Abstract: The Analysis of Secondary Migration by Two-Dimensional Basin Model "SIGMA-2D"

Akihiko Okui, Mamoru Hara, Hideki Matsubayashi

Japan National Oil Corporation's SIGMA-2D is a two-dimensional two-phase fluid flow basin model, which can reproduce hydrocarbon generation, migration and accumulation. In SIGMA-2D, hydrocarbon generation is calculated by kinetic model with the temperature distribution through basin based on conduction and convection heat flow. Oil (or gas) and water migration, and sealing are simulated by Darcy's law with relative permeabilities and capillary pressure curves. SIGMA-2D can also evaluate tectonic fracturing/faulting in terms of fracture permeability derived by simplified stress-strain analysis.

In Niigata and Akita basin, which evolved as Tertiary back-arc rift basins in Japan, one of the main oil producing reservoirs is a turbidite sandstone in Pliocene. However, geochemical data and the result of oil-source correlation reveal that accumulating oils are sourced from overpressured shales in middle Miocene deposited under deep marine environment. Since these source rocks

around oil fields are generally immature, oils are supposed to migrate vertically and horizontally from deeply buried kitchen areas. Furthermore, the location and the relationship of these paths seem to be important, since oil accumulated horizon is limited even though several turbidite sandstone beds are identified in wells and on seismic sections.

The application of SIGMA-2D into these basins indicates that it has a capability to delineate effective migration paths. Oils have started its migration in Pleistocene, first migrated vertically through limited shear zone, then horizontally through a widely-distributed turbidite sandstone bed and reached traps recently. The constraint on simulations has been accomplished by the matching of calculated parameters with measured ones in wells.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994