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Fourth International Conference on Fault and Top Seals
- Conference date: 20 Sep 2015 - 24 Sep 2015
- Location: Almeria, Spain
- ISBN: 978-94-6282-164-4
- Published: 20 September 2015
21 - 40 of 55 results
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Usinskoye Field (Timan-Pechora Province) - Lower Serpukhovian Oil Pools Sealing and Scattering
By E.B. RileThe lower Serpukhovian oil pools of Usinskoye field are exposed to various ways of sealing – by regional anhydrite top seal, by faults. They have also different ways of scattering – through the hydrodynamic window in the top seal, when the anhydrites are replaced with carbonates, or through the gap in the top seal caused by the faults. Faults role is ambiguous – in the case of Usinskoye field they are partly sealing at the anhydrite intervals, and they are not at the carbonate intervals. That is they are increasing or even form oil pools on the uplifted sides because thick anhydrites of the forth bed overlay porous carbonates of the third and destroying oil pools if they are located on the lowered side and come into contact with permeable rocks. In our particular case the faults in general play positive role. The correctness of the hypothesis is verified by correspondence between the discovered controlling object and the level of hydrocarbon-water contact.
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3D Fault Plane Geometry and Fault Scaling Studies Using Seismic Attributes
More LessWe have applied an advanced seismic fault attribute workflow to improve images of faults at different scales. The attribute volumes were used to study the actual geometry of fault plane in 3D in space. This fault plane assessment is independent of uncertainties imposed by traditional seismic-interpretation. We measured fault geometric attributes including fault length, displacement, and height from different seismic fault attributes to study fault-scaling properties. Our study showed that faults are segmented along their length and the number of segments increases towards the upper and lower tips. The distance between fault segments also increases towards the upper and lower tips. Fault length varies almost symmetrically through fault plane and reaches its maximum almost at the center of its extent. The displacement versus depth exhibits a narrow belly-shaped distribution. The depth at which the maximum accumulated displacement occurs does not coincide with the depth where the maximum fault length reaches.
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Characterization of Fault Zones for Reservoir Modeling - An Example from the Illizi Basin, Algeria
Authors L. Mattioni, B. Caradec, L. Jeannin and R.Y. CherifA fault seal analysis was performed in the south-eastern area of the Illizi Basin (Algeria) as an aid to improve reservoir management of this structurally complex region. The objective was to characterize the sealing mechanism, apply modern techniques to evaluate the dynamic behavior of faults in fault-seal analysis, and show how pressure data can be used for calibration with relatively limited subsurface data. The fault sealing analysis was conducted for each of the principal faults and reservoirs in the studied area. The analysis was based on detailed 3D seismic mapping at multiple stratigraphic levels. Intermediate horizons, including non-mapped sands and reservoir bases, were constructed based on the stratigraphy observed in well logs. Data from the already drilled exploration wells provided direct constraints on the stratigraphy in each fault block analyzed. The results of our study show the relevance of this kind of integrated analysis and give a more precise idea of the sealing capacity of faults in the study area of Illizi Basin of Algeria. The methodology could be confidently applied to other prospects/leads within the area to reduce the risk associated to the fault retention.
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Geological Condition and Characteristics for Formation of Deformation Bands - Example from Jizhong Depression, China
More LessDeformation bands mainly developed in high porous rocks whose porosity more than 14.3%. Deformation bands and fissure simultaneously developed in rocks with porosity between 10.1% and 14.3%. In high porous rocks, fault zone has bipartite texture. The fault core has cataclasite features. Deformation bands developed in damage zone. This thesis describes geological condition and characteristics of deformation bands according to well Jin 93-41X which was drilled across fault zone in Shulu Sag. The main controlling factors of the types of deformation bands are clay content and diagenetic stage. In pure sandstones, the grain flow is the deformation mechanism during unconsolidated to semi-consolidated of diagenetic stage, which formed disaggregation bands. Cataclastic bands developed during consolidation of diagenetic stage. In impure sandstones,the phyllosilicate bands formed during unconsolidated to semi-consolidated of diagenetic stage. The features of deformation bands are that the thickness of single deformation bands is several millimeters, and displacement is a few centimeters. They change the physical characteristics of parent rock obviously, and lead to the changes of porosity, permeability and displacement pressure. Cataclastic bands and phyliosilicate bands have the largest reduction in permeability. The changes of physical property promote the heterogeneity of reservoir, which has significant influence on fluid flow.
