Shale Gas Accumulation Regularity And Favourable Areas For Ecast Of Wufeng-Longmaxi Formations In East ChongQing And West HuBei

The upper Ordovician Wufeng Formation and the lower Silurian Longmaxi Formation are the main formations of shale gas exploration in western Hubei and eastern Chongqing.Well Jiaoye 1 in the research area is one of the most successful shale gas wells in China,but other shale gas wells in the research area is less than perfect.In this study,we combine the basic geological data of the research area with field profile and drilling core observation,sampling and test analysis,to analyze shale sedimentary environment,facies distribution,burial depth,geochemical proxies,mineral composition,types and chatacteristics of micropores in the lower member of the Wufeng Formation,Guaninqiao Member of the Wufeng Formation,the lower member of the Longmarxi Formation,Besides,the shale tectonic evolution,history of the hydrocarbon and the water conditions of the strata have been studied.considering the evolution of shale and the preservation of the evaluation criteria,the favorable area of shale gas development is predicted,and the main results are:(1)The favorable material base of shale gas development is in the lower of Wufeng Foramation(Ordovician)–Longmaxi Formation(Lower Silurian)WF2-LM4 graptolite member The shale gas exploration of WF2-LM4 sedimentary center is better than that of shale gas under the influence of the uplifted and submerged area,where the WF2-LM4 member is thin and has a poor exploration effect.(2)Silicon content in WF2-LM4 graptolite member is high,which is more than 40%.While the silicon content of the LM5 graptolite gradually decreases upwards.The wf2-lm4 member is high in organic matter,where organic pore is also large and the pore structure is connected in three dimension,with low mineral porosity,and low fracture filled with organic matter.LM5 and layers above are low in organic carbon content and organic pores,but high in mineral pores and open fractures.(3)The upper Ordovician Wufeng Formation and the lower Silurian Longmaxi Formation,which were elevated during the Late Cretaceous Yanshan movement were characterized in late raising time,long hydrocarbon time,late hydrocarbon termination and well preservation of upper cover layer.While that elevated during the Late Jurassic to the Early Cretaceous were characterized in early rising,early hydrocarbon termination time and long duration in the overcoating damage.The area where rising time was in the Late Cretaceous and later,is favorable with well stratified water mineralization and geochemical proxies,is in well shale gas preservation condition.(4)Based on the selection evaluation method of the primary sedimentary conditions and the condition of later preservation of shale,the favorable area has been selected.It is believed that the Fuling area of eastern Chongqing and the area of the southeastern wuxi area in northeastern chongqing are the core regions of the shale gas reservoir development.