Analysis Of Reservoir Forming Conditions And Exploration Potential In North Belt Of Chezhen Sag

North belt of Chezhen sag located in northern of Chezhen sag and the hanging wall of Chengzikou swell. Multiple series of strata and types sandstone-conglomerate body developed around the swell. They were the main petroleum migration direction and have superior exploration potential. But their complicated forming and distribution conditions brought difficulties for exploration, which were mainly put up as follows:fault belts with different strike usually have superior difference in active period and fault property and caused great influence to types and distribution of sandstone-conglomerate body; for very thick and lack of stable distributional mud interlayer, stratigraphic correlation of sandstone-conglomerate body is hard; types of sandstone-conglomerate body are diversiform and their spacial distribution character are complicated; forming reason and distribution character of effective reservoir are still unclear; multiple petroleum reservoir types and oil-bearing strata caused complicated petroleum enrichment regular pattern; there is short of effective exploration technology series for sandstone-conglomerate body petroleum reservoirs. Therefore, by research for sandstone-conglomerate body’s strata, structure, deposition and reservoir characters, new methods suitable for strata partition and correlation and effective reservoir recognition and evaluation of continuous type steep slope sandstone-conglomerate body can be concluded and perfected and will direct petroleum exploration in north belt of Chezhen sag effectively.Through Integrated application of geophysical, drilling, logging, and stratigraphic and geochemical analysis, multiple sequence surfaces of sandstone-conglomerate body in north belt of Chezhen sag were recognized and strata correlation framework was built. Sandstone-conglomerate body’s depositional system types were concluded and its spacial distribution character was made clear. Depositional models of reservoir were built and used to forecast distribution of profitable reservoir. By dissection of petroleum reservoir and analysis of sandstone-conglomerate body petroleum reservoir forming regular pattern, petroleum reservoir forming model was constructed. Based on researches above, objects were evaluated and profitable objects were chosen for exploration.Several achievements and conclusions acquired after these researches: (1) Sag border faults’ developments’ influence to sandstone-conglomerate body’s type and spacial distribution was analyzed. Different strike faults consisted north belt of Chezhen sag and every fault caused different depositional types for individual active period and property. These depositional types combined with those developed in the hanging wall of border fault constituted multiple depositional configurations and there are superior difference in deposition and reservoir character of these configurations.(2) Forming mechanic of sublacustrine fan in north belt of Chezhen sag was made clear. Large-scale sublacustrine fans developed in north belt of Chezhen sag and can be classified into two types:slump type and channel type. Slump type sublacustrine fan formed by front of nearshore subaqueous fan sliding into deeper water because of environmental destabilization and has the character of aggradation. Channel type sublacustrine fan formed by fragment’s direct deposition into deep water along certain source channel and is closely related to depositional center’s transfer.(3) Factors controlling reservoir physical property of deep-buried fans were found out. Deep-buried (buried depth bigger than4000m) fans in north belt of Chezhen sag usually have poorer reservoir physical property and are strong heterogeneous. But for the reason that fans’ parent rocks are carbonate of the lower Paleozoic and can act as source rocks, organic acid accompanied by hydrocarbon forming would corrode fans strongly. Abnormal pressure fluid compartments enhanced corrosion and was some help for fractures’ forming.