Distribution Of Mesozoic Fractural Sandstone Reservoirs In North Dongpu Depression

This thesis focuses on study of the fractures in the Mesozoic sandstone in Dongpu depression.Aimed to make clear of fractured reservoir distribution in the Mesozoic sandstone in Dongpu depression,a lot of work has been carried out on Mesozoic stratigraphic Chronology judgements,hydrocarbon-source correlation~-, fractured sandstone reservoirs forming,hydrocarbon accumulations controlling factors and distribution.The main conclusions drawn in this thesis are listed as follows.1.Confirming the Mesozoic stratum of Dongpu depression is middle-lower Triassic.Chronology of Mesozoic stratum of Dongpu depression has been unclear for a long time.In the Mesozoic of the Well Wei 77-3 and Wei 77-4,some middle-lower Triassic fossils were discovered in some cores,which is about 235Ma by isotopic age analysis.It provides evidence for cognizing Mesozoic stratum of Dongpu depression as middle-lower Triassic.Regional stratigraphic correlation in the Mesozoic between Dongpu depression and North China region is built up,which helps to realize the distribution of Mesozoic strata in Dongpu depression,which resolve the over 30-year disputations of stratum chronology in Dongpu depression.2.Mesozoic effective reservoir bed is fractured sandstone,which develop two-stage fractures controlled by tectonic stress.Mesozoic sandstone matrix in the north of Dongpu depression is not available for providing oil accumulating space. Sandstone fractures are well-developed,while mudstone fractures are not.Effective reservoir spaces are fractures and dissolved pore and cavities.Fractures in the Mesozoic sandstone reservoir were mainly formed by tectonic stress fields during Yanshan and Himalayas period.In the early stage,east-west trending fractures are formed mainly by horizontal extruding stress field,while North-east trending fractures are formed mainly by tectonic reverse which happened at the end of Dongying period. Tectonic stress is the extrinsic factor affecting sandstone fractures development. Lithology of the reservoir bed,thickness of sandstone and rock mechanics natures is the intrinsic factors for that.Fractures in the Upper Mesozoic strata and structural high are well developed through logging analysis and seismic interpretation.3.Petroleum in the Mesozoic derives from Neocene while natural gas from Carboniferous-Permian.According to hydrocarbon-source correlation,Mesozoic petroleum in the Well Ming 471 in Wenmingzai,Well Wei 77-3 and Wei 77-4 in Weicheng are from matured-low matured source rocks of interval ES3 and ES4. Mesozoic gas of Well Wei 79-9 in Hubuzhai is from underlying Carboniferous-Permian coal beds,supplying the Mesozoic reservoirs.4.Mesozoic reservoir is kind of laminated fractured burial hill reservoir. There is a new type of reservoir,called as laminated burial hill reservoir only with fractures as storage space,discovered in Bohai bay basin,characterized by oil only occurring in the fractures and dissolved pores and cavities,instead of occurring in the sandstone matrix.Hydrocarbon supplying condition determines the scale of the oil reservoir,lithology controls degree of fractures development,fractures controls hydrocarbon distribution and structure affects hydrocarbon accumulation.The time of Fracturing and its match with hydrocarbon generation and expulsion determines the effectiveness of hydrocarbon accumulation.3 types of hydrocarbon accumulations models are established for Tertiary fractured sandstone reservoir in Dongpu depression.The potential hydrocarbon resource is predicted as much as 3800×10~4t in this area and 3 favorable belts for exploration is proposed in this thesis.The research result of this thesis is used to assist in exploration decision-making,which brings great success in the oil and gas exploration in the Mesozoic burial hills in the north of Dongpu depression,which also can provide some clues for similar exploration work in other regions.