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EARTH SCIENCES (472 journals)

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Journal Cover Petroleum Geoscience
  [SJR: 0.604]   [H-I: 41]   [6 followers]  Follow
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 1354-0793 - ISSN (Online) 2041-496X
   Published by Geological Society of London Homepage  [10 journals]
  • Introduction to the thematic set: Fault and top seals
    • Authors: Dewhurst, D. N; Yielding, G.
      Pages: 1 - 1
      Abstract: The 4th EAGE Conference on Fault and Top Seals was held in Almeria in SE Spain from 20 to 24 September 2015. A total of 118 delegates attended (78 from industry, 21 from academia and 19 students). The conference provided the opportunity to learn about the latest advances in seal evaluation and the increased scientific rigour behind the technologies employed as we begin to understand more about the basin- to pore-scale processes that trap hydrocarbons. The same workflows are also readily adapted to studies for geological storage of carbon dioxide (CO2) and nuclear waste.
      PubDate: 2017-02-01T06:59:38-08:00
      DOI: 10.1144/petgeo2016-303
      Issue No: Vol. 23, No. 1 (2017)
  • Linking capillary and mechanical seal capacity mechanisms
    • Authors: Underschultz J. R.
      Pages: 3 - 9
      Abstract: Mechanical fault reactivation is a mechanism where high fluid pressures generated within a fault zone can change the effective stress such that an optimally orientated fault segment will rupture. This style of strain has been recognized in three settings: (1) deep crustal locations at greenschist and higher-grade metamorphism with fluid generation; (2) active plate boundaries where tectonic stresses can result in seismicity; and (3) hydrocarbon column buoyancy pressure reactivation of critically stressed fault-bound traps. This paper examines category 3 in the context of mechanical fault reactivation and capillary processes. For water-wetting fault rock, mechanical reactivation may be reached prior to the capillary seal capacity. However, the non-wetting fluid cannot access the fault rock pore space until the hydrocarbon column height reaches the capillary threshold pressure. At the threshold pressure, the non-wetting fluid enters the fault rock imparting a buoyancy pressure in excess of the mechanical reactivation threshold causing rupture. This suggests that in certain circumstances the mechanical fault reactivation by buoyancy pressure is more accurately predicted by the capillary threshold pressure than mechanical reactivation pressure.
      PubDate: 2017-02-01T06:59:38-08:00
      DOI: 10.1144/petgeo2016-032
      Issue No: Vol. 23, No. 1 (2017)
  • Relationships between bright amplitudes in overburden rocks and leakage
           from underlying reservoirs on the Norwegian Continental Shelf
    • Authors: Simmenes, T. H; Hermanrud, C, Ersland, R, Georgescu, L, Sollie, O. C. E.
      Pages: 10 - 16
      Abstract: Identification of the locations where hydrocarbon traps leak is of significant practical importance, especially if the leakage controlled the present-day fluid contacts. We have investigated the fluid contacts of five structural traps offshore Norway that are dry or underfilled, and which have apparently had larger hydrocarbon columns in the past. The main focus of our work was to apply observations of bright amplitudes in overburden rocks in order to identify the most likely positions for vertical leakage, and to compare and contrast these observations from different parts of the Norwegian Continental Shelf.It was seen that bright amplitudes were present in overburden rocks above likely leakage locations in all of the investigated structures. The bright amplitudes line up along fault planes in some of the traps and, in other cases, are clustered along fault intersections. The leakage-related brights were only noted in parts of the overburden sequences, presumably because most of the overburden rocks did not have sufficient permeability to host the gas quantities that are needed for seismic imaging. We conclude that analyses of overburden brights above likely leakage locations can contribute to improved prediction of hydrocarbon–water contacts in the subsurface.
      PubDate: 2017-02-01T06:59:38-08:00
      DOI: 10.1144/petgeo2016-093
      Issue No: Vol. 23, No. 1 (2017)
  • The impact of faults and fluid flow on seismic images of a relay ramp over
           production time
    • Authors: Botter, C; Cardozo, N, Lecomte, I, Rotevatn, A, Paton, G.
      Pages: 17 - 28
      Abstract: Relay ramps can act as conduits for fluid flow in producing hydrocarbon reservoirs, but the two bounding faults are often at the limit of seismic resolution. To study the impact of relay ramps and their fluid composition on seismic data, we present an integrated workflow combining flow simulation in a geomodel of an outcrop relay ramp, forward seismic modelling and seismic-attribute-based volume extraction. In the chosen outcrop of the Arches National Park (Utah, USA), the petrophysical properties are conditioned by deformation bands present in the sandstone, and are used to run a simple water injector–oil producer fluid-flow simulation. Pre-stack depth-migration seismic images are obtained at t = 0, t1 = 10 and t2 = 20 years of the flow simulation. The seismic image porosity changes at t = 0 when the model is oil-saturated, whereas the water–oil contacts have stronger amplitude contrasts at later stages. With an adapted attribute-based workflow, we are able to extract geobodies corresponding to the faults and the relay ramp from the three seismic cubes. By varying workflow parameters, we also show reservoir and acquisition conditions that can affect the resolution of the relay ramp on the seismic image either positively or negatively.
