Tectonic Evolution and Its Influence on Hydrocarbon Accumulation of the Ruman Buried Hill in Melut Basin, South Sudan

Abstract

Melut Basin is a Meso-Cenozoic intracontinental rift basin in Central African Shear Zone. It has experienced three phases of rifting-sagging cycle. However, the Ruman buried hill in this basin found multiple unconformities in seismic profile, which proves that it suffered multi-period uplifting and denudation, leading to complex hydrocarbon accumulation in Ruman area. Therefore, studying the relationship between tectonic evolution of Ruman buried hill and hydrocarbon accumulation can effectively guide petroleum exploration in this area. Based on the tectonic stress analysis and the recovery of denudation thickness by trend-thickness method of well-seismic stratum, the tectonic evolution of Ruman buried hill was restored by using balance profile analysis. And combined with the hydrocarbon generation and expulsion history in Ruman depression, the time matching relationship between hydrocarbon accumulation elements was analyzed and favorable traps are pointed out. The results show that the Ruman buried hill suffered two periods of tilting and uplifting. In the late Cretaceous, it suffered the second period of tilting and uplifting, the amount of depression stretch was 4.2%, the sedimentation rate was 93m/Ma, and the buried hill exposed area was 10km2. A series of overlying traps of Cretaceous formed around the buried hill. In the late Paleogene, the exposed area of buried hill reached 50km2, weathering denudation led to the development of basement fracture. Also, the source rock entered the stage of large-scale hydrocarbon expulsion during regional caprock deposition in the mid-Paleogene, Also, the hydrocarbon has been accumulated after the regional caprock deposition in the Paleogene, Cretaceous structures and stratigraphy-lithologic traps. However, the tilting and uplifting of the Late Paleogene resulted in the erosion of a large area of buried hill, Paleogene and Cretaceous structural reservoirs have been destroyed and only heavy oil reservoirs remained, while the lithologic reservoirs in slope close to depocenter are less damaged and well preserved. Therefore, the influence of tectonic evolution on hydrocarbon accumulation in Ruman area is mainly concentrated in the late Cretaceous controlled traps and the Late Paleogene controlled reservoirs while locally destructed. And so, the favorable traps and reservoir types in the Ruman area are stratigraphic-lithologic reservoirs with well preserved in slope close to depocenter and basement fracture reservoirs.

AAPG Datapages/Search and Discovery Article #90332 © 2018 AAPG International Conference and Exhibition, Cape Town, South Africa, November 4-11, 2018