The paleotopography restoration and lithologic traps identification in faulted depression basin based on accommodation space and sediments supply: A Case on Abu Gabra formation in block 1/2/3 of Sudan, Muglad basin

Abstract

Finding oil and gas in lithologic traps is still a big challenge in faulted basin, with multi-periods tectonic subsidence, complicated fault systems and provenance supply variations, and paleotopography restoration is the necessary and essential step to study sediments characteristics and reservoir sands distribution, especially with thin sand and shale interlayers. Taking AG formation of block 1/2/4 in Muglad basin as an example, based on accommodation space and sediments supply (A/S) view, paleotopography restoration in each member of faulting AG formation has been done with seismic-well tie data. Deposition happens when base level is higher than ground surface, erosion happens when base level is lower than ground surface, and deposits bypass when base level is near ground surface. Moreover, compared with other traditional methods, such as sand porosity or shale acoustic time difference simulation, geothermal gradient or vitrinite reflectance regression, the method has advantages on free of samples limitation or basinal scale large area application, with 85% coincidence rate of 89 wells. With hydrodynamic analysis of sedimentary facies classification, fan delta, braided delta, delta front and turbidite sands were identified. Based on paleotopography restoration results, source rock evaluation (TOC, HI, Ro and Tmax), reservoir sands evaluation (favorable sands distribution and porosity) and cap rock evaluation (shale thickness) of Neem- Azraq area, northeast development zones in block1/2/4 were done. (1) Source rock in AG2 and AG3 members were favorable in AG formation of high TOC and mature, most in oil generation phrase with II1-II2 type. (2) subaqueous distributary channels and turbidite sands were favorable for lithology traps of relatively high sand/bed ratio, slope belt in paleotopography restoration, with 10-40% neutron porosity. (3) 100- 400m gross shale thickness from AG4 to AG2 member were favorable cap rock. Compared with multiple seismic attributes, RMS can be an effective way to indicate sands distribution and finally 10 lithologic traps of AG formation were identified with near three billion tons of oil-gas resource increase.

AAPG Datapages/Search and Discovery Article #90343 ©2019 AAPG Southwest Section Annual Convention, Dallas, Texas, April 6-9, 2019