distal offshore).
Siliciclastic sediment in the study area was derived from a variety of sources, including fluvial input from the east-northeast,
longshore drift from the north, and aeolian input sourced from marginal marine dune fields.
Carbonate sediment in the study interval consists primarily of bioclastic detritus, although non-skeletal grains, particularly
faecal pellets, and ooids are locally common. Skeletal carbonate material is dominated by disarticulated mollusc valves and
crinoid skeletal debris but also includes ammonoids, articulate brachiopods, gastropods. Vertebrates (fish and reptiles) are
also common.
Sandstone bodies of the Middle Triassic Doig Formation are composed of well sorted sublithic- to quartz arenites and bioclastic packstones to grainstones deposited in a shoreface environment. These south-southeast trending sandstone bodies were tilted into the Peace River Basin as a result of periodic reactivation of the Dawson Creek Graben Complex and subsequent sediment loading over the southern portion of the reservoir trend. Effective porosity is primarily intergranular in the reservoir sandstone facies, and significant moldic and intragranular porosity is developed in the coquina facies at the West Stoddart and Cache Creek fields. Average porosity ranges from 6.5-9.4% for the sandsone lithofacies and 4.9-8.6% for the coquina lithofacies. Pore-occluding cements are mainly calcite in the northwestern, and dolomite and anhydrite in the southeastern, reservoirs. Sandstone bodies with only minor interstitial calcite have undergone extensive porosity loss due to compaction and authigenic quartz precipitation. A Doig sandstone exploration fairway is identified, based on the following: production, thermal maturity, core analysis data, structural and depositional models, and diagenesis. Reservoir quality and production from Doig Formation sandstone bodies in the Peace River area of Western Canada are impacted significantly by the preservation of intergranular porosity and fractures and by the distribution of early calcite cement. Bioclastic grainstones and packstones and calcareous mudstones were the likely source of calcite for early cements. Diagenetic events along the northwest-southeast reservoir trend include the precipitation of calcite in the near surface and shallow burial realm, the formation of fractures and faults in cemented intervals, and the dissolution of cements and framework grains in three identifiable episodes. Multiple dissolution phases during diagenesis created secondary moldic, intragranular, and intergranular porosity. The formation of open fractures during early diagenesis enhanced both the secondary porosity and the permeability of the West Stoddart and Cache Creek Doig pools. Production data from the Valhalla, Sinclair, West Stoddart, Cache Creek, and Buick Creek fields reflects the control of diagenesis on porosity and permeability.
Three classic sections of Middle and Late Triassic fossiliferous limestones cropping out around Williston Lake in British Columbia, Canada, were sampled for paleomagnetic study. The objective was to test the suitability of these units for detailed magnetobiostratigraphic study with the aim of improving the reference Triassic geomagnetic polarity time scale. The Williston Lake characteristic magnetizations differ, however, from any Triassic North America cratonic reference directions. A satisfactory agreement is found instead with Cretaceous - early Cenozoic North America cratonic reference directions. The exclusive occurrence of normal polarity suggests that remagnetization likely occurred during the Cretaceous long normal superchron. Remagnetizations may have been triggered by connate brines, which moved along aquifers of porous sandstones and carbonates in the early stages of Laramide folding.
Triassic–Jurassic boundary sections on the shore of Lake Williston, British Columbia record a spectrum of depositional environments from the western Canadian continental margin. A primarily deep-water, anoxic record of deposition, indicated by V/V + Ni, V/Cr, Th/U indices and pyrite framboid and facies data, is seen throughout the Late Triassic–Early Jurassic (Norian-Hettangian) interval in a section at Black Bear Ridge. Abundant Monotis bivalve populations in Norian strata are interpreted to have lived on the seabed during transient oxygenation events that punctuated the background anoxic conditions. Monotis went extinct around the Norian/Rhaetian boundary and the deep-water assemblages are subsequently dominated by thin-shelled pectinids. An intra-Rhaetian sea-level fall generated a major hiatus in the proximal Black Bear Ridge section whilst distinctive lowstand strata were developed in the more distal and more complete Ne Parle Pas Point and Pardonet Creek sections. These consist of shallow-water, phosphatic ooid sand facies that contain diverse bivalves. The majority of the infaunal bivalves (but not the epifaunal ones) disappeared at the acme of the regression. This is the end-Triassic mass extinction event and it occurred shortly before a terminal Triassic flooding event. This transgressive event is associated with a rapid negative shift of δ13Corg values interpreted to be the Initial Isotope Excursion of Hesselbo et al. [Hesselbo, S.P., Robinson, S.A., Surlyk, F., Piasecki, S., 2002. Terrestrial and marine extinction at the Triassic-Jurassic boundary synchronized with major carbon-cycle perturbation: a link to initiation of massive volcanism? Geology 30, 251–254]. The Rhaetian record of Williston Lake thus records an extinction of shallow-water infaunal bivalves during a lowstand prior to the development of a transgressive record that is associated with a major, negative C isotope.
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