Abstract:

Research on pore structures of shale gas is important to the study of shale gas evolution. Using the argon-ion milling-SEM technology this paper analyzes the pore type, pore shape, pore diameter and porosity of Doushantuo Formation shale reservoir in middle Yangtze area, and discusses the geological significance of these pores to oil and gas. Research results show that the shale in Doushantuo Formation can be divided into 4 types,i.e. organic pores, inter-granular pores, intragranular pores and microfractures. The pore morphology of shale can be divided into irregular polygon pores, round or oval pores, complex mesh pores, moniliforme pores, long-strip pores and striation pores. The complex mesh pore which has the best connectivity is conducive to the pressure transmission and can improve the desorption efficiency of shale gas and the permeability of reservoir. The shale pore diameter is 10 to 2 000 nm; the main range is 20 to 200 nm; the average porosity is 1.4% to 6.2%. Different types of pores can provide different-scale reservoir spaces for the occurrence of shale gas migration, and micro-fractures and intergranular pores are the most advantageous.

Key words: shale gas, reservoir, pore structure, argon-ion milling, scanning electron microscope