- Home
- Conferences
- Conference Proceedings
- Conferences
3rd EAGE International Conference on Fault and Top Seals
- Conference date: 01 Oct 2012 - 03 Oct 2012
- Location: Montpellier, France
- ISBN: 978-90-73834-35-4
- Published: 03 October 2012
21 - 40 of 68 results
-
-
Discrete Element Modeling of Friction of Sand-clay Mixtures
More LessThis paper presents a preliminary study on the effect of the clay content on the mechanical properties of the fault gouge materials using the discrete element method (DEM). It is also a feasibility study to examine how numerical modeling based on the DEM can be used to predict the hydro-mechanical properties of the fault. 2-dimensional (2D) models were used. The sand and the clay particles were explicitly mimicked using mixed two groups of elements with different sizes and different mechanical properties. Simulations of biaxial compression tests were performed, and the friction coefficients of the models with different clay contents were calculated from the simulation results. The modeling results were compared with some published laboratory experimental results. They agreed qualitatively. This study therefore demonstrates that a simple 2D DEM model can qualitatively capture the effect of the clay contents on the mechanical properties of the sand-clay mixtures. However, further studies are expected to be done in order to quantitatively predict the hydro-mechanical parameters of the fault gouge materials using DEM modeling.
-
-
-
Developing a New Algorithm for Calculating Fault Seals within the Structural Model
Authors P. Røe, H. Kjønsberg and T. BarkveTraditionally fault seal calculations take place directly within the simulation grid. This approach works well for grids where all the faults are aligned along the grid pillars, but implementing an algorithm that works with stair-stepped representation of the faults has proven to be very difficult. Especially the calculation of the displacement field used both indirectly in the fault seal parameter calculation and directly in the calculation of fault zone permeability is challenging. It is hard to find where the different grid layers intersect the fault trace, and the layers are not always completely represented on both sides of the fault. We present a novel algorithm where the calculation of the fault zone permeability is carried out on a 2D plane representing the fault surface. The input parameters needed for calculating the fault zone permeability are resampled from the simulation grid onto the 2D plane, while the resulting fault zone permeability is resampled back into the simulation grid, prior to calculation of the fault transmissibility. The new approach is shown to generate good results both for pillar-faulted grids, and for grids with stair-stepped faults, and also works well near complex truncations.
-
-
-
Methods to Evaluate and Predict the Effects of Extreme Reservoir Compartmentalization, BNA Reservoir, Canada
Authors P.J. Vrolijk, R. Skelly, S.E. Bradley, A.C. Ostridge, N. MacCallum and J. WoodReservoir compartmentalization; fault compartments; production pressure histories; engineering data; subsurface flow; fault seal; fault network; fault baffle; fluid flow modeling Presentation will integrate geologic interpretation methods (including uncertainty) of a complexly faulted reservoir with subsurface fluid flow and pressure histories to constrain oil and water flow between fault block compartments
-
-
-
Fault Core/damage Zone; an Unhelpful Description of Fault Zone Structure?
Authors C.J. Childs, T. Manzocchi, J.J. Walsh and M.P.J. SchopferThe standard outcrop description of fault zones currently in vogue is a high strain fault core containing fault rock surrounded by a low strain halo termed a damage zone. This description does not acknowledge the significance of fault segmentation or displacement partitioning within fault zones and therefore fails to capture features which are crucial for defining the flow charateristics of faults. This terminology derives from outcrop studies but it is limited in it's ability to describe faults in 3D. Outcrop studies can best contribute towards an understanding of fault zones if they are set in the context of an appropriate 3D appreciation of faults, including quantitative definition of internal displacements and strain. Fault terminology should be guided by those datasets where 3D fault zone structure can be deciphered rather than by what is convenient in outcrops where it cannot. We suggest that the damage zone/fault core description promotes not only a simplified view of faults, but also a misleading one which is an obstacle to understanding them.