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Estimating the Coulomb Failure Function Using Seismic Velocities
Authors T. Colson, B. Boterhoven, D. Castillo and M. KeepFault seal capacity is an important component in the conventional petroleum system. Assessing the capacity for a fault to seal or leak can be difficult, particularly where well constraint is lacking. In the frontier basin, in a marine setting, the only data available may be from a seismic survey. However, useful constraints on a faults sealing capacity can be extracted from this data alone. This study investigates the robustness of a number of empirical relations that can assist in extracting useful constraints from seismic velocities. Reliable estimates on maximum and minimum stress tensors and pore pressures can be calculated and combined with basic fault architecture analysis, to aid in placing some practical constraints on fault risk. In this study an area on the Rankin Trend, North West Shelf Australia, found good correlation between well-based and seismic velocity-based pore pressures and stress magnitudes allowing a coulomb failure function based only on stacking velocities to be calculated.
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Characterization and Prediction of Seal Lithological Variability from Log and Seismic Data
By K.D. KurtevAuthor presents an approach for data integration at different scales and for characterisation and prediction of seal properties variations which define seal quality. Presented is an original methodology for seal mud-rich facies recognition from conventional logs and their distribution parameters assignment to the seismic attributes. Sensitivity analysis of the recognition and characterization methods is performed, which allows to quantify seal capacity and its determination uncertainty at seismic scale.
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Geometry, Microstructure and Petrophysical Properties of Compaction and Shear Bands at Silica Dome, Valley of Fire State
Authors A. Torabi, B.E. Jarstø, A. Cilona and S. DengWe characterized and compared shear and compaction bands formed in Aztec Sandstone in Silica Dome, Valley of Fire, Nevada, USA. We investigated various portions of a single sand dune (from bottom-sets to fore-sets), and documented multiple sets of compaction bands and shear bands. We have conducted geometric (length and thickness) and in-situ measurements of permeability and hardness of compaction and shear bands and the surrounding host rock. Microstructural analysis has been performed on thin sections of representative samples to understand and compare the characteristics of shear and compaction bands. Our results confirm that shear bands are longer and thinner than compaction bands in this locality. Density, elastic moduli and permeability of shear bands have a wider range than those of compaction bands. This reflects the heterogeneous microstructures, which relates to different degrees of compaction and cataclasis along the shear bands. Shear bands can reduce porosity and permeability more than compaction bands (in extreme cases), up to two orders of magnitude compared to host rock in this study.
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Growth Juxtaposition Diagrams - A New Angle on an Old Technique
Authors H. Anderson and C. Reilly1D juxtaposition triangles provide a quick way to evaluate across-fault horizon juxtaposition and sealing capacity in the absence of a 3D model. The diagrams are traditionally derived from a single well source and therefore do not incorporate across-fault horizon growth; an assumption which negatively impacts on the accuracy of the modelled juxtapositions. However,constraints on the extent of sedimentary growth is often readily available from secondary wells or adjacent seismic reflection data. Using this data two new types of juxtaposition triangle, “Two-Well” and "Percentage Growth”, can be constructed. Deriving growth data either from a secondary well or as a percentage increase in across-fault thickening, the new techniques are used to model juxtaposition and shale gouge ratio on a kilometre-scale growth fault in the Taranaki Basin, offshore New Zealand. The results indicate that Two-Well and Percentage Growth diagrams provide a more realistic representation of the fault sealing capacity than a 1D solution.
