The Research On Shale Gas Enrichment Pattern And The Favorable Area Optimizing Of Wufeng-longmaxi Shale In Middle And Upper Yangtze Region

Based on a large number of experimental,sedimentary and Stratigraphic data of outcrops,wells of Wufeng-Longmaxi shale in the Upper and Middle Yangtze regions,the deposition and reservoir characteristics of the orgianic rich shale are systematically analyzed.The main controlling factors of organic-rich shale deposits and the controlling factors of the pore development of shales have been identified.The features of shale gas reservoirs in Weiyuan,Changning and Wuxi areas have been System analysed.The “dessert area” evaluation system of shale gas in southern China have been established and the shale gas production area are prefered.A systematic study of the biostratigraphic division of graptolite was carried out for key marine sections and well drilling in middle-upper yangtza area.South of Sichuan,northeast of Sichuan and Guizhou-chongqing were the key areas for study,and the differences in the sedimentation time of organic-rich shales in three different regions were clarified.The organic-rich shale in Weiyuan was mainly deposited in LM1-LM8;and the organic-rich shale of Changning is mainly deposited in the WF2-LM4 and the organic-rich shale deposition center gradually moves northwards over time.The organic-rich shale in the Guizhou and Chongqing area is mainly deposited in the WF1-LM4 stage and the organ-rich shale is mainly distributed in the Jiaojia 1 well and its surrounding area.The organic-rich shale distribution of Guizhou and Chongqing has the same evolution characteristics of weiyuan-changning,and the closer it is to the south,the earlier the deposition of organic-rich shale ends.The northeastern part of Sichuan basin exhibits an overall upward trend,with Wuxi as the depositional center of wufeng-longmaxi shale in the area.The shale deposition time of organic matter is from WF2 to LM9 and the thickness of organic rich shale is large.In general,there are two thickness centers in the organic-rich shale deposits in Sichuan Basin.The closer to the northern part of the basin,the higher the siliceous content of organic-rich shales has.The areas with a large thickness of organic-rich shale are mainly distributed in Fushun-Yongchuan and Wulong-Shizhu area in the east of Sichuan.The paper system summarizes the characteristics of the pores in the shales of Wufeng-Longmaxi shale in the Upper and Middle Yangtze regions.The system summarizes the mesopores of shales in the Wufeng-Longmaxi Formation in the Upper Yangtze and Middle Yangtze regions.The shale pores are divided into organic pores,inter-clay mineral pores,strawberry-like pyrite intercrystalline pores,and dissolved pores.Among them,the organic pores are Storage space and organic matter content is one of the main controlling factors for the development of shale porosity.By comparing the shale development characteristics of different strata(the Wufeng-Longmaxi and Qiongzhusi)and shale in different tectonic regions,it is believed that(1)the larger the pore size of the organic pores in the shale,the higher the organic matter content,and the worse for the pore preservation.(2)The larger the deepest ancient burial depth of shale,the earlier the time when the hydrocarbon generation capacity begins to decline,the worse for the pore preservation.(3)The more complicated the regional structural conditions and the worse the preservation conditions,and the worse for the pore preservation.The pore development model in organic matter of the shale was established and the development stages of organic matter pores were divided into 3 stages.They were:(1)the organic pore development stage,(2)the organic pore destruction stage and(3)the organic pore destruction stage.It is concluded that the favorable areas for the development of pores are mainly concentrated in areas where the maximum depth of ancient burial is relatively small,where the structure is relatively stable,and where the pressure coefficient is high.The characteristics of shale such as structure,sedimentation,rock minerals,geochemistry,physical properties,and gas-bearing have been systematically dissected in the Weiyuan,Changning and Wuxi shale gas fields and it discovered the main controlling factors for shale gas enrichment in different regions are different.The enrichment condition of shale gas which has relatively stable thickness distribution,good preservation conditions is good.The existence of the ancient uplift in the Weiyuan area affected the geochemical indicators of shale and reservoirs.The basic parameters and recent exploration results show that the prodution in the depressed areas far away from the ancient uplift is relatively high,indicating that the distribution of high-quality reservoirs is the key to the high yield of shale gas in weiyuan area.The main controlling factors of shale gas enrichment in the Changning area are structural preservation conditions.The farther away from the erosion area,the more shale gas is enriched in Changning shale gas field.Although the thickness of shale in Wuxi area is relatively large,the intra-regional tectonic movement is strong,the preservation conditions are relatively poor,the overall porosity is low,and the pressure coefficient is also low,which is not conducive for the ultimate accumulation of shale gas.Based on shale gas deposition conditions,reservoir development conditions,shale gas conservation conditions,combined with shale gas engineering conditions and economic conditions,we established a parametric system for optimizing and predicting dessert zones with target layer,condition layer,and parameter layer.The dessert area optimization and forecasting parameter system was evaluated and weighted on the geological parameters,compressibility and economic indicators of shale,and seven shale gas projects such as Shizhu-Fuling,Fushun-Yongchuan,Changning and Weiyuan were selected.The favorable areas for production and the replacement blocks have been ranked,and the exploration and development of shale gas should be carried out in the order of scoring.The favorable area for this paper is the main direction of shale gas exploration and development in China in the next few years.