Multiple Stratigraphic Reservoirs Related With Weathered Granite Buried-Hill in Betara Uplift, South Sumatra Basin, Indonesia

Abstract

Betara uplift is located at the northern margin of South Sumatra back-arc rift basin in Indonesia, which is a secondary unit of Jambi depression. The area covers more than one thousand square kilometers. The basemant of Betara uplift is made up of granite, phyllite and metamorphic quartzite sandstone. About six oilfields have been discovered both Oligocene Lower Talang Akar Formation and the basal conglomerate of granite wash. These oilfields have been regarded as structural reservoirs. Almost all of the structural prospects have been drilled, it means more challenges to explore new oilfields. Based on the comprehensive study of geology, seismic and well logging interpretation, the geological model of Betara granite buried hill and alluvial fan skirt is established by identifying the paleolandform, alluvial fans and weathering crust, by delineating basement fracture system, meanwhile, by referring to modern granite weathering landform and valley-fan parallelism of alluvial fan deposition systems as analogues. Betara buried-hill experienced a long period of uplifting and weathering during Oligocene rift stage. The erosion landform of valleys, peaks, slopes was formed, while the basement was denuded, the weathered rind and the fractured granite zone remained on these paleohighs, and a near provenance fan skirt of more than ten wetland of alluvial fans was deposited on the front of valley mouths around the uplifts. In the weathered rind and fractured granite zone, three type reservoirs of pore, pore-fracture and fracture are effective reservoirs which were originated from the process of weathering and leaching. Three stratagraphic plays of weathered rind, fractured granite and alluvial fan are composed of multiple stratgraphic reservoirs. More than twenty prospects and leads of fractured, lithology and stratigraphic are delineated in Betara uplift. The results of this research provides three new zones and dozens of targets for discovering new oilfields in the Betara mature exploration area. The geological model is a good reference for petroleum exploration in South Sumatra basin, even if other similar rift basins in southeast Asia.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015