HYDROCARBON OCCURRENCE AND ACCUMULATION CONDITIONS FOR LITHOLOGICAL RESERVOIR OF PUWEI AREA DONGPU DEPRESSION CHINA

The lithological reservoir is well developed and has become one of the important exploration targets in Dongpu Depression recently. In this paper, rock-eval pyrolysis and gas chromatography-mass spectrometer (GC-MS) are used to analyse the hydrocarbon accumulation conditions of lithologic oil and gas reservoirs in the Puwei area, Dongpu Depression. The results show source rock is mainly developed in third and upper fourth member of Shahejie Formation (Es-3, Es-4(U)) with certain thickness and high abundant organic matter. The types of the source rock are mainly of type I-II1. Most of the source rocks are in the mature stage and have reached the peak of hydrocarbon generation, indicating well material foundation for hydrocarbon generation. Sand bodies are developed in Shahejie Formation with fine grains, multiple-thin layers, and fast-changed lithologies overlaid with low porous and permeable layers. Most of the deep reservoirs are already tight, belonging to low to medium porosity and low permeability reservoirs. Lithological traps are formed in an ancient small lacustrine basin with multi-sources and sedimentary systems. Therefore, the lithology of the sedimentary changes rapidly during the deposition. The well configuration of faults and sand bodies constitutes the main transport system (fault-sand composite transport system) for hydrocarbon accumulation in the Puwei area. Four sets of thick gypsum-salt rocks play an important role in controlling the concentration range and vertical enrichment of the hydrocarbon in the northern area of the Dongpu Depression. The results will shed light for the study of the accumulation mechanism of similar related lithological oil and gas reservoirs.