Accumulation Conditions And Resource Potential Assessment For Shale Gas In Northwest Hunan

Shale gas is a hot spot in China's petroleum industry.Shale gas resources prospect was estimated to be good,however,systematic works on shale gas accumulation geological conditions has not studied yet in this area.In this paper,accumulation conditions,favorable areas and resource potential assessment on shale gas were studied.(1)Two organic-rich shales in Palaeozoic were developed in Hunan Province,with the characteristics of high thermal maturity,high fragile mineral contents,low clay minerals contents,low porosity and permeability,well-developed micro-pores.The Niutitang shale was deposited in deep shelf or deep sea,with the characteristics of high thickness,great buried depth,high organic richness,which make it the excellent conditions for shale gas accumulation.While the Longmaxi shale was developed on the edge of deep shelf,with characteristics of low thickness,shallow buried depth,lower organic richness.Based on studies on shale gas accumulation conditions,the shale gas accumulation modes of Niutitang Formation in continental slope-continental shelf and Longmaxi Formation in the closed bay edge were built.(2)Gas content in Well Changye 1 targeting to Niutitang shale in is good,and its most favorable depth for shale gas accumulation was 1100-1250m.While gas contents in Well Yongye 1 targeting to Longmaxi shale is relatively low,which have favorable conditions in 526.83-533.43m.The organic carbon content,specific surface area,total pore volume,pyrite,quartz,clay are the main factors that had influences on shale gas contents.Analysis on N2 in shale showed that the atmosphere was the main sources of N2 in the reservoir,indicating the poor storage conditions of Well Changye 1.High content of N2 in shales is universal in Northwest Hunan Province.(3)Base on organic carbon content,thermal maturity,thickness and depth,the favorable areas of shale gas distribution were selected with superimposed method.The favorable areas were Changde-Taoyuan-Cili-Shimen,Southeastern Longshan,Yongshun-Baojing-Huanyuan and Northwestern Shimen for Niutitang shale gas exploration and Yongshun-baojing-huayuan for Longmaxi shale gas exploration.By fitting the data on isothermal adsorption tests and field desorption tests,shale gas contents were calculated,which verified the reliability of favorable areas for shale gas exploration.The shale gas resource potential in Northwest Hunan Province was evaluated by probability volume method,with geological resources of 3.12×1012m3.The papers focused on the shale gas accumulation conditions and resources potential assessment of Northwest Hunan Province,which showed the excellent shale gas prospect of the plate edge.The study can guide shale gas exploration direction in Northwest Hunan Province,and can also provide a reference for similar geological conditions in Southern China.