      PubDate: 2017-02-01T06:59:38-08:00
      DOI: 10.1144/petgeo2016-027
      Issue No: Vol. 23, No. 1 (2017)
  • Risking fault reactivation induced by gas injection into depleted
           reservoirs based on the heterogeneity of geomechanical properties of fault
    • Authors: Meng, L; Fu, X, Lv, Y, Li, X, Cheng, Y, Li, T, Jin, Y.
      Pages: 29 - 38
      Abstract: Predictions of fault reactivation and the hydraulic seal of cap rock are integral parts of the seal integrity research programme of the Banzhongbei gas storage facility (BGS) to ensure the safe storage of natural gas in subsurface reservoirs. We attempt to combine the heterogeneity of geomechanical properties, including frictional coefficient and cohesive strength, into a workflow to estimate fault reactivation risk and the maximum sustainable fluid pressure that will not induce failure of trap-bounding faults and cap rock. Based on the Griffith – Coulomb Failure criterion, fault failure modes – including tensile failure, shear failure and hybrid failure – may occur under conditions of the same in situ stress field as a result of the strength heterogeneity of fault rocks, which plays a key role in the estimation of integrity of the entire fault trap. The juxtaposition of the seal on the BQ Fault with high shale gouge ratio (SGR) values makes a significant contribution to the high fluid pressure build-ups during gas injection, and its low strength properties lead to a higher reactivation risk for the Banqiao (BQ) Fault than for the B816 Fault. The increased pore-fluid pressure adjacent to the BQ Fault induced by gas injection should be lower than 9.7 MPa in order to avoid failure. Furthermore, the maximum sustainable fluid pressure of the cap rock is approximately 13.9 MPa at the locations of the injection wells.
      PubDate: 2017-02-01T06:59:38-08:00
      DOI: 10.1144/petgeo2016-031
      Issue No: Vol. 23, No. 1 (2017)
  • A geometrical model for shale smear: implications for upscaling in faulted
    • Authors: Grant N. T.
      Pages: 39 - 55
      Abstract: A new 1D bed-scale model has been built to help model shale smear in interbedded sand–shale sequences using the shale smear factor (SSF). A smear envelope is generated by mapping each potential shale smear onto the fault plane employing five different shale smear geometries. Graphical outputs then focus on the cumulative length of the resultant smears and the remaining sand–sand juxtaposition windows in the predicted shale smear envelope. The smears are evaluated stochastically with lengths that are a randomized function of the estimated Vclay content of the source shale layers, allowing the smear pattern to change with each realization. A new fragmented smear mode is developed that allows discontinuous smears to be distributed randomly on the fault plane and can be used to modify the smear pattern as fault displacement increases. The model has been tested using well data. Results show that windows in the smear envelope are commonly present, and that their frequency and location are dependent on the smear placement model and sand–shale stacking pattern. Smear fragmentation leads to more windows being preserved. The 1D model can also assess the impact of geocellular upscaling on fault seal analysis. Upscaling reduces cross-fault sand connectivity due to the elimination of thin beds. Shale smear envelopes are also reduced in length as fewer shale beds are involved, even though layers are thicker. A fault may or may not appear more sealing dependent on the layer configuration and net-to-gross ratio (NTG). The model offers results that can inform input to fault seal evaluations and allows the effect of geomodel upscaling to be more closely interrogated.
      PubDate: 2017-02-01T06:59:38-08:00
      DOI: 10.1144/petgeo2016-021
      Issue No: Vol. 23, No. 1 (2017)
  • Trap Analysis: an automated approach for deriving column height
           predictions in fault-bounded traps
    • Authors: Bretan P.
      Pages: 56 - 69
      Abstract: Column height predictions are often displayed as attributes on fault-plane profiles. However, fault-plane profiles are difficult to interpret when derived from multiple faults that bound a trap. An automated approach, termed Trap Analysis, permits the rapid analysis of column height predictions using the deterministic fault-seal analysis method.For column height predictions to be meaningful, all faults that contribute to the sealing of hydrocarbons within a trap must be analysed as one coherent structural element. Hydrocarbon column height data at key reservoir juxtapositions on all faults that bound a trap are simultaneously interrogated to derive the unique location of the weakest point on the fault seal, termed Fault Leak Point (FLP). The FLP is trap-critical if it supports a column with a contact that is shallower than the trap's structural spill point.The Trap Analysis approach enables sensitivity studies to be routinely undertaken. The predicted weakest point on a fault seal, and hence, the column height supported at that point, can depend on the calibration used to transform shale gouge ratio (SGR) to threshold capillary pressure, and on the density contrast between the buoyant and water phases.