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Filling the Gaps – From Microscopic Pore Structures to Transport Properties in Shales
Authors T. Schäfer, R. Dohrmann, C. Greenwell and M. JensenThe presentation will be the summary of a workshop organized by the NEA Clay Club hold in conjunction with the EUROCLAY 2015 conference in Edinburgh focussing on new method development using electron, x-ray, neutron and laser- based analytical techniques used to characterize porosity, pore size distribution and pore connectivity in compacted clays and tight formations. This data will be discussed in light of molecular dynamic (MD) and 3D pore scale modelling approaches to explain anion and cation transport and mechanical behavior.
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Assessment of Fault-seal Integrity for Underground Storage of Natural Gas in Porous Sandstone
Authors L.D. Meng, X.F. Fu, X.L. Zhang, T.W. Li and J. LiuUnderground gas storage is widely employed for balancing the supply and demand of natural gas, mostly during cold winter periods. We investigate Banzhongbei gas storage (BGS) bounded by B816 and Banqiao fault in Dagang gas storage facilities acting as a swing-supplier to meet peak demand for Beijing, Tianjin and Hebei province. There was wasted natural gas exceeding 7.7×108m³in BGS from 2003 to 2013 that has been one of the most serious problems. There would be big risks on fault-seal integrity. Two aspects included fault membrane seal and fault stability are congsidered in the assessment of fault-seal integrity. We have calibrated the fault membrane seal capacity with the pressure differences across faults from three depressions in Bohai Gulf Basin. Based on that, we conclude that the B816 fault has low lateral capillary sealing capacity resulting in BGS and B814-B to be just one trap bounded by BQ fault. Lateral and vertival membrane seal assessment suggests BQ fault has higher capillary entry pressure (>4.5MPa) than that of stable fault chould sustain (3.0MPa). Hence, according to the stability of BQ fault that the risk of fault seal integrity focus on, modled maximal injection volumn is 13.7×108m3.
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Fault Seal Analysis of a Natural CO2 Reservoir
Authors J. Miocic, G. Johnson, S.M.V. Gilfillan, C.I. McDermott and R.S. HaszeldineFor potential CO2 storage sites it is crucial to know if faults will act as flow baffles or if CO2 will be able to migrate out of the reservoir complex. Geomechanical fault seal analysis for a CO2 reservoirs is very similar to hydrocarbon reservoirs. However, fault rock seals have the potential to act very different in a CO2-rock-water system compared to a hydrocarbon-rock-water system. Natural CO2 reservoirs are common in sedimentary basins world-wide and here we present the results of a fault seal analysis, with emphasis on juxtaposition and fault rock seals, of a natural CO2 reservoir from the Colorado Plateau. The reservoir has leaked CO2 for more than 350 ka along faults. Our results show that the existing gas column can overcome the capillary entry pressure of the fault rocks, leading to migration of CO2 to the surface. Additionally, the fault is orientated favourable for reactivation in the current stress field.
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Predicting Hydraulically Conductive Fractures - A Comparison of Methods
Authors S.A. Weihmann and D. HealyReliable estimation of fracture stability in the subsurface is crucial to the success of exploration and production in the petroleum industry, and wider applications in earthquake hazard, hydrogeology and waste disposal. Being able to predict the stability of fractures in a reservoir (or seal) can enhance recovery and returns. Previous work has suggested that fracture stability is related to fluid flow in rocks: specifically, that more highly stressed fractures tend to exhibit higher rates of fluid flow. Barton et al. (1995) and Ferrill et al. (1999) described positive correlations of fluid conductive properties and ‘active’ fractures in basement rock. This contribution tests the applicability and robustness of the published correlations of stressed fractures and elevated fluid flow by the methods of critically stressed fractures (CSF) and dilatation tendency (Td), by comparing observed intervals of elevated fluid flow to the predicted values of CSF and Td. In this preliminary scoping analysis, the fracture stability of 219 fractures are calculated from wellbore data. Results show that the relationship between active fractures and fluid flow is more complex than described by expressions such as CSF and Td.
