Research On Formation Conditions And Regionalization Of Tight Oil And Gas In Sichuan Basin

Sichuan Basin,located on the western margin of Yangtze plate,is a large superimposed basin rich in natural gas.In addition to conventional natural gas,Sichuan Basin is also rich in unconventional oil and gas,such as coal bed methane,shale gas,tight sandstone and tight carbonate oil and gas.The tight oil and gas is the focus of this study.On the basis of collecting data extensively and analyzing and summarizing results of previous research,we research the formation conditions of tight oil and gas,then forcast the favorable zones of Xujiahe formation(T3x)and Daanzhai segment(J1dn)and evaluate them comprehensively compartment.There are several sets of reservoir combinations of tight oil and gas in Sichuan Basin.We divided them into reservoir combinations of the Lower Paleozoic,the Lower Permian,the Upper Triassic of tight gas and tight oil reservoir combination of Jurassic roughly.There are three kinds of hydrocarbon accumulation mode,self-generating and self-storaging,new-generating and ancient-storaging,and ancient-generating and new-storaging,and each set of reservoir combinations is near the source or self-source of filling,reservoirs stacking or close to the sources.In the Upper Triassic(T3)reservoir combination of tight gas and the Lower Jurassic(J1)reservoir combination of tight oil,source rocks and reservoirs stacked to one another,like "thousand layers cake".This mode is easy to accumulate oil and gas directly into the reservoir after production,there conducive to the formation of tight oil and gas.Through the analysis of source rocks,we learned that source rock of T3 x is mudstone with coal,which generating coaliferous gas into the reservoirs.The source rock of J1 dn is dark mudstone,mainly generating oil into the upper and lower reservoirs.The most lithology of T3 x reservoir is lithic sandstone in Xinchang area,and porosity and permeability of this reservoir is poor as tight sandstone reservoir.The reservoir rock of J1 dn in the middle of Sichuan Basin is mainly shell limestone,which has very poor porosity and permeability,and the reservoir became tight carbonate reservoir by cracking.On the basis of studies on reservoir characteristics,we discuss the controlling factors of reservoir and relationship between source and reservoir,and select the favorable reservoir zones of T3 x and J1 dn in Sichuan Basin.Then we calculate the amount of geological resources of these favorable zones of J1 dn and select evaluating indicators to give a comprehensive evaluation and division,which is divided into priority exploration(development)area,secondary exploration(development)area and exploration(development)reserve area.Through comprehensive evaluation and regionalization,we learn that priority exploration area of T3 x is Block?in the middle of Sichuan Basin,and priority areas are Block ?and Block ? in the east of Sichuan Basin.The priority exploration area of J1 dn are Block ?and ? in the west of Sichuan Basin,and priority areas is Block ? in the west of Sichuan Basin.