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Discrete fracture network in Santa Rosa Formation according to scenario 1 (A, view southeast; B view looking northwest). Strain legend is as in Fig. 5.
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The integration between kinematic structural restorations and discrete fracture simulation is applied to a thrusted and fractured fault block in the Tarija basin, Northern Argentina. The emphasis is on the influence of the factor time on the deformation history and fracture growth. The structural evolution of the gas bearing Santa Rosa reservoir fo...
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Context 1
... resulting DFN (Fig. 7) shows that most fractures occur in the front limb. The fracture density then decreases over the crest towards the backlimb, according to patterns of the strain map (Fig. 5A). Scenario 1 illustrates the effect of timing of deformation on local strain assessment, but all fractures where assumed to have formed during a single deformation ...
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This work presents a a case study from Bongor basin, Chad which utilizes the geological evolution approach to effectively characterize unconventional granitic reservoir based on the interpretation performed with borehole images and open hole logs. Interplay of fractures and facies and the impact of the prevalent stress regime have been deciphered f...
Citations
... The geomechanical basis of fracture modeling has a wide spectrum. Simple techniques include structural curvature and faulting (Fischer and Wilkerson 2000), strain by structural deformation (Sanders et al., 2004) and superposition of local and regional far field paleo-stress (Ozkaya, 2014). There are also several more sophisticated techniques such as simulated annealing (e.g., Jang et al., 2013;Mahmoodpour and Masihi, 2016), discrete element method (Cundall, 1988) and hybrid finite-discrete element methods (Munjiza et al., 1995). ...
Conductive fractures in petroleum reservoirs may be totally isolated or fully interconnected. There is an intermediate state between the two extremities. Partially fractured reservoirs include finite fracture networks (FFN), which are bundles of interconnected fractures embedded in a sea of isolated fractures. Devising measures for sizes of FFNs is crucial in estimating critical engineering aspects such as productivity index, production decline rate and expected ultimate recovery of wells especially in reservoirs with low matrix porosity and permeability. Here, we present results of statistical evaluation of FFN size in relation to fracture connectivity which is in essence the number of fracture intersections per fracture. The analysis is based on a large number of stochastic 2-dimensional (2D) Poisson models of sub-vertical layer bound fractures. Fracture length in the models has log normal or truncated power distribution and fracture strike has circular normal distribution. The models may have single or multiple fracture sets and various truncation modes with different probabilities.
The analysis shows that number of fracture intersections per fracture can be accurately estimated by a fracture connectivity index, which is defined as product of facture scan-line density, average fracture length and sine of strike standard deviation. The statistically significant finding of this study is that the number of fractures within a FFN is an exponential function of fracture connectivity index. All three fracture properties defining the index can be measured on borehole image logs. Hence it should be possible to estimate fracture connectivity and corresponding FFN size from borehole image data. The analysis pertains to 2D fracture connectivity which is always the lower bound of number of fracture intersections in 3-dimensions. Therefore the exponential relationships must also hold for actual 3-dimensional layer-bound fractures with variable dips.
... 29.2 and 29.3). Anticlines that form at this structural level were generated by fault-bend folding or/and fault-propagation folding, that in many cases have been generated by out-of-sequence thrusts Sanders et al., 2004). This structural level is bounded by the Silurian detachment level at the base (Kirusillas Formation), and a detachment level close to the base of Los Monos Formation at its top (Figs. ...
In this chapter, we present seismic evidence of the interaction between inverted normal faults and reverse faults under the southern Salar de Atacama Basin in the western Central Andes of northern Chile. The chapter starts by presenting a summary of the main tectonic mechanism proposed by several authors to explain the structure of the basin, as well as a regional-scale perspective of the geological context for the region. Then, we present a detailed description of the type of the seismic data used, and the workflow and seismic criteria applied to perform the structural interpretation. We also described the main seismic and geological characteristic of the first-order structural styles recognized in the study area, following the identification of some key stratigraphic and structural elements that finally allowed us to propose the presence of both inverted normal faults and reverse faults. In the last section of the chapter, we propose a tectonic evolution of the study region, considering the interpretations of the different structures previously presented.