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Geometry and Rock Properties Modelling of the Callovo-Oxfordian Claystone from a 3D High Resolution Seismic Cube
Authors B. Yven, M.G. Garcia and A.C. ChabironIn the context of a deep geological repository of high-level radioactive wastes, the French National Radioactive Waste Management Agency (Andra) has conducted, over the past 20 years, an extensive characterization of the Callovo-Oxfordian argillaceous rock in the Eastern Paris Basin. This research has served to demonstrate the feasibility and safety of deep disposal of high-level wastes and intermediate-level long-lived wastes. Today, this research is helping prepare for industrial disposal centre's construction and operation Therefore, the geometry and physical rock properties of the Callovo-Oxfordian claystone formation (COx formation) are required to position the repository, design its shape and numerically simulate its behaviour. This article details the sedimentological background and the results of the geological modelling of the COx formation in the contemplated repository area.
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Mechanical Anisotropy Characterization of the Draupne Formation, North Sea
Authors E. Skurtveit, J.C. Choi, M. Soldal, L. Grande, R. Maurer and P. HorsrudAnisotropy is an important characteristic for the mechanical characterization of shale. Both strength and elastic parameters vary with orientation of material due to the lithological anisotropy in the material. A triaxial test program on varying plug orientation was designed to investigate the mechanical anisotropy in the Draupne Formation. From the triaxial experiments, clear strength anisotropy is observed especially in certain range of orientation. Post-test CT images shows that the strength anisotropy is mainly related to failure in bedding planes. The observed strength anisotropy implies that orientation dependent failure criteria should be considered for realistic geomechanical modelling of seal integrity.
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Pressure-dependent Permeability of Shales
Authors E.H. Rutter, J. Mecklenburgh, R. McKernan and R. TaylorThe matrix permeability of shales is of great importance in determining the behaviour of shale seals and also of shale gas reservoirs. Methods of permeability determination must take into account sensitivity to variations in confining and pore pressures. We seek to establish whether common generic patterns of behaviour exist and to establish their parameters experimentally. Pressure sensitivities of two shales are compared, but the same pattern also applies to others. They follow the general law k = A exp(- g(Pc – a Pp)) (1 + D/ Pp) in which k is permeability, Pc is confining pressure, Pp is pore pressure, A, g, a and D are empirical parameters. g and a describe the sensitivity to confining pressure and pore pressure and variations of k by more than 3 orders of magnitude can occur over the whole reservoir pressure range. Slip (Klinkenberg) flow begins to be significant at gas pore pressures below about 50 bars. Partial fluid saturation leads to a reduction in permeability, and in all cases flow is highly anisotropic. If pressure sensitivity of permeability is not taken into account, reservoir evaluations from well tests will lead to substantial overestimation of original gas in place and likely yield with time.
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Past and Present Permeability, Fluid Flow and Self Sealing in a Marl-limestone Sequence in Northern Switzerland
Authors M. Mazurek, G. Deplazes, P. Marschall and D. TraberThe Effingen Member in northern Switzerland, a potential host formation for the disposal of radioactive waste, has been studied in boreholes and outcrops, with the objective to describe its hydraulic, geochemical and fluid-flow characteristics. The hydraulic conductivity within the sequence of Oxfordian marls and limestones is generally very low, with the exception of a fractured limestone sequence that constitutes a potential lateral flow path. Calcite-celestite veins occur frequently and, in most cases, efficiently seal pre-existing fractures. Geochemical data, in particular 87Sr/86Sr ratios and δ18O values of carbonate, yield contrasting characteristics in veins and rock-matrix carbonate, leading to the conclusion that the veins are externally sourced and document open-system behaviour. Given the fact that even the micrite of the rock matrix was partially recrystallised during this stage fluid infiltration, it is concluded that at some time in the past the formation had a substantially higher permeability than today over an extended period of time and that since then, vein formation, in addition to clay swelling, resulted in an efficient self sealing of the formation, except in the most carbonate-rich beds.
