Fault Interpretation During Seismic Interpretation and Reservoir Evaluation
M.E. Badley, B. Freeman, A.M. Roberts, J.S. Thatcher, J. Walsh, J. Watterson, G. Yielding, 1991. "Fault Interpretation During Seismic Interpretation and Reservoir Evaluation", The Integration of Geology, Geophysics, Petrophysics and Petroleum Engineering in Reservoir Delineation, Description and Management, Robert Sneider, Wulf Massell, Rob Mathis, Dennis Loren, Paul Wichmann
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This paper describes the methodology and application of a number of new structural-geo- logical techniques for analysing faults and fault systems. These are: firstly, fault-displacement analysis, which is used to establish the common fault-patterns for multiple horizons; secondly, analysis of horizon separations on correlated faults to evaluate reservoir connectivity; and thirdly, prediction of the fault-displacement population below the limit of seismic resolution. There exists a substantial methodology for achieving objectivity in the identification and mapping of geological horizons on seismic sections. By contrast, however, the mapping of faults and fault systems remains comparatively subjective with no firm methodology for deriving a 'correct' fault-map. Recent research has demonstrated that displacement varies systematically on fault surfaces and that by an analysis of displacement patterns on putative fault-correla- tions objectivity and methodology are introduced into fault correlation. We analyse displacement patterns on faults using interactive-graphics software. Once a consistent fault-pattern is established for all mapped horizons, reservoir connectivity throughout the area can be evaluated from horizon-separation diagrams which are produced automatically by our fault-analy- sis software for any selected fault. Further recent research has shown that prediction of the displacement population of faults and fractures below the limit of seismic resolution can be made from the seismically-resolved, fault-displacement population. Additional calibration of the fault-displacement population can be obtained from measurements made on cores from wells. The integration of these techniques enables a detailed analysis and description of faults and fault systems during seismic interpretation and reservoir evaluation.
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The Integration of Geology, Geophysics, Petrophysics and Petroleum Engineering in Reservoir Delineation, Description and Management
Bima Field, offshore northwest Java, is a sizeable reservoir containing reserves of approximately 700 MM bbls OOIP with a 50 BCF gas cap. At present only the northern 1/3 of the field is developed, with 7 platforms and 54 producing wells, of which 20 are horizontal. The field has multiple drive mechanisms and high viscosity oil (21 cp), resulting in rapid GOR and water-cut increase after 3 years of production. The high stakes (both reserves and facility investments) and the reservoir's complexities, make an effective reservoir management scheme critical. For this reason an integrated geological, geophysical and engineering description was carried out to provide a 3-D Reservoir Simulation Model to evaluate development options. Geologically, the Oligo-Miocene age Batu Raja Limestone was deposited on the Seribu Platform, a basement-controlled, fault- bounded structure. The Upper Batu Raja carbonate build-up is thickest on the structurally highest parts of the platform where the rock comprises a series of "cleaning upwards" cycles (muddy deposits overlain by progressively more grain-rich sediments). A Lower Miocene drop in sea-level caused subaerial exposure of much of the platform and leaching by meteoric fluids. This diagenetic event resulted in contrasts in the reservoir quality (porosity, permeability, fluid saturations) at various intervals of the Upper Batu Raja. Based on these dissimilarities, the reservoir was zoned into 6 model layers. Once zonation was established, well logs could be calibrated to whole and sidewall core. A dense grid of seismic data were used to map the Batu Raja structure. From these data, color seismic inversion sections were produced and calibrated to the well logs. The calibrated seismic data were then used to map the top of structure, the carbonate build-up's edges, the total thickness of the Upper Batu Raja (needed to control aquifer size in the model) and the thickness of the main pay zone (layers 1-3). Engineering reservoir description began with a detailed compilation of capillary pressure, relative permeability, production and DST data. The 3-D simulation model required special treatments, including varying the GOC depths to honor separate gas cap closures; making permeability pressure dependent in poorly-consolidated zones; and setting up horizontal well completion treatments. Results suggest that water injection into the oil rim and gas cap is an effective approach toward maximizing recoveries and minimizing gas cap resaturation. However, waterflood reserves are sensitive to injection timing. The synergistic approach of geological, engineering and geophysical input into the Bima reservoir study has had impact by delivering a reservoir management tool that can evaluate future development expansion and possible gas sales. The simulation model can also track fluid migration during the field's producing life. The geological/geophysical model led to an enhanced understanding of Batu Raja depositional and diagenetic processes that has potential in regional exploration strategies.