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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
51 - 68 of 68 results
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Palaeo-fluid Flow History of an Extensional Fault System from Carbonate Concretions in Shallow Marine Sediments, Italy
Authors F. Balsamo, D.R. Gröcke and F. StortiWe present a multidisciplinary study on the relationships between the structural architecture of an extensional fault system in poorly lithified shallow marine sands and the associated pattern of diagenetic carbonate concretions. Based on their shape, spatial distribution, cement texture and chemistry and isotopic signature, carbonate concretions are grouped into (i) tabular concretions developed within the fault zones, and (ii) elongate and coalescent strata-bound concretions formed adjacent and mostly parallel to fault zones. Tabular concretions formed during early diagenesis in the vadose mixing marine-meteoric zone, possibly during coseismic rupture propagation and, in the interseismic periods, due to slow capillary suction along the low-permeable fault zones. On the other hand, elongate concretions formed after regional uplift and during telodiagenesis by precipitation from meteoric, phreatic water flowing parallel to the fault zones which acted as hydraulic barrier. The concretion patterns record the evolution of fluid flow orientation and the changing chemistry of fault-zone fluids that were fundamentally driven by the the fault zones architecture during two major diagenetic stages.
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Mapping of Regional Potential Leak Paths
Authors K.A. Beintema and D.E. EdwardsThis study was aimed at derisking several Jurassic prospects situated in the Central North Sea. Prior to this study, reservoir presence was thought to be the main risk. The structural history of the area is very complex, with an interplay of extension, salt tectonics and sediment deposition. The stratigraphic and structural frameworks together determine the reservoir and seal risks of prospects within the Jurassic sequence. This study comprises of a combined stratigraphic-structural analysis on reprocessed seismic, and has revealed that the interaction between tectonics and sedimentation leads to seal risks not previously identified. This study shows that in the area of interest, potential leaks paths exist connecting Fulmar prospects and Kimmeridge Mass Flows by both top seal erosion and juxtaposition of thief sands across faults.
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Fluid Flow Effects of Faults in Carbonate Reservoirs, an Example from the Kharyaga Field, Russia
Authors O.P. Wennberg, J.I. Logstein and N. HashemiFaults in carbonate reservoirs may have a dramatic effect on fluid flow and represent a major uncertainty in hydrocarbon exploration and reservoir characterization since they are often associated with high permeability conduits as well as potential barriers. The fluid flow properties result from a combination of mechanical and diagenetic processes controlled by the brittle and reactive characteristics of carbonate rocks. The Late Devonian reservoir in the Kharyaga Field of the Pechora Basin is extremely heterogeneous due to fractures and karstification superimposed on the depositional heterogeneity. Faults and open fractures strike dominantly E-W, and the data indicate that fracture density tends to increase towards faults and is associated with decreasing porosity in the matrix rocks. Dissolution and karstification is commonly associated with the faults and fractures. The best and most realistic match of historical production data was achieved when the faults in the simulation models were represented as conduits for flow parallel to the fault and barriers for flow perpendicular to the fault. Geologically this is explained by: a cemented cataclastic fault core representing the barrier, and by a fault damage zone consisting of a connected open fracture network enhanced by dissolution producing high permeability parallel to the fault.
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An Improved Method for Generating Fault Zone Grid
Authors D. Qu, P. Roe and J. TverangerFaults are volumetric in nature and can cause complex fluid flow inside the fault zone because of its special fault zone architecture and different petrophysical properties from the host rock. Thus explicit fault zone modeling is important for capturing the fluid flow inside and through the fault zone precisely. Generation of a refined volumetric fault zone grid is the first step to perform explicit fault zone modeling. An algorithm for generating volumetric fault zones has already been implemented in Havana, however this algorithm failed to generate continuous top and bottom surfaces for the fault zone. This lead to internal discontinuities in the fault zone grid, and made it hard to run flow simulations on the grid. We now present an improved version of the algorithm that works well on complex faults and indicate the capability of explicit fault facies modelling of real field cases.
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Comparison of Mechanical and Fracture Stratigraphy between Failed Seal Analogues
Authors E.S. Petrie and J.P. EvansThe presence of discontinuities in a seal affects both their mechanical and hydrogeologic properties; migration of fluids or gas through mm- to cm-scale discontinuity networks can lead to the failure of gas or fluid traps. The presence of discontinuity networks increases the volume of rock matrix in contact with subsurface fluids creating preferential pathways for fluid flow and changing the mechanical properties of the seal. We examine the mechanical and fracture stratigraphy of failed seals analogues exposed in central and south-east Utah. We use outcrop surveys to identify relationships between occurrence of discontinuities and sedimentologic variability, and to understand the nature of alteration associated with fluid flow through these fractures. We use data from each locality to quantitatively define mechano-stratigraphic units, based on consistency in fracture distribution, bed thickness, lithologic stacking pattern, field-derived compressive strength and permeability. These data allow us to define mechano-stratigraphic units at each locality and to compare the changes in deformation behaviour between localities. Using this systematic methodology to quantify differences and similarities between field analogues we improve our understanding of the important role of micro- to meso-scale fracture networks play within sealing lithologies and how various seal lithologies respond the changes in stress.