-
-
-
Permeability of Fault Rocks and Shale Caprocks: Where we Stand
Authors Q.J. Fisher, C. Grattoni, J. Haneef and M. ShahMuch published fault rock permeability data was measured using inappropriate laboratory conditions (low confining pressure and distilled water as the permeant). However, the results are reasonably consistent with theoretical predictions from simple clay-sand mixing models. This may suggest that the effects low confining pressures (increases permeability) and distilled water (reduces permeability) to a certain extent cancel each other out. The results from the mixing models suggest that the permeability of the sand end-member may have an important control on the permeability of fault rocks. This model helps explain the large scatter on Vclay-permeability cross plots but is not considered by existing fault seal algorithms. Techniques used in the shale gas industry for estimating permeability are not appropriate for use in measuring the permeability of shale caprocks. The lack of a rapid decline in permeability as a function of porosity of measurements made on low permeability shale core plugs as well as inconsistent relationships between pore-throat size and permeability, suggests perhaps that techniques using core plugs overestimate the permeability of low porosity (<15%) shales by several orders of magnitude. It is likely that this reflects the inability of current techniques to accurately measure permeabilities significantly below 1nD.
-
-
-
Testing Fault Seal Prediction Algorithms Using Geomodels of Experimentally Produced Fault Zones
Authors B.N. Ciftci, S.B. Giger and M.B. ClennellGeometries of clay smears produced in a series of direct shear experiments were analyzed and related back to the monitored hydraulic response, the deformation conditions, the clay content and the strength contrast between the seal and reservoir rock. The sheared blocks were imaged by CT scanning that was interpreted to construct geomodels of the fault zones from which quantitative information was obtained. The distribution of smears varies according to the level of stress during the shearing and to the contrast in brittleness of layering. Brittle clay layers form more segmented seals while ductile soft clays form more diffuse smears.Fault drag and tapering of the smear is limited to the fault cut-offs contrasting the predictions of CSP model. Increased normal stress improved fault sealing by increasing fault zone width, which led to more clay involvement in the fault zone. The average clay proportion of the fault conforms to the prediction of the SGR model. However, the hydraulic seal performance doesn’t correlate to the SGR but the net clay volume in the fault zone.
-
-
-
Diagenetic and Tectonic Evolution of Pore Networks in Carbonate Normal Fault Zones and their Effects on Permeability
Authors T.J. Haines, E.A.H. Michie, J. Neilson, D. Healy, G.I. Alsop, N. Timms and A. AplinThis study quantifies changes in carbonate fabrics and pore network characteristics in fault zones using field analogues with the ultimate aim of understanding fluid flow around carbonate hosted normal fault zones. The shallow water carbonate sequence in Malta, which is dissected by an array of normal faults of varying displacements, is the chosen field analogue. The study reveals a wide range in petrophysical properties on the core plug scale. Porosity ranges from less than 5 % to greater than 35 %, permeability varies by seven orders of magnitude from 0.001 mDs to 1000 mDs and ultrasonic p-wave velocity ranges between 2 and 6 km/s. The range in these petrophysical properties is in part due to primary depositional fabric. However, modifications of the primary fabric during subsequent diagenesis and deformation are important in shaping the petrophysical properties of the rock. Pore throat size and pore type are important characteristics of the pore network which control the permeability. The changes in the carbonate fabrics into fault zones results in pore throat size and pore type changes and hence modifies the permeability. Total porosity and rock fabric are important controls on the p-wave velocity and can allow for predictions of pore network characteristics.
-
-
-
Cataclastic Deformation Band Formation
Authors A. Nicol, C. Childs and J.J. WalshArrays of closely spaced (1-5 mm) sub-parallel cataclastic deformation bands are a common feature of faults in high porosity sandstones. The distribution of strain onto many low displacement bands is generally thought to require strain hardening within the deformation bands. This strain hardening model does not however account for widespread coalescing deformation bands and appears to have little support from laboratory data. The geometries and locations of many zones of deformation bands point to the role of fault geometrical complexities, rather than mechanical properties, in the formation of clusters of deformation bands. The geometric model is principally one of slip localisation by removal of fault surface irregularities and fault-rock weakening, a mechanism which is generally accepted for fault-zone development during brittle deformation for rock types other than high porosity sandstones.
