Geochemical Significance of Seepage Oils and Bituminous Sandstones in the Albertine Graben, Uganda

Abstract

Geochemical analysis of surface samples comprising three seepage oils, two bituminous sandstones and five shales collected from the Ugandan portion of the Albertine graben (a Cenozoic rift basin in Eastern Africa) indicates that the basin may have some petroleum potential. The analyses show that seepage oils from the Kibiro and Paraa localities were derived from Types I or II1 source rocks, deposited in semi-deep or deep-water lacustrine environments containing abundant freshwater algae. However, the seepage oil from Kibuku is derived from a Type III source rock.

A comparison of the seepage oils and the bituminous sandstones suggests that there are at least two sets of mature or threshold-mature source rocks in the Albertine graben — one in the Upper Tertiary and the other in the underlying (pre-Upper Tertiary) succession. According to molecular indicators of maturity, the Kibiro seepage oil was generated during peak maturation, whereas the Paraa and Kibuku seepage oils are of lower or threshold maturity.

This work was completed under the supervision and guidance of Qingping Li, Chief Engineer of CNODC; Xiaoguang Tong, Chief Geologist of CNODC; and Reuben Kashambuzi, Commissioner, PEPD, MEMD, Uganda. The Embassy of the People's Republic of China in Uganda assisted with the completion of the project. Professors Tieguan Wang and Lihua Chen reviewed the research results, respectively. CNODC and the Ugandan authorities (PEPD) provided the favourable conditions for this project. Journal review was by Roger Swart (Namcor, Namibia) and Andrew Carr (Advanced Geochemical Systems Ltd) whose comments on the manuscript are acknowledged with thanks.