Reservoir Characterization: Petrophysical Formation Evaluation and Rock Description
Published:January 01, 1991
1991. "Reservoir Characterization: Petrophysical Formation Evaluation and Rock Description", 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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Petroleum exploration and development programs can benefit significantly through the integration of petrophysical analysis. Quantitative assessments of hydrocarbon volumes and anticipated production characteristics can improve the exploration and development decision process and reduce risk. Canadian Hunter's success at applying this philosophy reflects three key ingredients: people, technology and a work environment which fosters innovation.
Petrography is fundamental to all aspects of successful formation evaluation. Rock framework components and secondary constituents are characterized for their impact on log response. The descriptions of pore types and volumes guide the selection of critical parameters affecting fluid flow and electrical properties.
Log analysis techniques begin with a model which incorporates the petrographic data. Improvements in data resolution yield better quantitative models to describe the pore space available for hydrocarbon saturation. Permeability measurements calibrated to in- situ reservoir conditions provide the basis for productivity estimates.
Drill stem tests and production tests are used to calibrate the well log calculations of porosity, water saturation and producibility. Comparisons to known results provide a reference for the well or formation being considered.
Technology transfer is enhanced through specialists working on exploration problems through to the development phase and back into exploration. The pragmatic application of “state of the art” technology must be practised routinely for this approach to be successful. A receptive environment reaching through to the top levels of management is an underestimated requirement in achieving results through petrophysical integration.
It is an honor to be part of this tribute to recognize the contributions of Gus Archie
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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.