-
-
-
Strain Localisation in Porous Sandstone as a Function of Tectonic Setting, Burial and Material Properties
Authors R. Soliva, G. Ballas, R.A. Schultz, A. Taboada, C. Wibberley, E. Saillet and A. BenedictoThe analysis of three cataclastic band sets from Provence (France) reveals that the band density, their conjugate angles, their ratio of shear displacement to compaction, and the amount of cataclasis are different and can be expressed as a function of tectonic setting and petrophysical properties. We identify (1) a dense and closely spaced network of shear enhanced (reverse) compaction bands, (2) a regularly spaced less dense network of reverse compactional shear bands, and (3) a localized network of normal shear bands. The field data show that the localization of strain is favored in an extensional setting and is characterized by shear bands with a large shear to compaction ratio and a low conjugate band angle. In contrast, distributed strain is favored in a contractional setting and is characterized by compactional bands with a low ratio of shear to compaction and a large conjugate band angle. To explain the mechanical origin of this strain localization, we quantify the yield strength and the stress evolution in extensional and contractional regimes. We propose a model of strain localisation in porous sandstone as a function of tectonic stresses, burial depth, material properties, strain hardening and fluid pressure.
-
-
-
The Role of Cataclasis in Shear and Compaction Bands on Water Flow in Porous Sandstone, Provence, France
Authors G. Ballas, R. Soliva, J.P. Sizun and A. BenedictoDetermination of membrane seal capacity of deformation bands is a critical problem for the managing of the geologic reservoirs in porous sandstones. In this study, we describe the geometry, the microstructure and the petrophysical properties of two sets of deformation bands: (1) a set of shear enhanced compaction bands and (2) a set of shear bands. At the microscopic scale, the image analysis porosities and the grain size distributions allow us to define three different types of microstructural deformation: crush microbreccia, protocataclastic, and cataclastic. Cataclastic strands are characterized by a porosity reduction of 10% to 25% and permeability reduction of 3 to 5 orders of magnitude compared to the host rock. Field observations of iron hydroxide precipitations around the bands suggest that only cataclastic shear bands were membrane seals to water flow under vadose condition. This study therefore highlights the importance of the degree of cataclasis in deformation bands as membrane seals to subsurface fluid flows in sandstone reservoirs.
-
-
-
Deformation Mechanisms in Uncemented Sandstone, Examples from Triaxial Tests
Authors E. Skurtveit, A. Torabi, R.H. Gabrielsen, R. Alikarami, G. Ballas, H. Fossen and R. SolivaDeformation mechanisms in porous sandstone and sand are important for understanding the distribution of faults and their associated properties. Controlling mechanism during localization depends on stress history, burial depth and fluid composition, but also lithological variations like porosity, grain size and mineralogy. An experimental program is design to investigate the pressure conditions and mechanical constrain on localization of deformation structures with varying confining pressure in uncemented sandstone. A natural sandstone material from the Boncavaï quarry in Provence, France, where deformation structures are observed, has been selected for the tests program. In the experiments shear enhanced compaction and cataclasis are identified whereas identification of deformation bands is difficult.
-
-
-
Integrated Containment Analysis - Wiki-accessible Workflows and Tools for Exploration Top and Fault Seal Analysis
Authors P.S. D'Onfro, R.R.D. Treverton and O.A. JokanolaA seal analysis knowledge-base, accessible on the ConocoPhillips Wiki, was created to codify ConocoPhillips' knowledge of fault and top seal analysis practices in a form that has longevity, can be easily updated and that can be easily accessed by exploration geoscientists. The purpose of the knowledge-base,when combined with classroom and field training, is to help sustain in the exploration community a reasonable and realistic level of self-sufficiency with fault and top seal analysis. With the creation of the knowledge-base, ConocoPhillips has established a corporate "best practice" for seal analysis that includes this knowledge-base, a group of centralized experts, a network of distributed practitioners, globally-available vendor-provided analysis tools, and a portfolio of classroom and field training resources.
