Studies on the structures of pores and fractures in shale reservoirs and the characteristic differences between marine and continental shale reservoirs

In order to analyze deeply the characteristic differences and gas bearing potential of microscopic pores in marine and continental shale, high vacuum scanning was carried out on shale samples by using FEI Quanta 200F field emission environmental scanning electron microscope (FE-ESEM), and the structural systems of microscopic reservoirs pores were established. Then, the gas storage capacity of different pores and the their controlling effect on the seepage and diffusion of shale gas were investigated based on the size, morphology and connectivity of microscopic pores observed through SEM, combined with the former research results of shale adsorbed gas and free gas and the characteristic differences between adsorbed gas and free gas. The microscopic pores in marine and continental shale were compared. And finally, the characteristic differences and gas bearing potential of microscopic pores in marine and continen-tal shale were summarized. It is indicated that among 6 types of pores in shale gas reservoirs, adsorbed gas is enriched in the organic nanopores and the intergranular pores in clay minerals, and free gas is enriched in the pores in paleontologic fossils, mineral pores in rock skeletons, the intercrystalline dissolved pores in pyrite and the microfractures. The reworked mineral pores in rock skeletons and microfractures play an important role in the seepage and diffusion of shale gas. The content of organic matters and organic nanopores in marine shale is much higher than that in continental shale, and nanopores are enriched with adsorbed gas. There is more quartz, feldspar and carbonate minerals in marine shale, so the content of fragile minerals in marine shale is higher than in continental shale, and consequently marine shale can be fractured easily. Based on above-mentioned two factors, therefore, the development potential of marine shale is higher than that of continental shale.