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Statistical Analysis of Fault Attributes
Authors D. Kolyukhin and A. TorabiThe statistical analysis of fault attributes scaling relationships is discussed. Dependences of length, width of damage zone and thickness of fault core on displacement were studied assuming power-law relations. The approximation forms a piecewise-linear function with few slopes in log-log scale. The Bayesian Information Criterion (BIC) was used to find the best fit for an optimal number of parameters. Numerical tests show that the best fit was obtained when using power-law relations with two slopes. Bayesian analysis of model parameters’ probability distribution was performed. The second part of this work is devoted to statistical analysis of single faults' attributes. Truncated power-law (TPL) is considered in comparison with commonly used simple power-law (PL) (or Parreto) distribution. The maximal likelihood and the confidence interval of the exponent for both PL and TPL are estimated by appropriate statistical methods. Kolmogorov-Smirnov (KS) test and likelihood ratio test (LRT) with alternative non-nested hypothesis for exponential distribution are used to verify the statistical approximation. Our results suggest that a truncated power-law is more suitable for describing fault attributes and its condition is satisfied for a wide range of fault scales. Furthermore, advantage of TPL is proved by BIC.
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Deformation of Poorly Consolidated Sanstone in Aghione Formation, Corsica, France
By A. TorabiDeformation of poorly consolidated sandstone and its effect on petrophysical properties of the rock are investigated by structural fieldwork, in-situ measurements of permeability, microstructural analyses of thin sections and ultrasonic measurements of samples. The studied locality comprises a series of listric normal faults that cut through Aghione Formation (Miocene) in Corsica, France. Three types of deformation bands are reported. Surprisingly, intense cataclasis is observed in the phyllosilicate-rich (more than 20%) poorly consolidated sandstone. Permeability decreases up to two orders of magnitude in the damage zone (deformation bands), while it increases in the slip surfaces. The slip surfaces are open and make conduit to fluid flow, which is also confirmed by the field observation of fluid flow path.
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Cross Faults - A Major Control on Lateral Compartmentalization of Hydrocarbon Reservoirs of Kuwait
Authors N.M.A. Nada Al-Ammar, R. Husain, S.A. Azim, A. Prakash, R. Mulyono, A. Al-Khamis, P. Singh and R. AndrianySignificant variations in production behavior of the hydrocarbon reservoirs were observed in Kuwait. Understanding of these variations is of vital importance for exploration and production of hydrocarbons. In a synergistic approach, geological, gravity, magnetic, seismic, geochemical and production data were integrated to decipher the reservoir behavior by understanding the structural architecture and role of faults in reservoir compartmentalization. Significant variation in initial reservoir pressures and oil properties across the major cross faults are suggestive of their sealing nature. These faults have developed after the peak oil migration from the Jurassic and Cretaceous source rocks.
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Fault Sealing Behaviour in Three North Sea Reservoirs Estimated from Petrophysical and Production Data
By A.D. IrvingAlthough understanding their flow behaviour is imperative for successful reservoir development, seismically resolvable faults are rarely sampled by wells. Their properties must be extrapolated from imperfect analogues or inferred from dynamic data and numerical reservoir simulation. Published methods regard fault transmissibilities as unknown tuning parameters with consequently limited predictive capability; workflows have therefore been developed for uncertainty assessment and conditioning to dynamic data of geologically consistent fault properties. This paper focuses on their application to three North Sea cases in which simulation models were able to reproduce observed field behaviour using fault properties consistent with core data. In contrast to published correlations between depth and reduced fault permeability, the interpreted permeability in the shallowest field was approximately one order of magnitude lower than for the other two, deeper reservoirs. Within the calculated ranges for Shale Gouge Ratio, the interpreted fault permeability functions for all three fields are within the prior uncertainty range estimated from analogue core data and are consistent with published studies. These functions add significantly to the number of available curves calibrated to sub-surface pressure data and could therefore be of considerable use for prediction of fault behaviour in similar fields without production data.