-
-
-
The Use of Internally Consistent Models in Seal Analysis
Authors H.M. Nordgård Bolås, C. Hermanrud, P. Brockbank, J.R. Eide, R. Heggland and G.M.G. TeigeSeal presence is required for hydrocarbons to be accumulated, and the quality of the seals will often directly determine the fluid contact levels and hence the trapped hydrocarbon volumes. It is therefore crucial that a proper seal analysis always is included in prospect evaluation. A complete seal analysis includes evaluations of both cap rocks and faults. Sometimes also bottom and side seals need to be evaluated. Various tools and methods for evaluating several of these aspects of seal analysis exist. Despite this, an overall work procedure that describes how all the individual tasks of seal analysis should be integrated and prioritized is currently not readily available to the explorationist. Through recent research and case studies we have experienced that it is difficult to apply a standardized work flow for seal analysis. This is so because the relevance of the individual tasks commonly included in such analysis will vary significantly between different areas and between individual traps. However, we have found that the concept of “Internally Consistent Models” (ICM) can be very useful for such analyses regardless of the geological setting. The use of such models will aid integration and provide a basis for risking hydrocarbon volumes in prospect evaluation.
-
-
-
Delineation of Petroleum System Using Faults and Associated Gas Chimneys
Authors M.A. Raza and W.I.W.B. YusoffUnlike other geological techniques and phenomenon for the identification of fault behavior and defining the petroleum system, this study deals with the delineation of faults and gas chimneys for understanding the petroleum system present. Both of these features are self sufficient for achieving the objective. Gas chimneys can provide great information about source, migration path and the accumulation area. Faults carry a vital importance; they can restrict the hydrocarbons in a place by their sealing behavior or act as a conduit for the passage of fluids. Understanding the faults behavior from the gas migration and associated features provides an extra dimension with accurate results. These features are worth studying as they provide information about migration path and helps to define the petroleum system.Faults may act as preferred pathways for fluid migration when permeability of the fault or fault segments becomes higher than the surrounding country rocks.
-
-
-
High Resolution Fault and Seals Imaging from Geological Model - A North Sea Case Study
More LessA new workflow to enhance seals and faults from the seismic imaging is proposed. Whereas most of the proposed methods for the characterization of seals and faults are obtained from seismic attributes, we have used a novel method based on a geological modeling from the seismic. From this model, new kinds of attributes can be derived to enhance sequence stratigraphy, faults, seals and traps. By computing the vertical derivatives of the geological model, also called the "Thickness" cube, it reveals the instantaneous variations of the geological layers in the volume on each seismic voxel. It is sensitive to the convergence and divergence of the geological horizons and therefore appears to be particularly well adapted to reveal traps, seal, spatial distribution of reservoirs. The fault imaging is obtained from the computation of 3D derivatives of the geological model, which shows a detailed detection of faults even in zones with a low signal noise ratio. Applied on the block F03 in the North Sea, this method has proven to be fast and efficient to evaluate prospects for well placement application and also maximize chance of success in exploration.
-
-
-
Improved Fault Imaging by Integration of Frequency Decomposition and Fault Attributes, Example from Mid Norwegian Sea
By B. AlaeiSeismic attributes have been utilized to enhance identification and mapping of faults on seismic volumes. Application of 3D seismic attributes together with advanced visualization techniques allow combination of different fault characteristics and result in a better understanding of complex fault systems. In this study fault attribute analysis is integrated with frequency decomposition process. A fault imaging workflow including structurally oriented semblance attribute volume and fault enhancement attribute volumes have been generated using two different sets of seismic input. First the fault imaging workflow was carried out using full band seismic volume. Then, seismic data has been decomposed into amplitude volumes representing individual frequencies. The same fault imaging was repeated using amplitude volume from high frequency. Amplitude volumes of higher frequencies correspond to higher resolution. The method has been tested on a 3D dataset from the Mid Norwegian Sea. The results show that using amplitude volumes of higher frequencies can image smaller scale faults that are not visible using full band seismic volumes as input for the fault imaging. Improved fault imaging achieved using this method can help derisk fault seal related issues in areas with complex structural setting such as the one presented in this study.
