The Benefits of a Synergistic Approach to Reservoir Characterization and Proration Rose City Prairie Du Chien Gas Field, Ogemaw County, Michigan
Published:January 01, 1991
C. N. Tinker, L. D. Chambers, H. J. Ritch, C. D. McRae, M. A. Keen, 1991. "The Benefits of a Synergistic Approach to Reservoir Characterization and Proration Rose City Prairie Du Chien Gas Field, Ogemaw County, Michigan", 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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Gus Archie stated, in the AAPG Bulletin during 1950, “Petrophysics pertains to the physics of particular rock systems whereas geophysics pertains to the physics of larger rock systems. It is the study of the physical properties of rock which are related to the pore and fluid distributions. These properties pertain to the detection and evaluation of hydrocarbon bearing layers.”
Twelve years later, during an in-house conference at Shell, Bob Sneider said “The depositional environment is the important clue to the distribution and continuity of porosity, permeability, and barriers to fluid flow … even though the sand is altered by diagenesis.”
During 1977 the Senior Technical Editor of the JPT. Joe Richardson, said “Great strides have been made in studies of how the environment of deposition can effect rock character. Conceptual models based on these studies combined with geophysical as well as engineering data from well tests, cores and logs provide the basis for a modern approach to reservoir description.”
As a result of these seminal thoughts, the value of integrating disciplines that focus on the subsurface, namely” geophysics, petrophysics, geology and reservoir engineering, has become more and more apparent over three decades.
Synergy is defined in Webster as “The cooperative actions of discrete agencies so that the total effect is greater than the sum of the effects taken independently.” How does one integrate independent disciplines into a synergistic team?
Max DePree, in Leadership Is An Art provides a clue: “The first responsibility of a leader is to define reality. The
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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.