Study Of Pore Structure And Permeability Characteristics Of Marine Shale In Typical Area Of South China

The Marine shales of Wufeng-Longmaxi and Niutitang formation are the most important unconventional shale reservoirs in South China.In order to study the pore structure and permeability characteristics of shales,the combined technologies and methods of petrology,geochemistry,pore structure and permeability characteristics are used in this work to do some comprehensive research on geochemistry,pore structure,permeability and gas production calculation of Wufeng-Longmaxi shale in West Chongqing,Longmaxi shale in North Guizhou and Niutitang shale in South Sichuan.Moreover,the characteristics and exploration potential of shale reservoirs in different groups and regions are discussed.The development situation of mineral composition,organic matter content,organic matter type and thermal maturity of Wufeng-Longmaxi and Niutitang shales are discussed in this work through using the combined measurements on shale reservoir.The characteristics of inorganic pore structure,organic pore structure and microfracture structure of Wufeng-Longmaxi and Niutitang shales are analyzed qualitatively and quantitatively,and the difference of three shale reservoirs are summarized.The organic pores are the main storage space of shale gas.In order to study the organic pore structure well,the organic matter is extracted from the bulk shale.This method is feasible and efficient.The main controlling factors of the development of organic pores are discussed in this work.Base on the different thermal maturity of Wufeng-Longmaxi and Niutitang shales,the relationship between organic porosity and thermal maturity are established.The ability of organic pore producing of Wufeng-Longmaxi and Niutitang shales has reached the upper limit.With the increasing of thermal maturity,the volume and surface area of organic pore decrease.The thermal maturity is the main controlling factors on the development of organic pores,but it has little effect on inorganic pore structure.The study of thermal maturity is of great importance on generation and preservation of shale gas.The permeability parallel to the bedding of shales is higher than the that vertical to the bedding of shales.The difference in pore structure causes the strong anisotropic permeability of shale.The mineral composition and microfracture controls the permeability anisotropic ratio.The permeability model can effectively fit the experimental permeability data in this work.The pore compressibility and Klinkenberg constant have some relationships with the absolute permeability and the pore compressibility could reflect the stress sensitivity of shale.Permeability is one of the important parameters on evaluating the flow characteristics of shale and it affects the shale gas yield and capacity.Based on the basic parameters of shale reservoirs,a triple porosity model was applied in the reservoir simulator SIMED II to calculate the free and adsorbed gas production of Wufeng-Longmaxi and Niutitang shales.The pore structure and permeability characteristics are the main controlling factors on the productions of total gas,free gas in fracture,free gas in matrix and adsorbed gas.