      PubDate: 2017-02-01T06:59:38-08:00
      DOI: 10.1144/petgeo2016-022
      Issue No: Vol. 23, No. 1 (2017)
  • Toward the creation of models to predict static and dynamic fault-seal
           potential in carbonates
    • Authors: Solum, J. G; Huisman, B. A. H.
      Pages: 70 - 91
      Abstract: In contrast to faults in clastic reservoirs, rules to predict the exploration and production timescale fault-seal potential in carbonates are lacking. This paper provides a summary of carbonate reservoirs with cross-fault column height differences that represent examples of apparent static fault seal, and a summary of observed examples of dynamic fault seal in carbonate reservoirs and aquifers. These include cross-fault differences in water table depths across carbonate–carbonate juxtapositions, cross-fault pressure differences in carbonate aquifers separated by faults, production-induced cross-fault pressure differences in carbonate hydrocarbon reservoirs, sealing behaviour of faults in carbonate reservoirs inferred from well tests, and examples of low fault transmissibilities from history-matching exercises from carbonate reservoirs. This paper also documents the range of compositions of fault rocks in carbonates and the range of permeabilities that have been reported from low-permeability fault cores in carbonate fault zones, as well as the implications of the observed range of fault permeabilities in carbonates for sealing behaviours. The purpose of this paper is not to argue that every fault in a carbonate reservoir will seal or will even be capable of sealing. There are, however, enough examples of faults in carbonates that are sealing in a dynamic sense, and in a static sense, that the topic of carbonate fault seal should warrant much more study. Creation of predictive models will ultimately require a considerable amount of subsurface data, but these models should be created.
      PubDate: 2017-02-01T06:59:38-08:00
      DOI: 10.1144/petgeo2016-044
      Issue No: Vol. 23, No. 1 (2017)
  • Fault reactivation in travertine and its impact on hydraulic
           transmissibility: laboratory experiments and mesoscale structures
    • Authors: Giwelli, A; Esteban, L, Delle Piane, C, Clennell, M. B.
      Pages: 92 - 103
      Abstract: Direct shear experiments were undertaken to investigate the effect of faulting and reactivation on the hydromechanical characteristics of faults in continental carbonate samples. The tested rock is a travertine of continental, microbial origin with a calcite content of 99 wt%, with a strongly laminated texture. Analyses of the intact and sheared samples performed using medical X-ray computed tomography (CT) revealed that the porosity is mainly composed of subplanar pores and vugs. Permeability is high along the laminations, controlled by interconnected pores and fractures. The travertine is a lithological analogue for Aptian pre-salt oil reservoir rocks found in South Atlantic offshore basins. Three samples, with dimensions of 240 x 110 x 150 mm, were sheared to a maximum displacement of 120 mm under different levels of effective vertical stress (6–45 MPa), resulting in the formation of cataclastic fault gouge surrounded by a dense fracture network. A new experimental method was used to reactivate the artificially formed fault by performing cyclic vertical loading at different shear displacements on a previously sheared sample, while keeping a constant pore-pressure differential throughout the test.Pore-fluid responses across the fault zone were monitored continuously during both deformation (dynamic transmissibility) and hold periods (static transmissibility). Results show that the transmissibility reduces in all the samples for all values of the applied effective vertical stress and during shear reversal. The static transmissibility also decreases over time, which may be a result of creep deformation or the blocking of pore channels with gouge material. Our results indicate that once the gouge material is developed in the core of a carbonate fault zone, the dynamic transmissibility across that fault is permanently decreased, with little dependence on subsequent kinematics of reactivation, or changes in stress, so long as the gouge zone is not breached by a new structure.
      PubDate: 2017-02-01T06:59:38-08:00
      DOI: 10.1144/petgeo2016-025
      Issue No: Vol. 23, No. 1 (2017)
  • Do deformation bands matter for flow? Insights from permeability
           measurements and flow simulations in porous carbonate rocks
    • Authors: Rotevatn, A; Fossmark, H. S, Bastesen, E, Thorsheim, E, Torabi, A.
