Modeling petroleum generation in the Southern Muglad rift basin, Sudan

Maturity and petroleum generation have been modeled in a 120-km-long northe ast-southwest cross section of the Southern Muglad basin, Sudan. The sectio n passes close to the Unity and Kaikang areas, which provide well control o n the structure interpreted from gravity and seismic reflection profiles. M odeling of geotherms from corrected bottom-hole temperatures indicates pres ent heat flows around 60 mW/m(2) in the well control areas. Using measured vitrinite data as calibrant, maturity can be modeled equally well with a co nstant paleoheat flow similar to the present day or with a complex heat flo w; pattern related to rifting, A geologically realistic complex heat flow m odel was employed to calculate the timing of generation and expulsion from the Lower Cretaceous lacustrine source rocks of the Abu Gabra and Sharaf fo rmations. Kinetic (Easy% R-o) calculation of vitrinite maturity indicates a projected oil preservation depth limit around 4000 m shallowing to around 3500 m northeast of Unity near the basin margin. Modeling of hydrocarbon evolution in the main hydrocarbon kitchen areas ind icates an early phase of Oil expulsion from lower source units between 110 and 95 Ma prior to Upper Cretaceous reservoir deposition. Oil in Darfur Gro up reservoirs of the Unity field probably was sourced initially from the up per Abu Gabra in the main kitchen area between 80 and 60 Ma and may have re migrated from deeper reservoirs during Tertiary rifting, Subsequent oil cha rge probably migrated from the lower Abu Gabra in minor kitchens northeast of the Unity-Heglig ridge, which may have expelled oil until Miocene uplift , The petroleum system probably is relatively inactive at present. Volumetr ic calculations for the Sharaf and Abu Gabra source formations suggest that around 10(12) bbl of oil and 10(14) m(3) of gas have potentially charged r eservoirs, although much may have been expelled prior to trap development. Apparent lack of significant gas accumulations may reflect leakiness of tra ps during rift-related fault rejuvenation.