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Experimental Observations of the Flow of Water and Gas along Fractures in Shales and Clay Gouge
Authors R.J. Cuss, J.F. Harrington, C.C. Graham and A.C. GrahamA series of laboratory experiments has been undertaken to determine the flow characteristics in Opalinus clay (OPA) and Callovo-Oxfordian claystone (COx). The flow characteristics are far from simple. For example, in OPA, initial swelling of the fractures reduced fracture flow by one order of magnitude. Shear reduced flow by a further order of magnitude and is an effective self-sealing mechanism. However, continued shear increased flow by over four orders of magnitude possibly due to the formation of new microfractures or due to the interaction of fracture asperities and the opening of conductive channels. The injection of gas had no detrimental effect on the hydraulic properties of the fracture. The gas entry pressure of OPA appeared to remain unchanged by shearing and this suggests shear was not an effective mechanism to reduce fracture gas transmissivity. COx showed considerable hysteresis during an unloading cycle demonstrating that stress history is an important aspect of predicting the flow of discontinuities; whereby flow is more closely related to the maximum stress experienced, as opposed to the current stress regime.
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Fault Seal Analysis Incorporating Shale Smear - Implications for Upscaling
By N.T. GrantA simple 1D model has been built to include shale smear in quantitative fault seal prediction. The model uses well data in much the same way as the familiar triangle diagram. Instead of presenting the results as complex juxtaposition diagrams however, the model uses graphical outputs that focus only on windows in the predicted shale smear envelope. Individual smears are calculated using the shale Smear factor (SSF). The smear envelope is generated by mapping each potential smear onto the fault plane using a probabilistic approach, tied to a range of different shale smear geometries. The results show that the across-fault connectivity is affected by the smear placement model used together with the critical SSF for smear discontinuity. The 1D model also allows the impact of geocellular up-scaling to be assessed. First a high-fidelity layer model is built using the well data. This is then up-scaled to create a blocked model, which is then resampled to derive the equivalent “upscaled” layering. Layer thickness (rather than cell dimension) is an implicit requirement for smear prediction using the Shale Smear Factor (SSF). The 1D model is able to assess the impact of varying geocell dimensions on the fault seal prediction. Whether a fault becomes more or less sealing due to upscaling is a function of the net/gross and stacking pattern of the reservoir and seal layers.
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Permeability Anisotropy in Faulted Sandstone - Implications for Fault Seal
Authors N. Farrell and D. HealyQuantifying the permeability of fault zones and fault rocks is critical to the success of exploration and production. Directional variations in permeability have previously been reported from clay-rich fault rocks, but here we describe significant permeability anisotropy in fault rocks produced from two different sandstones, an arenite and a sub-arkose. In both cases, the maximum permeability of the fault rock is aligned with the fault slip vector in these normal faults, and the minimum permeability is oriented in the fault normal direction. Permeability anisotropy spans 3-5 orders of magnitude in both cases, and has major implications for the prediction of sealing behaviour in the subsurface. While the across fault permeability in our samples is low and the faults might be predicted as sealing, the along fault (up-dip) permeability is so high that leakage along the fault is a real possibility. Our results highlight the need for careful analysis of directional variations in permeability, especially in fault zones and fault rocks.
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Tectonic Control on Cataclastic Strain Distribution and Permeability Reduction in Porous Sandstone Reservoirs
Authors G. Ballas, R. Soliva, H. Fossen and R.A. SchultzWe combine a thorough structural and petrophysical analysis of multiple deformation band sets (France, USA, Germany, Taïwan, Uk) with a broad dataset synthesis of deformation band permeability from the literature. Our analysis first reveals that strain localization in porous sandstones is characterized by fault zones surrounded by sets of shear bands showing a high degree of comminution. In contrast, distributed strain, does so in the form of pervasive and closely spaced compactional shear band and shear-enhanced compaction-band sets, showing moderate and low degree of comminution, respectively. Shear strain localization is inherent to the normal fault Andersonian regime and locations of upward-propagating underlying faults. In contrast, compactional strain distribution is inherent to thrust fault Andersonian regime. A synthesis of band permeability data reveals strong permeability decrease with the increase of comminution, especially in the normal fault regime. This demonstrates a major control of tectonic setting (extension/contraction) on fluid transmissibility of porous sandstones reservoirs containing cataclastic band networks. These results are consistent with a mechanical model proposed earlier based on the analysis of porous granular materials subjected to burial, different stress conditions and material properties.
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