Petroleum potential of Oligocene lacustrine mudstones and coals at Dong Ho, Vietnam - an outcrop analogue to terrestrial source rocks in the greater Song Hong Basin

The outcrop of Oligocene age at Dong Ho, northern Vietnam, may constitute a n immature analogue to offshore terrestrial source rocks in the greater Son g Hong Basin. The outcrop includes an interval with two source rocks: (1) h ighly oil-prone carbonaceous mudstones containing kerogen types IIA and IIA /I, and with TOC contents from 6.48 to 16.89 wt%, and HI values from 472 to 690; and (2) oil-prone humic coals (kerogen type III) with HI values from 200 to 242. The mudstones were deposited in oxygen-deficient lakes, which o n occasion were subject to marine influence, and the coals accumulated in f reshwater peat-forming mires. The coals have broad activation energy (E-a) distributions, while the mudstones have E-a distributions characterised by a pronounced principal E-a. During artificial maturation about 16-17% of th e organic carbon in the coals and 45-50% of the organic carbon in the mudst ones participated in petroleum formation. The two source rocks primary gene rate oil and secondary generate gas, however, the mudstones realised the ma jority of their potential over a more narrow temperature range than the coa ls. The excellent generative potential of the terrestrial source rocks at D ong Ho is encouraging for offshore exploration for reservoirs charged by Ce nozoic rift-lake successions. (C) 2001 Elsevier Science Ltd. All rights res erved.