... Dowd et al. (2009); Elmo and Stead (2010)) and especially hydraulical flow modelling (e.g. Hyman et al. (2015); Bisdom et al. (2017)) or reservoir modelling (Sanders et al., 2004). According to Pan et al. (2019) a DFN model contains three basic statistical models to represent the 3D discontinuity geometry: an orientation distribution model, a dimension model, and a spatial distribution model. ...
In the course of engineering geological ground characterizations, internal structures of sediments are often simplified to continuous units and structures like lenses are drawn in cross sections based on geologists’ experience. Seeing this as oversimplifications, we propose discrete sediment body (DSB) modelling which is a computational workflow that permits generation of 3D meshes of sediment bodies. DSB modelling can be used to stochastically model highly detailed sedimentary underground structures, based on geometrical assumptions (e.g. size and orientation of lenses) that can be derived from engineering geological investigations. From a geological point of view, the framework is suited to model underground conditions where one would describe the occurrence of chaotic lens-shaped sediments. The modelling process follows a pipeline, where first estimations about the distribution and geometries of the sediment bodies are made. To get non-intersecting meshes as a final product, surrogate point clouds are generated that follow the initial geometrical estimations, which are then clustered, and finally alpha shape based meshes are generated around the clusters. Resulting 3D sediment bodies enable easy generation of consistent 2D geological cross sections and can be used as a basis for further analyses. The paper is finished with a case study where a finite element stability analysis is done for a slope excavation with underground conditions featuring clayey silt lenses in a matrix of gravelly sand. It can be shown that the lenses substantially influence the ground behavior in comparison to a classical approach with continuous units.
... Stochastic Discrete Fracture Network (DFN) modeling is a technique used to represent the natural heterogeneity of the geometrical features of the fracture network and to estimate its subordinate petrophysical properties (Darcel et al., 2003;Park and Lee, 2003;Min et al., 2004;Botros et al., 2008;Maillot et al., 2016). DFN models are not only useful to support civil engineering, but also to define the predominant fluid pathways in fracture-dominated groundwater aquifers, and oil and gas carbonate reservoirs (Rouleau and Gale, 1987;Parney et al., 2000;Svensson, 2001;Maréchal et al., 2004;Sanders et al., 2004;Follin et al., 2014;Klammler et al., 2016;Fang et al., 2017;Hadgu et al., 2017;Xu et al., 2018). The quantification of fracture network connectivity is needed to solve multiple problems related to the geothermal environment: define the geometry of the geothermal fields and to calculate the heat transference (Watanabe and Takahashi, 1995;Lee et al., 2018), improve wells connectivity and enhance geothermal reservoirs (Doe et al., 2014;Aydin, 2000Aydin, , 2018, and perform stimulation essays at production stages (Fu and Carrigan, 2012;Gan and Elsworth, 2016), among others applications. ...
... This can be accomplished by quantitative geomechanical methods and kinematic structural restorations (i.e. Sanders et al., 2004;Watkins et al., 2015;Ukar et al., 2016) but this was beyond the scope of the present study. Also, the poor quality of the available 3D seismic data, and the complexity of structural deformation and erosion of Eocene-Miocene sedimentary rocks in the area, precluded such a detailed analysis. ...
Identifying controls on the permeability of fluid‐conductive fractures is critical in tight reservoirs, but this is challenging in tectonically complex regions such as foothills belts where there may have been multiple stages of deformation and fracturing. Fracture permeability depends on fracture aperture and connectivity, both of which are affected by tectonism and cementation. Among the many factors that control the cementation history, oil charging may play an important role. Important challenges in studies of fractured reservoirs in tectonically complex regions include determining the timing (and intensity) of fracturing events relative to that of the oil charge, verifying the presence of matrix storage, and establishing the fracture cementation history.
