Jianghan Plain Area, The Paleozoic Marine Source Rocks In The Secondary Hydrocarbon Generation Of Research

It is very important to search for advantageous area and targets of oil and gas exploration from marine formation in Jianghan plain by evaluating hydrocarbon-generating effect of Mesozoic-Paleozoic source rocks during geologic time, especially secondary hydrocarbon-generating potential and the condition of late reservoir forming.The abundance, type, maturity and the geochemical characteristics of the organic matter or its dissolved component of six sets of the source rocks in this area are appraised integratively in this paper. The results indicate that the four sets of main source rocks including upper Sinian, lower Cambrian, lower Silurian and Permian in this area are crucial to form reservoirs.The erosional statum thickness is resumed by applying the model system of thermal history and tectonic-thermal evolvement. The remnant thickness is gained by inverting erosional quantity and explaining seismic data. The results uncover the evolving courses of burial history of the source rocks in this area. There existed four burial-history types including continuous deep burial, deep burial-erosion-level, deep burial-rise-deep burial and deep burial-rise-shallow burial. It is of significance for the source rocks undergoing continuous deep burial and deep burial-erosion-deep burial to generate hydrocarbon late. The study on the maturity change of the organic matter validates secondary hydrocarbon generating, but different sections or beds of the same section have some disparity.The model results of hydrocarbon-generating history for the source rocks show further good prospect. The upper Paleozoic source rocks are of relatively high hydrocarbon-generating intensity during early Yanshan stage and lightly higher secondary hydrocarbon-generating potential during late Yanshan and Himalayan stages in Dangyang synclinorium comparing to in Chenhu-Tuditang synclinorium. They are considered to be able to form large and moderate fields. The lower Paleozoic source rocks generally have potential to form moderate and small fields except for Dangyang synclinorium from Caledonian to early Yanshan stage. They are of high intensity of the secondary hydrocarbon generating in Chenhu-Tuditang synclinorium area during late Yanshan and Himalayan stage, which have potential to form large reservoirs.In the light of the study on the reservoir-forming by secondary hydrocarbon-generating, it is considered that the key to the late reservoir-forming is around the hydrocarbon-generating center, excellent combination of tectonic evolvement and hydrocarbon-generating history, well trap types which have routeways to the source rocks, good direct cover and reservoirs.It is thought that southern Chenhu-Tuditang synclinorium is the promising area for finding oil and gas because of neighboring hydrocarbon- generating center, high intensity of secondary hydrocarbon-generating, well transporting system, good Cretaceous reservoirs and excellent preservative character of Cretaceous and Tertiary regional cover.