| The area of Shunbei is located in the Midwest of the Tarim Basin.It is located in Awati and Sha Ya county,the Xinjiang Uygur Autonomous Region.The tectonic position is in the transitional part of the Awati fault depression,the Sha Ya uplift and the Lower Uplift of the Shuntuoguole.The regional reservoir forming conditions and recent exploration results prove that the Ordovician strata in the area of Shunbei is one of the most important target blocks and target layers for oil and gas exploration in Tarim Basin.Therefore,this paper,based on the principle of petroleum geology and the collection of geological data,seismic data and so on,combining the characteristics of formation and tectonic evolution.Then expound and analyse the oil and gas accumulation characteristics of the Ordovician system in the area of Shunbei.The distribution of present-day faults in Tarim Basin is the result of multi period tectonic movement.According to the sequence of fault formation and the extension direction,the structure of the Tarim Basin is controlled by the NWW direction,the NEE direction,the EW direction and the NNE direction to be the rhombic block.The main tectonic activities which control the formation and evolution of fault structures in Tarim Basin are Caledonian,Hercynian,Indosinian Yanshan and Himalayan epoch.Three main fault zones are developed in the 1 well area in the area of Shunbei,the main distribution direction is the NE direction and the NNE direction,and the active period is the early Caledonian-Hercynian-Himalaya period.The oil and gas accumulation conditions in the Shunbei area are good.First,the Ordovician crude oil of the Shunbei area has similar geochemical characteristics with the crude oil of Yuejin,Tahe and the deep of Tahe,mainly from the source rocks of the Cambrian Yuertusi formation.According to the reservoir space combination and its distribution features,togathering the reservoir lithology,sedimentary facies and sequence characteristics,divide the reservoir of Ordovician carbonate rocks into three types,namely,the limestone fracture-hole type reservoir,the dolomite vuggy type reservoir and the fault-karst reservoir.And the dissolving body reservoir is the most important.According to the drilling data,the mixed continental shelf mudstone developed in the upper Ordovician Qiaerbake-Lianglitage-Sangtamu formation,which is the most stable regional cap rock in this area.The Ordovician oil and gas trap in Shunbei area is mainly the fault-karst trap.It is speculated that there still exist 2 kinds of stratigraphic traps,namely,carbonate limestone cave fractured reservoir and dolomite vuggy reservoir.The strike slip faults and fracture systems which connect the Cambrian Yuertusi formation hydrocarbon source rocks and the Ordovician carbonate reservoirs are the most critical vertical transport system in the Ordovician carbonate reservoirs in the area of Shunbei.The karst cave type limestone reservoir and dolomite vuggy type reservoir under the three order sequence interface,T78?T76?T75?T74,are the horizontal transportation system of the carbonate reservoir of the middle-lower Ordovician in Shunbei area.Through the anatomy of the oil and gas reservoirs in the No.1 fault zone,the main control factors of the Ordovician carbonate reservoir formation in the Shunbei area can be summarized as“interface controls the reservoir,fracture controls the reservoir and the hydrocarbon accumulation”.The Ordovician carbonate rocks in the Shunbei area developed high stage(four order sequence interface)karst,low stage(three order sequence interface)karst and weathered crust(two order sequence interface)karst in sequence.Each sequence interface have obvious control effect on limestone cave fractured type reservoir and dolomite vuggy type reservoir.They also have a certain control effect on the reservoir of fault-karst.Last,summarize the oil and gas enrichment regularity of the Ordovician system in the Shunbei area and distinctive features of the oil and gas accumulation have been found. |
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