Multidisciplinary Reservoir Description, Walker Creek Field, Columbia and Lafayette Counties, Arkansas
D. M. Bliefnick, J. G. Kaldi, S. K. Bissmeyer, T. T. Dang, 1991. "Multidisciplinary Reservoir Description, Walker Creek Field, Columbia and Lafayette Counties, Arkansas", 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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An integrated reservoir description of the Smackover Formation in Walker Creek Field in southern Arkansas was conducted in order to evaluate the field's hydrocarbon potential and to determine the best method of increasing recovery. Geologic, petrophysical and engineering studies comprise the multi-disciplinary reservoir description of Walker Creek Field. Evaluating the field's potential included optimizing current operations, proposing options that accounted for reservoir complexities, and planning future operations that would maximize the unit's economic value. The specific aspects of the reservoir description consist of:
Determining the depositional and diagenetic controls on reservoir lithologies and the resulting reservoir geometry;
Establishing the internal geometry of the reservoir for the purpose of 1) zonation of reservoir flow units, 2) discrimination of pay from non-pay intervals and 3) evaluation of the continuity of different pay zones and of barriers to flow;
Relating facies to reservoir properties, including 1) petrographic evaluation of pore types, 2) relating depositional and diagenetic textures to capillary pressure (Pc) trends and 3) recognizing log responses associated with reservoir layers;
Providing a depositional and diagenetic model of the occurrence and distribution of reservoir and non-reservoir units in Walker Creek Field, which may have applications to exploration efforts elsewhere in the Smackover Formation.
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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.