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Patterns of Clay Mineral Transformations in Fault Gouges
By S.H. HainesNeoformed clay minerals in fault rocks in the brittle crust are increasingly recognized as being key to the sealing behaviour of faults . Academic literature has recognized the importance of neoformation of clay in fault gouge for a number of years, but the concept has not reached most industry seal analysis workflows. Clay-rich gouges that form as a consequence of new clay mineral growth are distinct from clay smears or cataclastic fault rocks that form as a result of mechanical incorporation of wall-rock phyllosilicates, in that they form by chemical and not physical processes. We report a comprehensive field study of clay mineralogy on fault rocks from sedimentary basins and low-angle normal faults in the American Cordillera. We then synthesize the field study with a literature survey to identify controlling conditions for neo-formed clay in fault gouge. Neoformed mineral in gouges are illite, illite/smectite, smectite, and chlorite/smectite phases. Chlorite and kaolinite do not form as neoformed clays in fault gouges. Controlling conditions are wallrock chemistry, temperatures of ~60-180 C and fluid availability.
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The Impact of Aquifer/Caprock Morphology on CO2 Storage in Saline Aquifers
Authors S.M. Shariatipour, G.E. Pickup and E.J. MackayThe CO2 storage project at Sleipner has shown that the topography of the aquifer/caprock interface can have a significant effect on the migration paths of CO2 in an aquifer (Singh et al 2010). Therefore when appraising any reservoir or aquifer for CO2 storage, it is important to characterise the interface and to ensure that it is modelled adequately. Often simulations assume a sharp boundary smooth between the aquifer and the caprock. However studies of outcrops show that a variety of types of interface may arise in nature, depending on the depositional setting. For example, Shariatipour et al (2012) have shown that there may be a gradual transition from sand-rich facies in the aquifer to mud-rich facies in the caprock. Syversveen et al, have investigated the impact of top-seal morphology on CO2 storage capacity and migration patterns, and concluded that it is important to model geological details in order to predict CO2 migration. We intend to investigate different types of caprock/aquifer interface to determine how these affect the pressure build-up under the caprock and the amount of CO2 which dissolves in brine. This will enable us to identify which type of aquifer/caprock has the greatest potential for storing CO2 securely.
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The Role of Vertical Mechanical Heterogeneity in Predicting Fault Zone Architecture
Authors R.K. Davies, R.J. Knipe and M.J. WelchThe modeling of flow across faults in reservoir simulation and in exploration is based often on the permeability distribution. Detailed observations of faults across a range of stratigraphic facies, however, show that this simplification is likely to miss some of the fault zone architectural complexity that can play a significant role in the modeled flow. With over 10 years mapping the details in fault zones from a range of different tectonic and stratigraphic environments, RDR has compiled a unique set of observations that show the importance of the vertical mechanical heterogeneity (VMH) at the time of deformation. In our model for fault evolution, we define an incipient shear zone across which the layers and multilayers are sheared by brittle faulting and ductile folding. This incipient shear zone has been defined as a premonitory shear zone (PSZ) that “forecasts” the position of a fault with discrete offset. The complexity of the fault zone increases with an increase in the VMH with both discrete fault offsets and smearing of the ductile layers. A simple fault zone develops with a lower VMH. These conceptual models, combined with mechanical modeling, describe the process, which improves the prediction of the fault zone architecture.
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Fault Seal and Trap Analysis, High Temperature High Pressure (HPHT) Central North Sea
Authors J.T. Summers, S.J. Naruk, S. Thackrey, J. Solum and D. WolfFault seals seen in the HPHT area of the CNS are generally very good, possibly because of overpressures that, globally, appear to enhance fault sealing, and also because of the nature of Triassic and Jurassic stratigraphy in the area. The various laterally extensive and coherent shales within the Skagerrak Formation as well as the Jurassic Formations are helpful in creating a competent seal along fault planes. Seven of the nine fields also have reservoir-reservoir juxtaposition along fault planes above the hydrocarbon water contacts and appear to be sealing due to SGR. The workflows described here should be applied to future studies with the understanding that the uncertainties in stratigraphy and structure need to be incorporated to receive the best assessment of accumulation controls.
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Field Example of Application of Dynamic Fault Seal Analysis Technology and Well Test Matching to Condition Full Field Reservoir Models
Authors K.O. Onyeagoro, A.B.J. Smout and T.J. WellsQuantification of cross-fault flow and fault transmissibility multipliers is important for the development decisions, since the nature of hydrocarbon and water flow across faults will influence well counts, well placement, and ultimate recovery. The Corrib gas field discovered in 1996 lies 70 km offshore west of Ireland in 360 meter water depth. It is a faulted 4-way dip closure (Figure 1). Within the Sherwood Sandstone, extensional faulting with cataclastic fault rocks is the dominant expression of deformation. Two dominant fault families are present; one set dipping to the east and the other to the west. These faults mainly strike in NE-SW direction. Second generation ESE-WSW striking faults developed at a later stage of deformation probably as a result of sudden change in curvature and stress/strain states at the northern and southern flanks of the structure. This paper discusses workflows to determine Corrib field fault properties, and well test matching workflows to determine reservoir properties and condition dynamic models. The integration of results from fault seal analysis and well test matching deliver significant business impact and demonstrate the value of Shell’s in-house fault seal dynamic modeling capabilities.
