Geology and Geochemistry of Oil and Gas

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PREFACE

The progress in the oil and gas industry is related closely to the acceleration of
discovery rates, exploration, development, and production of hydrocarbon resources. Exploration, development, and production of hydrocarbon resources must be based on reliable information, which helps to predict subsurface conditions and properties of oil- and gas-bearing formations. Main oil and gas reserves are found in sedimentary basins composed of terrigenous (siliciclastic), carbonate, and, sometimes, volcanic or volcaniclastic rocks. Preservation of high reservoir pressure and good properties of reservoir rocks and seals (caprocks) in these basins depends greatly on their origin and further evolution.
The process of sedimentation, and the following processes of diagenesis (i.e., physical, chemical and biochemical processes, which occur in the sediments after sedimentation and through lithification at near-surface temperature and pressure) and catagenesis (or epigenesis) (i.e., physical and chemical processes, which occur in the sedimentary rocks at high temperatures and pressures after lithification and up to metamorphism), cause alterations, which may enable one to predict oil and gas potential.


Considering an interest demonstrated by petroleum geologists and reservoir engineers, this book discusses the major theoretical and practical problems of petroleum geology and geochemistry as they are viewed at the end of the 20th century and the beginning of the 21st century. The treatment of the material is non-uniform in
the sense that the accepted scientific concepts are treated cursorily, just to maintain the completeness and continuity of the story, whereas the disputable and innovative issues are handled in more detail. The discussion is conducted from a position of the science of petroleum geology, geochemistry, and other related disciplines. For instance, in describing oil-bearing sequences, the main brunt is on depositional environments and such features as reservoir and fluid-sealing properties. A considerable attention is devoted to the transformations within the rockwater–organic matter system of the Earth’s crust with changes in the subsurface temperature and pressure. New reservoir and accumulation types are identified and their exploration/development features are defined. A variety of common reservoir engineering problems can be solved during field development and production by the integration of geological, geochemical, and engineering studies. For example, such studies can identify reservoir compartmentalization, allocate commingled production, identify completion problems (such as tubing leaks or poor casing cementing jobs), predict fluid properties (viscosity, density) prior to production tests, characterize induced fracture geometry, monitor the waterflood process and water encroachment, or explain the causes of produced sludge.

Discussions in this book are based on the systems approach to the specific geologic systems. Along with this approach, mathematical modeling of the static and dynamic geologic systems is described as well. The use of mathematical methods and computer techniques increases the scope of problems that can be solved on the basis of integrated geological, geophysical, geochemical and engineering information. Mathematical methods using computer processing of the current information accelerate the process of regional and local prediction of oil and gas potential that, in general, increases the economical and geologic efficiency of exploration, develop-
ment, and production of oil and gas.

George V. Chilingar, Leonid A. Buryakovsky

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