Compaction of Argillaceous and Coarse-Grained Sediments

During the past quarter century, the exploitation of oil and gas reserves, associated with thick sequences of very fine-grained and coarse-grained rocks in Tertiary basins, have become increasingly important for fulfilling the world's energy needs. Many exploration and reservoir development problems have arisen which demand an analytical solution. The scientific problems have arisen which demand an analytical solution. The scientific and technological problems associated with these geologically young basin sediments include the origin, maintenance and distribution of abnormally high pore-fluid pressures, chemical changes induced in the interstitial water by compaction, origin and migration of hydrocarbons, temperature gradients, clay minerals phase changes and subsidence of the surface. Successful drilling to depths greater than 20,000 feet in these sediments and the amounts of the hydrocarbons discovered and produced depend to a great extent on our knowledge of the physical and mechanical properties and deformation characteristics of the sediments and the interrelationships between their various petrophysical and fluid properties. This paper is an historical review of studies dealing with the effects that gravitational compaction of sediments has on hydrocarbon reservoirs and source beds. Specific attention will be given to the generation of abnormal pore-fluid pressures, chemistry of interstitial fluids, compaction models, pressures, chemistry of interstitial fluids, compaction models, compressibility of the reservoir rocks and surface subsidence. Introduction It has been postulated that gravitational compaction of sediments is directly related to the following parameters and can be functionally represented in the following manner: C = (1) Where C is the degree of compaction, is the stress on the sediment system, is the velocity parameter for solids and interstitial fluids in the system, is the density, is the bulk volume of the sediments, is the porosity, is the permeability of the system, is the burial depth, t is the time, T is the geothermal temperature, and c represents the compressibility relationships. Gravitational compaction of sediments under the influence of their own weight has long been a recognized geologic phenomenon. In the seventeenth century Steno attributed variations in the attitude of sedimentary formations to compaction.