-
-
-
Integrated Reservoir Connectivity Analysis, Zechstein Carbonate Reservoir, Northern German Basin
Authors F.V. Corona, J. Neble and K. RettenmaierAn integrated workflow is presented for evaluating static and dynamic connectivity of a complex Upper Permian Zechstein carbonate reservoir, mainly platform facies, in the Scholen Concession of the Northern German Gas Basin. Sour gas production in the concession involves drainage from multiple, tectonically emplaced and, in places, vertically stacked allochthonous Zechstein carbonate reservoir sections. These allochthons lie within the Permian Zechstein salt and overlie the in-place autochthonous Zechstein reservoir. The key issues in the Scholen Concession are the static connectivity and fill-and-spill scenarios among the multiple Zechstein sour gas accumulations and the dynamic connection between the autochthonous and allochthonous reservoir intervals. Understanding these issues is important in the evaluation of infill drilling opportunities and near-field appraisal wells, and whether or not these opportunities can be drilled safely and economically. The integrated reservoir connectivity analysis incorporating geoscience and reservoir engineering data revealed that the five main gas accumulations in the concession appear to be connected statically through a common aquifer and the in-place autochthon and most detached allochthons likely are connected dynamically with baffles. These learnings ultimately led to realistic and reliable evaluations of infill opportunities and near-field appraisals in the concession area, and changes to the drill-well inventory seriatim.
-
-
-
Comparing Simulated Production Response Across Realistic and Seismically Forward Modelled Fault Geometries
Authors A.M. Wood, R.E.L. Collier and D.A. PatonOutcrop examples show us that reservoir scale faults often have complex geometries, both in cross section and in three dimensions. This complexity may take the form of multiple slip planes, entrained lenses of host material, drag structures and relay zones, however the limitations of seismic data prevent much of this detail from being resolved and incorporated into geological and reservoir simulation models. By forward modelling the predicted seismic response of detailed fault geometries we are able to compare realistic fault architectures to those which can be identified in seismic datasets. In turn, by constructing reservoir simulation models, we are able to assess the impact of these different geometries on predicted hydrocarbon recovery. In certain situations differences in modelled cross fault juxtapositions and calculated fault rock properties between the realistic and forward modelled fault geometries result in significant variations in the simulated production response.
-
-
-
Quantifying the Impact of Fault Damage Zones on Reservoir Performance
Authors D.E. Wolf, J.G. Solum, J.P. Brandenburg and S.J. NarukThis study quantified the contribution of a damage zone for a range of observed host rock and damage zone characteristics, such as: reservoir Vshale; fault shale-gouge ratio (SGR); damage intensity; and permeability of reservoir, fault, and deformation bands. A hypothetical reservoir was utilized to show the impact of a damage zone on the overall FTM calculation. The relative impact of a damage zone on the total cross-fault flow was calculated empirically relative to the percentage of reservoir offset. Single variables were modified in each calculation to isolate the greatest controls on damage zone impact. The calculations were made for a single hypothetical reservoir unit, surrounded by shale above and below. Fault permeabilities were calculated using equations similar to those in Manzocchi et al. (1999). Effective permeabilities were calculated using a harmonic mean. The difference between cross-fault FTM from only the fault core versus the fault core acting with a damage zone was calculated, and used to assemble risking tables to be assessed for a range of Vshale and percentage of reservoir offset. The difference represents the correction factor to be applied to the currently calculated fault transmissibility multiplier (FTM).
-
-
-
A Multi-Disciplinary Workflow for Characterising Shale Seals
Authors D.N. Dewhurst, M.B. Clennell, I. Burgar, M. Josh, J. Sarout, C. Delle Piane, L. Esteban, M. Pervukhina and M.D. RavenEvaluation of the various rock properties of shales has become more prevalent in recent years although our understanding of these properties and the links between them is still relatively embryonic. While thick shale sequences can form sealing units above hydrocarbon traps, intra-reservoir shales can form baffles to flow in both petroleum and groundwater contexts. High field and low field nuclear magnetic resonance were used to evaluate wettability of shales. Preserved shales show mineral dependent variations in surface affinity for oil versus water. Hydrophilic shales have a higher cation exchange capacity (e.g. shales rich in illitic and/or smectite), whereas kaolinitic mudrocks are potentially hydrophobic and can be wetted preferentially by oil, sometimes retaining oil on the mineral surfaces after further exposure to brines. Porosity and cation exchange capacity correlate well with strength properties and dielectric constant measurements on intact shales and pastes made from powdered shales show strong relationships between high frequency electrical properties, mineralogy, cation exchange capacity and mechanical strength. Calibrating wireline logs with laboratory measurements and the development of physics-based models allows the prediction of rock properties and extrapolation to the borehole scale.
-