Fracability Evaluation Research Of Shale Reservoir In North-western Hunan Province

Shale gas is a huge global resource with the potential for exploration and development.Domestic scholars focuse on the accumulation mechanism,enrichment conditions and favorable region of shale gas.But studies on reservoir stimulation methods are fewer.In this paper,experimental research and theoretical analysis of reservoir Characteristics of shale gas in North-western Hunan province are carried out.Evaluating the fracability from qualitative and quantitative perspectives.The main work are as following:(1)Research on geological characteristics of shale in North-western Hunan province.The geological survey results show that shale has become black carbonaceous slate,silty carbonaceous slate and dark gray,dark gray thin bedded siliceous rocks.The results of Mineral composition and microstructure through scanning electron microscopy and X diffraction experiment show that the average content of brittle minerals are 63.6%,higher in the same level,while the average content of clay minerals are 29.4%,containing a small amount of kaolin;Reservoir and a lot illite.Micro fractures of the shale in North-western Hunan Province are developed,containing a large number of small holes and a honeycomb like strawberry.Density of slot system is high.(2)The physical and mechanical properties of the shale in North-western Hunan province are researched.The physical experiment results show that the density of shale is between 2.16g/cm~3~2.46g/cm~3 and the Water content and saturated water absorption rate are respectively 0.615% and 0.888%.The uniaxial compressive strength of the shale is between 78.04MPa~161.23 MPa.The average vale of Young's modulus and Poisson's ratio are respectively 31.8GPa and 0.23.There are no obvious plastic deformation and yield points of Stress-strain curve,which indicates Brittle failure.Three axis test results show that the failure mode of shale under different confining pressures is shear failure and the Peak stress is between234.429MPa~324.478 MPa.The tensile strength of shale is between4.10MPa~15.14 MPa.The main damage form is tensile along the axis.(3)Establishment of fracturing evaluation model.In this paper,the fracturing properties of shale in the northwest of Hunan are quantitatively evaluated by several key indexes,such as shale coefficient,brittle mineral content,clay mineral content and cohesion.The weight coefficient of different indexes is calculated based on the principle of Analytic Hierarchy Process.The non-dimensional constant is normalized from 0 to1,and the fracturing coefficient of shale gas reservoir in northwestern Hunan is calculated based on the basic data provided by physical mechanics test.It is found that the fracability of shale in northwestern Hunan is in the middle level according to the classification of the fracturing coefficient and through the comparative with the fracturing coefficient of shale fractures in Shengli Oilfield.