A computerized simulation model was constructed to synthesize the processes of petroleum generation, migration, and accumulation under relatively simple conditions. The model successfully simulated petroleum accumulation in an existing anticlinal gas field, and was used to estimate the possibility of fault and stratigraphic entrapment nearby.

A geologic cross section of the area is divided into a series of vertical columns that are sectioned into rectangular cells representing successive intervals of time and corresponding strata. Four geologic processes are sequentially performed on each cell or pair of adjacent cells. First, sediment is deposited in a cell with its original thickness restored by removing the effects of compaction (deposition). Then, for each time-stratigraphic unit, the compaction caused by increasing time and depth of burial is calculated; the system also estimates the amount of petroleum generated, assuming it to be a function of temperature (compaction and petroleum generation). Primary migration is assumed to occur when petroleum saturation of source beds exceeds the residual amount normally present n thermally mature shale. Secondary migration is assumed to result from buoyancy alone; any petroleum which exceeds the hydrostatic trapping capacity of the shale seal is either allowed to migrate into a cell located along some upward path or escape to the surface (petroleum migration).

The model was applied to the anticlinal East Niigata field, Japan, using carefully selected input parameters. Results made it possible to estimate migration paths and timing of entrapment in each producing zone. The model may also be applied to exploration problems. For example, it was used to estimate the possibility of petroleum entrapment in strata near the East Niigata field. Results of this experiment show that the simulation method is potentially useful for estimating the possibility and places of entrapment, especially for stratigraphic traps.

End_of_Article - Last_Page 964------------