This paper reports on a comparative fracture study of four small‐scale oilfields in the west Adıyaman Basin, located within the foothills belt of the Tauride suture zone in SE Turkey. Here the tight reservoir carbonates of the Sayındere Formation (Campanian) were subjected to repeated phases of structural deformation. Major deformation phases took place in Campanian and Maastrichtian times, before oil charging into the reservoir began in the Eocene; and in the Late Eocene – Oligocene and Late Miocene, after the oil charge. Fractures that were generated before oil emplacement appear to have been cemented or partially cemented by calcite as indicated by cross‐cutting cemented fractures on borehole images. Partially‐cemented fractures in cores are oil‐stained with cement‐lined walls, suggesting cementation began before oil emplacement but was not completed. Image logs and cores also show the presence of clean, open fractures with no cement present on the walls. These open fractures cut across the cemented or partially‐cemented fractures, and are in general related to Late Miocene compressional folding. Open fracture density is correlated to Late Miocene fold curvature and asymmetry in the four oilfields studied. Of these fields, the Șambayat structure is the tightest and most asymmetric anticline and hence has the maximum open fracture density; this field also has the highest oil potential.
Although the available data is not sufficient to evaluate the effects of oil charging on fracture cementation definitively, the observations are consistent with a model that oil charge into the fractured Sayındere Formation carbonates inhibited or slowed calcite cementation. Hence fracturing of a carbonate reservoir after oil emplacement may significantly enhance the fracture permeability, and may even render a tight reservoir prospective.
... Various geomechanical and statistical methods are available for predictive modeling of dispersed fractures (Olson et al. 1998;Dershowitz et al. 2000;Sanders et al. 2004;Lefranc et al. 2014;Guo et al. 2016;Macaulay et al. 2016;Marrett et al. 2017;Su et al. 2017). Predictive modeling of fracture corridors is relatively less common and usually uses seismic attributes, such as lineaments (Neves et al. 2004), coherence cube or curvature (Roberts 2001;Chopra 2002;Chopra and Marfurt 2007;Gao 2013), seismic attributes combined with reservoir simulation (Bourne et al. 2000;Questiaux et al. 2010), or structural/geomechanical modeling of faults and fractures along faults (Laubach et al. 2014;Duriez et al. 2016;Liu et al. 2017). ...
A challenge in oil-reservoir studies is evaluating the ability of geo -mechanical, statistical, and geophysical methods to predict discrete
geological features. This problem arises frequently with fracture corridors, which are discrete, tabular sub-vertical fracture clusters. Fracture corridors can be inferred from well data such as horizontal-borehole-image logs. Unfortunately, well data, and especially borehole image logs, are sparse, and predictive methods are needed to fill in the gap between wells. One way to evaluate such methods is to compare
predicted and inferred fracture corridors statistically, using chi-squared and contingency tables.
In this article, we propose a modified contingency table to validate fracture-corridor-prediction techniques. We introduce two important
modifications to capture special aspects of fracture corridors. The first modification is the incorporation of exclusion zones where
no fracture corridors can exist, and the second modification is taking into consideration the fuzzy nature of fracture-corridor indicators
from wells such as circulation losses. An indicator is fuzzy when it has more than one possible interpretation. The reliability of an indicator
is the probability that it correctly suggests a fracture corridor. The indicators with reliability of unity are hard indicators, and
“soft” and “fuzzy” indicators are those with reliability that is less than unity.
A structural grid is overlaid on the reservoir top in an oil field. Each cell of the grid is examined for the presence and reliability of
inferred fracture corridors and exclusion zones and the confidence level of predicted fracture corridors. The results are summarized in a
contingency table and are used to calculate chi-squared and conditional probability of having an actual fracture corridor given a predicted
fracture corridor.
Three actual case studies are included to demonstrate how single or joint predictive methods can be statistically evaluated and how
conditional probabilities are calculated using the modified contingency tables. The first example tests seismic faults as indicators of
fracture corridors. The other examples test fracture corridors predicted by a simple geo-mechanical method.
