Oil-source correlation in the Fulin basin, Shengli petroleum province, East China

The Fulin basin is located within the giant Shengli petroleum province in East China. The source rock in the basin is mainly the lower part of the Third Member (Es3) of the Eocene portion of the Shahejie Formation. It is composed of organic-rich dark mudstone and oil shale of lacustrine origin and contains good quality Type I-II kerogen. These strata reach the oil-generative stage at R(0) = 0.4-0.8%. The First Member (Esl) of the Oligocene portion of the Shahejie Formation has excellent oil potential in the nearby Gunan basin but is immature in the Fulin basin and is not an effective source rock. The oil and rock samples from both basins can be grouped into three major families based on biomarkers. The first family shows low Pr/Ph (<1), a high gammacerane index (>0.3) and notable beta-carotane, typical of carbonate-evaporite environments. This family exists in Esl rocks and the related oils and is early mature [beta beta/(beta beta + alpha alpha) = 0.2 - 0.3, and S/(R + S) = 0.10 - 0.20]. The second family shows high Pr/Ph (>1), a low gammacerane index (<0.2) and abundant 4-methyl steranes, indicative of freshwater lacustrine conditions like those in Es3. This family shows higher maturation [beta beta/(beta beta + alpha alpha) = 0.30 - 0.50 and S/(R + S) = 0.35 - 0.55] and notable diasteranes. The third family is transitional, has source and maturity ratios between the above families, and occurs in the Es3 unit samples from the basin interior. Based on biomarker similarities between oils and rock extracts, all oils in the Fulin basin originated from Es3 source rocks. Slight maturation differences indicate that these oils have been derived from different source areas. No oil from Es1 is found in the Fulin basin, suggesting Es1 source rocks are too immature to generate commercial oil. Although the nearby Gunan basin has much oil generated from Esl source rocks, no migrated oil from Es1 in this basin reached the Kenli faulted zone because of intervening faults which disrupt migration. Copyright (C) 1996 Elsevier Science Ltd