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Refined Lacustrine Petroleum Systems Modeling and New Play Assessment: A Case Study of Baxian Sag, Bohai Bay Basin


Baxian sag is mature exploration area about 2400Km2 with whole 3D seismic data, which located in the western area of Bohai Bay basin. 1.4 billion BBL oil has been found after thirty years exploration, and most of discovered oil accumulations were located the depth above 3500m. How to assess residual petroleum resources and to delineate next play are urgent issue for further exploration. Refined source kitchen analysis indicated that Paleogene Shahejie Formation lacustrine source rocks (Es1, Es3 and Es4) present highly heterogeneity, including organic facies C, D/E and F, and maturity range from oil windows to overmature stage in the deep area of sag. The scale and phase of residual petroleum resources can be inferred through the comparison of amount and phase between expelled hydrocarbon from source kitchen and discovered oil accumulations. Oil-source correlation confirmed that oil accumulations above 3500m depth were derived from organic facies C source rocks in the Shahejie Formation, most hydrocarbon expelled from organic facies D/E and F source rocks have not be found, we postulate that these condensate and wet gas expelled from the Es3 and Es4 D/E and F facie source rocks efficiently accumulate at the play and prospect in the deeper scope. The spatial orderly distribution of API GOR, gas carbon isotope and diamondoids data denote the various front expelled hydrocarbon in different mature stage from organic facies C, D/E and F, which reflect the dynamic scenario of petroleum migration and accumulation from kitchen to the shallow accumulations, therefore, the deep buried hills charged with condensate and wet gas were recommended the new play for further exploration, Recently, Niudong-1 Well have been successfully drilled and found a super-deep carbonate buried hill condensate gas reservoirs in the Mesoproterozoic Wumishan Formation, with the bottom depth about 6500m and GOR about 875m3/m3. The success of Niudong-1 Well has proven our model of the condensate and wet gas efficiently accumulates in the deeper prospect.