... Recently, structure restoration methods, used by structural geologists to check the consistency of the subsurface structural interpretations, have been extended to predict areas that have undergone large strains and to relate the strains to structural heterogeneities such as faults and joints (Hennings et al., 2000;Sanders et al., 2002Sanders et al., , 2004Kloppenburg et al., 2003). Nonetheless, as for the previous techniques to model fractures, geometric restoration does not consider rock deformation as a physical phenomenon. ...
... Conventional workflows for modelling permeability in fractured reservoir models can be based on extracting geometrical distributions from outcrops for stochastic Discrete Fracture Networks (DFNs) and upscaling to effective properties, where seismic-scale variability in fracture patterns is constrained by considering the resultant structural geometries and implications of kinematic and mechanical forward models (Sanders et al., 2004;Shackleton et al., 2009;Bond et al., 2013;Watkins et al., 2015;Ukar et al., 2016). Subseismic trends in fracture network geometry on permeability have been studied in outcrops, both with and without matrix flow, albeit without application to DFNs (Odling, 1997(Odling, , 2001Odling et al., 1999). ...
... Shackleton et al., 2005;Laubach et al., 2009;Savage et al., 2010;Lamarche et al., 2012;Awdal et al., 2016). Folding and faulting are typically considered as the main fracturing drivers, which has resulted in well-defined methods for modelling fractures related to those mechanisms (Sanders et al., 2004;. However, fractures can be commonplace in rocks that experienced no or limited seismic-scale deformation, and although this is recognised qualitatively 1 3 Tavani et al., 2011;, there is a limited understanding of the quantitative relation between regional events such as shortening and burial on the one hand and fracturing on the other hand (e.g. ...
... Syn-folding fracturing has been studied extensively in outcrops (Price, 1966;, as understanding the multiscale relation between seismic-scale folding and subseismic-scale fracturing allows for extrapolation of 1-D well data to 3-D fractured reservoir models (e.g. Sanders et al., 2004;Makel, 2007). Price (1966) presented the first conceptual model for fold-related fracturing, variations of which are still commonly used (e.g. ...
... Syn-folding fractures are modelled using curvature maps or kinematic restorations (e.g. Olson, 1997;Ericsson et al., 1998;Ormand and Hudleston, 2003;Sanders et al., 2004;Wilkins, 2007;Ukar et al., 2016), but these methods do not consider pre-folding deformation. Furthermore, kinematic restorations require a complete understanding of the kinematic evolution of structures and are not suited for more complex deformation related to for example ductile evaporite movements. ...
... As a consequence, new surface and volume restoration applications are continuously emerging, such as Geosec_3D, Kine_3D and the structural modeling workflow implemented in the Gocad application (Moretti et al., 2006(Moretti et al., , 2007Moretti, 2008). Furthermore, 3D restoration methods have been used to study strain distribution (Plesch et al., 2007b;Guan et al., 2012;Li et al., 2013), as well as the kinematics of folds or thrusts (Sanders et al., 2004;Maerten and Maerten, 2006). ...
Three-dimensional (3D) modeling and restoration are powerful in describing the geological characteristics and kinematics which cannot be fully accomplished by the two-dimensional modeling methods. In this study, we applied 3D modeling and restoration to the Beisantai anticline along the mountain front of the Northern Tianshan. The Beisantai anticline shows an EW-trending structure in the shallow layers with NS-trending structures in the deep layers. The 3D seismic reflection data visualize the growth strata well, which record the evolution of the anticline and the influence of Cenozoic India-Asian collision. Our results suggest that a combination of multiple deformations of this anticline on different layers developed during different episodes. In addition, multiphase deformation and strain distribution along the eastern part of the northern Tianshan was implied. Combined with an analysis of the burial and hydrocarbon-generating history from borehole data, we proposed new potential exploration areas in this region and multistage tectonic effects for hydrocarbon accumulation. This work not only highlights our understanding of the structural decomposition of a multiphase structure associated with growth strata, but also the structural evolution of the northern Tianshan and the adjacent petroleum-producing Junggar Basin.
