Study On Resources Potential Of Shale Gas In Carboniferous And Permian Formations In South Central Hunan Province

This paper selected the Lower Carboniferous Series Ceshui Formation and The Permian Series Longtan Formation shale as the main object in the in south central Hunan province. Through a variety of means of experimental tests.This paper focus on deposition distribution characteristics, geochemical characteristics, Reservoir physical property characteristics and Resource potential characteristics of shale in the study area were studied and analyzed. Based on this forecast shale gas better conditions favorable area. Results and conclusions were as follows:1.This study concluded the sedimentary environment and spatial distribution characteristics of the shale of lower Carboniferous Ceshui group and upper Permian Longtan group in studied areas through the data investigation and field survey,it showed that the Ceshui group is widely distributed(in studied areas),and its lithology is coastal to coastal marsh sediments which is mainly made up of a littoral clastic rocks.The Ceshui group can be divided into two sections and the upper section is the main hydrocarbon source rock.The thickness of the Ceshui Formation in the up is between 20 and 133 meter and those deposited in Lianyuan and Loudi which is larger in the middle of Hunan province and Muxian areas in the south of Hunan,and the thickness is more than 100 m.The mud shale of the lower segment of Longtan Formation deposited mainly in tidal flat,barrier tidal flat, shallow deep sea environment,and the thickness of this mud shale is between 30 and 200 m.The mud shale is thicker in Xinhua and Shuangfeng areas which is in the middle of Hunan province and Yongxing and Zizhou areas which is in the northern Hunan province,most of the thickness is more than 100 m.2.This paper a series of geochemical analysis to understand the primary characteristics of shale in study area. Organic matterof shale in Ceshui Formation is primary type Ⅲ,organic carbon content in the range of 0.84 to 5.2, with an average of 2.7. Higher maturity, minimum of Ro is 1.95%,maximum is 9.5%,mean is 3.06%. Organic matter of shale in the lower segment of the Longtan Formation is primary type Ⅰ(Sapropel).There are large variations of organic carbon content in between 0.07% to 13.37%,with an average of 4.65%,Ro is universal high,minimum of Ro is 0.9%,maximum is 7.88%,mean is 2.78%.In summary, the geochemical characteristics of shale in Ceshui and Longtan Formation of study area are more conducive to the enrichment of shale gas.3.Through the systematic laboratory work this paper found that the shale in Ceshui and Longtan Formation of study area have the preferably brittle characteristics, Brittle mineral content of quartz, feldspar, mica are very high. Joints and fractures are well developed, tensional cracks are common, followed by compressive cracks, shear cracks are rare. The hole is commonly developed, but the distribution is uneven. porosity is in range of 0.7% to 13.2% and it is in the middle level, with an average of 2.4%, Penetration is generally low, mostly in the 0.2 × 10-3μm3 the following. Average pore size is between 4.348 nm and 22.4nm, with an average of 13.91 nm. Specific surface area is between 0.464m2 / g and 19.81m2 / g, with an average of 2.342m2 / g. The total pore volume is between 0.00121 ml / g and 0.0179 ml / g, with an average of 0.00650 ml / g,Porevolume is larger. The biggest contribution to the total pore volume and specific surface are tiny pores, up to 90.18% and 94.92% on average. High specific surface area and high pore volume are conducive to the occurrence of the shale gas. The pore morphology is mainly hole II which is closed at one end and airtight, there are also an open class I hole and mutually inclined parallel plate slit pore, there may be a small amount of ink bottle hole4.After the comprehensive study of the main geological characteristics of shale of Ceshui Formation and Longtan Formation in the studied areas,we have predicted that the shale gas resources of Ceshui Formation in the studied areas and between 0.234×1012 and 0.465×1012m3, the resources of Longtan Formation between 0.259×1012 and 0.514×1012,and the prospective Resources are between 493×1012 and 0.979×1012m3 in all.We also have predicted three advantageous areas of lower Carboniferous Ceshui group that are Lianyuan,Loudi and Youxian which is in the middle of Hunan province and two advantageous areas of the upper Permian Longtan group that are Xinhua which is in the middle of Hunan and Anren and Zixing areas in southern Hunan province by comprehensive analysis.