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34% of Newly formed Phyllosilicates within Faults of Deeply Buried Sandstones Reservoir
Authors T. Cavailhes, R. Soliva, P. Labaume, C. Wibberley, J.P. Sizun, C. Gout, D. Charpentier and M. BuatierIn this study, we describe normal fault zones cutting foreland arkosic turbidites in deep diagenesis conditions (200°C). The microstructural analysis of the fault cores reveals a large amount of phyllosilicates (up to 34%) in the fault rock, derived from an intense feldspar muscovitisation. This process is favored by mechanical disaggregation of the feldspar grains following cleavage planes during deformation. Point-counting on thin sections sampled in the studied fault zones allows to quantify the proportion of feldspar transformed in white micas between 60-80%. We propose a modified version of the predictive Shale Gouge Ratio algorithm in order to integrate the proportion of phyllosilicates resulting from feldspar muscovitisation. We discuss the importance of feldspar alteration within faults of the deep brittle crust and its role on fault strength and high temperature reservoir partitioning.
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North Oman Fault Geometries in Outcrops, Analogues and Sub-surface and their Implication on Fault Seal
Authors P.D. Richard, L. Bazalgette and M.H.N. Al-KindyNorth Oman offers an opportunity for making outcrop observations of faults developed in carbonate reservoirs. It is possible to examine faults and associated damage zones in great detail, both in map view and cross sections. From these observations, geometrical concepts and rules can be defined. These help to interpret faults on seismic as well as to build static models. It is also possible to demonstrate the potential impact of the simplifications inherent to the static modelling process and to decide whether they are acceptable or not to define the most suitable modelling strategy. The understanding and the modelling of the fault sealing properties are an important part of this process. The main objective of this paper is to share how we can take advantage of the North Oman outcrops, in combination with a database of sandbox analogue models and high quality seismic data, in order to develop conceptual geometrical models of faults. These can be used as a foundation to 3D fault frameworks and to address static and dynamic fault seal properties. The conceptual geometrical models are also used to develop interpretation and modelling strategies, as well as workflows for the elaboration of geo-cellular models designed for specific recovery mechanisms.
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Modelling of Relay Ramp Using Fault Facies and Truncated Gaussian Simulation
Authors M. Fachri, A. Rotevatn and J. TverangerRelay ramps may considerably control fluid flow across otherwise sealing fault zones and, therefore, they are subjected to fluid flow simulation studies in relation with groundwater extraction and petroleum production. However, these studies used mainly deterministic modelling approach based on field observations. In this paper, we extend this approach by incorporating a conditional simulation technique, i.e. truncated Gaussian simulation (TGS), to provide stochastic elements in the modeling work and to improve the representation of detailed relay ramp structure. TGS attributes (facies proportions and variogram ranges of the Gaussian field) are defined based on field observations of the Delicate Arches Ramp, Utah, which is characterized by the presence of three structural sets. Groups of facies defined based on the structural sets are modelled independently using TGS, and the final model is generated by merging the TGS realizations. The relay ramp facies model is used to generate upscaled models. The upscaling procedure use petrophysical values and coarse grid used in a recent flow simulation study of the Delicate Arches Ramp deterministic model. Flow simulation results show that the role of relay ramp as conduits for fluid flow is more pronounced in models built using TGS than that in deterministic models.
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The Quantification of Fracture Patterns
By D. HealyFractures in deformed rocks are rarely uniform or random. Fracture orientations, sizes, shapes and spatial distributions often exhibit some kind of order, or pattern. In detail, there may be relationships among the different fracture attributes e.g. small fractures dominated by one orientation, larger fractures by another. This is important because the mechanical (e.g. strength, anisotropy) and transport (e.g. fluids, heat) properties of rock depend on these fracture patterns and fracture attribute relationships. This presentation describes a methodology to quantify fracture patterns, including distributions in the fracture attributes and their spatial variation. There is a large body of published work on the quantification of relatively simple joint patterns, but fault zones present a bigger, and arguably more important, challenge. The method presented is inherently scale independent, and a key task will be to analyse, interpret and integrate quantitative fracture pattern data from micro- to macro-scales.
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