GEOCHEMICAL SIGNIFICANCE OF SEEPAGE OILS AND BITUMINOUS SANDSTONES IN THE ALBERTINE GRABEN, UGANDA
Dou Lirong1,2,*, Cheng Dingsheng2, Wang Jianjun2, Ernest N.T.Rubondo3,
Robert Kasande3, Abdul Byakagaba3 and Frank Mugisha3
1Research Centre, China National Oil and Gas E & D Corp., CNPC, PO Box 910, Xueyuan Road 20, 100083, Beijing, P. R. China.
2Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, P. R. China.
3 Petroleum Exploration and Production Department (PEPD), PO Box 9, Entebbe, The Republic of Uganda.
*Author for correspondence, email: dlr@petrochina.com.cn
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 Mesozoic-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.