Enrichment Conditions And Recoverable Resources Of Shale Gas Of The Focus Layers In Southeast Chongqing

Southeastern Chongqing is the shale gas-bearing area being firstly studied and explorated in our country.The shale gas resource is abundant in this area.It has a theoretical value and practical significance to carry out further shale gas research in southeastern Chongqing.This area is located in the complex transition zone of the fold belt between the barrier and the trough,which has experienced multi-stage tectonic movement.Two sets of organic-rich shales are mainly developed in this area,i.e.Lower Cambrian Niutitang shale and Upper Ordovician-Lower Silurian Wufeng-Longmaxi shale,thus the basic geological conditions for shale gas enrichment in the study area are good.The dissertation summarizes the shale gas enrichment model,and systematically evaluates the shale gas recoverable resources in Southeast Chongqing by studying the favorable selection area and the evaluation method of recoverable resources based on the basic geological conditions.In the study area,the organic-rich shale gas of Niutitang and Wufeng-Longmaxi mainly distributed in the residual syncline.The shale gas enrichment model can be divided into syncline and fault model.The former is mainly developed in the large-scale NE-SW syncline,the organic rich shale is well preserved with moderate burial depth and large thickness of overlying stratum,which is conducive to shale gas enrichment.The center of depression is the best favorable area for shale gas enrichment.The latter can exist in syncline or slope belt structural units,and the existence of faults(especially thrust nappe faults)provides good sealing conditions for shale gas preservation.The activity of faults creates a space for shale gas accumulation,especially under the condition of large burial depth and good sealing of overlying strata.The shale in the study area is a typical marine sediment,and the degree of exploration and development is relatively low at present,thereby the superposition method of key parameters is used for shale gas favorable selection.Selecting key geological parameters with different weight coefficients to stack and developing favorable shale gas selection area can realize the optimization of favorable area simply,quickly and credibly and meet the needs of practical work.Four favorable shale gas areas in Southeast Chongqing are selected by this method,which are Youyang-Xiushan favorable area of Lower Cambrian,and Wulong-Lianhu,Pengshui-Qianjiang and Gongtan favorable area of Lower Silurian.The southeast area of Chongqing is enriched in shale gas resources.The geological resources,technical recoverable resources and economic recoverable resources of shale gas in the study area are calculated by probability volume method,analogy method and cash flow method respectively.They are 20944 million cubic meters,314.2 billion cubic meters and 26242 million cubic meters respectively.It is calculated that the technical recovery coefficient of Wufeng-Longmaxi Formation is 0.15 and the economic recovery coefficient is 0.10,which realizes the continuous evaluation of shale gas series resources from geological,technical recovery to economic recovery.The research results can be used as an important reference for further shale gas exploration and development in Southeast Chongqing,and provide theoretical basis for shale gas exploration and development in the middle and upper Yangtze area.