Effect of water occurrence on shale seepage ability

Due to the strong water absorption of clay minerals, the original water-bearing state of shale reservoirs changes after hydraulic fracturing, and the seepage capacity is affected. Based on nuclear magnetic resonance (NMR) technology and fluid state experiment of water-bearing shale, the distribution characteristics of water in clay minerals and shale were obtained, and the influence of water occurrence on shale seepage capacity was quantitatively analyzed. The results show that water is mainly adsorbed on the surface of clay pores in the state of bound fluid. In the early stage of shale water absorption, water mainly occurs in the form of bound water film on the pore surface of clay bound fluid with 0.02 mu m < r < 0.46 mu m. In the later stage of shale water absorption, water mainly occurs in the form of bound water film and capillary column in the pores with 0.02 mu m < r < 5.79 mu m. Water saturation is the main control factor affecting shale seepage capacity. When the water saturation of shale is about 60%, the shale permeability can be reduced by about 50% on average. At the same time, the effect of water occurrence on shale seepage capacity is more significant under low water saturation. Under low water content (Sw<25%), the existence of bound water film on the pore surface of clay bound fluid is the main reason for the decrease of shale seepage capacity. Under high water content (35%<65%), the bound water film and the capillary water column in the pores of capillary bound fluid jointly lead to the decrease of shale seepage capacity, and the effect of bound water film on shale seepage capacity is more significant. This study clarifies the water distribution characteristics of shale with different water saturations, clarifies the influence of water occurrence on shale seepage capacity, and provides reference for shale gas development.

Automated summary

This study utilizes nuclear magnetic resonance (NMR) technology and fluid state experiments to analyze the distribution of water in clay minerals and shale and its impact on permeability. The results show that water saturation is the main factor affecting shale seepage capacity, with the existence of bound water film being a significant factor under low water saturation.