| A two-dimensional deductive forward model was set up to simulate fluid flow compaction and heat transfer through geologic time. In this model, two of the partial differential equations (time dependent and spatially two dimensional), Darcy's equation for fluid movement and the diffusion equation for heat transfer, are solved numerically. The model is tied to the modified Tissot's mathematical model for oil/gas generation and to a simplified material balance model for oil/gas migration where the separate hydrocarbon phase is assumed as the main mode of migration. The model yields pattern of the oil/gas migration through time, but also provides the user two dimensional views of geologic history including development of oil/gas generation and accumulation, as well as the fundamental parameters which include porosity, temperature, maturity, and pore pressure.; The model was tested with simple geological settings to see if it responded "reasonably" when compared with our general understanding of geology. The model was then applied to the Iwafune Oki area of Japan, and revealed that the main hydrocarbon generation occurred below the depth of 2500 meters for oil and below 3000-4000 meters for gas during the time from 2.0 MaBP through present. The possible reservoir in the area is favored by the "Green Tuff" which is the lowest member of the section and is covered by source rocks suggesting downward migration. Through the application, the model reveals that downward migration from the upper shale unit must have occurred almost constantly through the history of the reservoir, largely because capillary effects play such a significant role. Also, following a sensitivity analysis of the model, the effect of sandstone geometry on migration pathways is found to be very significant. |
