MELLO, ULISSES T., Lamont-Doherty Geological Observatory of Columbia University, Palisades, NY, and GARRY D. KARNER, Columbia University, New York, NY
One of the most dramatic geological events in the development of the Gulf of Mexico basin has been the rapid, late-stage deposition of Tertiary and Quaternary sediments of the Mississippi delta system. Significant geopressures have been created (and dissipated) at various times within the Gulf and track, in general, the west to east migration of sediment loads deposited since the Cretaceous. In some cases, sedimentation rates were extreme and therefore conducive to overpressuring. Consequently, these sections had anomalously low thermal conductivities and as such would have acted as thermal insulators to the conductive flow of heat. We have modeled the generation and destruction of abnormal sediment pore pressures owing to variations in sedimentation rate, facies type, and formation p rosity and permeability using finite-element analysis to solve the coupled differential equations of both heat and fluid transport in a "fully compacted" sediment matrix system. We assume initially that the porosity-effective stress relationship within the sediment follows a negative exponential steady-state form. An important implication of this modeling approach is the ability to forecast the anomalous development of sediment temperature as a function of depth and time. With this defined, we then model the thermal maturation of various age source rocks within the Gulf of Mexico using chemical reaction kinetics to predict the conversion of kerogen to oil and gas, oil to gas, and kerogen to the degree of vitrinite reflectance. We constrain the regional maturation behavior of the Gulf by atching the predicted with the observed distribution of vitrinite reflectance. We find the the history of sediment overpressuring is important for the timing of both source maturation and hydrocarbon expulsion.
AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)