Geologists have an important role to play in the management of oil and gas reservoirs and, especially, in the implementation of enhanced oil recovery (E.O.R.) projects. Cooperative work by engineers and geologists is needed to maximize the ultimate recovery of producing fields, because many of the problems that arise in their development are related to reservoir heterogeneity, mineralogy, or petrophysics Geologists should be involved in all aspects of an E.O.R. project, from selection of an appropriate process for a particular reservoir, through reservoir description and simulation of performance, to avoidance or solution of problems during the installation, operation, and evaluation of the project.
Among the larger scaled geological factors that affect reservoir performance are the distribution and attitude of the reservoir rocks and enclosing less permeable strata, the arrangement of facies within the reservoir interval, its layering or stratification, presence of shale “breaks” within the reservoir interval, natural fractures, and the influence of a hydrodynamic pressure gradient on the movement of fluids within the reservoir. Smaller scaled features also are of great importance. These include the texture and mineralogy of the reservoir rock, the types and arrangement of clays, and the geometry of the pore system.
Perhaps the most unique contribution a geologist can make to understanding the production performance of a reservoir or of individual injection or production wells in an E.O.R. project is his ability to recognize and predict the distribution of different “rock types” through the application of conceptual models of facies distribution and an understanding of diagenetic modification of those patterns of rock facies.
Figures & Tables
This volume is a collection of papers which focus on the sedimentology of siliciclastic sandstone and carbonate reservoirs. The papers were selected to show how detailed sedimentologic descriptions, when combined with engineering or other subsurface geologic techniques, yield reservoir models which may be used for reservoir management during field development and during secondary or tertiary enhanced oil recovery. In all the papers the framework for the field descriptions relies heavily of full-diameter cores. In addition to conventional 4-inch-diameter cores, frozen and rubber-sleeve cores were utilized in one or more of the studies. In addition to cores, at least one other geologic or engineering technique is integrated into each study. This integration of sedimentologic descriptions with other techniques gives rise to synergism.