      Pages: 104 - 119
      Abstract: We investigate the permeability and flow effects of deformation bands in porous granular carbonate rocks in Malta and use results from flow simulations to discuss the practical implications of deformation bands in carbonate and siliciclastic reservoirs rocks in general. Image- and laboratory-based analyses of deformation bands show permeabilities that are 1 – 2 orders of magnitude lower than the adjacent host rocks. Small-scale outcrop-based flow models (1 x 1 m) focus on the effect of deformation band on flow at the scale of individual bands. Two-phase flow simulations (water displacing oil) show that at the local scale a decrease in deformation band permeability led to increasing flow complexity, reduced and irregular waterfront propagation and reduction in sweep efficiency. A reduction in host rock permeability is associated with increased sensitivity to deformation bands. In low-permeable host rocks, a single magnitude-order reduction of deformation band permeability significantly delays flow, whereas in higher-permeable host rocks the effect is less pronounced. Hence, in some cases, deformation bands may represent a significant impediment to flow already when they are only 1 – 2 orders of magnitude less permeable than host rock. Consequently, deformation bands may have greater practical implications than previously thought, particularly in reservoir rocks with moderate to low host rock permeability.
      PubDate: 2017-02-01T06:59:38-08:00
      DOI: 10.1144/petgeo2016-038
      Issue No: Vol. 23, No. 1 (2017)
  • The value of fault analysis for field development planning
    • Authors: Frischbutter, A. A; Fisher, Q. J, Namazova, G, Dufour, S.
      Pages: 120 - 133
      Abstract: Faults play an important role in reservoir compartmentalization and can have a significant impact on recoverable volumes. A recent petroleum discovery in the Norwegian offshore sector, with an Upper Jurassic reservoir, is currently in the development planning phase. The reservoir is divided into several compartments by syndepositional faults that have not been reactivated and do not offset the petroleum-bearing sandstones completely. A comprehensive fault analysis has been conducted from core to seismic scale to assess the likely influence of faults on the production performance and recoverable volumes. The permeability of the small-scale faults from the core were analysed at high confining pressures using formation-compatible brines. These permeability measurements provide important calibration points for the fault property assessment, which was used to calculate transmissibility multipliers (TM) that were incorporated into the dynamic reservoir simulation model in order to account for the impact of faults on fluid flow. Dynamic simulation results reveal a range of more than 20% for recoverable volumes, depending on the fault property case applied and for a base case producer–injector well pattern. Fault properties are one of the key parameters that influence the range of cumulative recoverable oil volumes and the recovery efficiency.
      PubDate: 2017-02-01T06:59:38-08:00
      DOI: 10.1144/petgeo2016-053
      Issue No: Vol. 23, No. 1 (2017)
  • Faults as barriers or channels to production-related flow: insights from
           case studies
    • Authors: Wibberley, C. A. J; Gonzalez-Dunia, J, Billon, O.
      Pages: 134 - 147
      Abstract: This paper presents case studies of producing fields where faults heavily influence fluid-flow behaviour. In a first case, faults show no evidence of barrier behaviour prior to production but, nevertheless, demonstrate strongly compartmentalized field behaviour once production starts. Analytical modelling suggests that short-term pressure differences between faulted panels can be predictable owing to the permeability contrast between fault zone and reservoir: fault permeability, however, is not low enough to prevent dissipation on the geological timescale. Faults in a second case acted as baffles during production, supporting significant pressure differences, with salinity data suggesting that, as a network, they channelled sweep through relays and around fault tips. The third case examines a fault acting as a vertical drain, causing early water breakthrough through proven intermediate seals and depleting non-produced aquifers above. The fault permeability required to explain these depletion rates is estimated from an analytical model. Estimates of 0.02 – 0.2 mD compare well with predictions from a new algorithm calibrated using measurements on natural fault rocks from seismic-scale faults. Experience from case studies such as these can improve the way in which we use limited data from exploration wells when considering fault behaviour in development scenarios and in conditioning reservoir models for production forecasting.
      PubDate: 2017-02-01T06:59:38-08:00
      DOI: 10.1144/petgeo2016-057
      Issue No: Vol. 23, No. 1 (2017)
  • The transmissibility of faulted connections in corner-point geometry
    • Authors: Islam, M. S; Manzocchi, T.
      Pages: 148 - 158
      Abstract: The transmissibility expression generally used for connections across faults in industrial flow-simulation models built using corner-point geometry is inaccurate, because of cell misalignments across the faults. A comprehensive suite of high-resolution flow-simulation models has been designed to assess the magnitude of the error, which is greatest for connections with smaller juxtaposition areas; between cells with higher kV:kH ratios; between cells with greater length: height aspect ratios; in more heterogeneous sequences; for connections containing more permissive fault rocks; and for connections between cells with lower angular misalignments. Transmissibility can be underestimated by a factor of 10 or more in the absence of fault rock; however, the inclusion of realistic fault transmissibility multipliers virtually eliminates the error. The expression for transmissibility for corner-point geometry models contained in commercial simulators is therefore within acceptable limits for most realistic faulted full-field models.
      PubDate: 2017-02-01T06:59:38-08:00
      DOI: 10.1144/petgeo2016-033
      Issue No: Vol. 23, No. 1 (2017)
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