The Occurrence State And Seepage Law Of Gas And Water In Shale Gas Reservoir

With the increase in economic income,people's demand for energy is getting higher and higher in recent years.The consumption of oil and natural gas in China is next only to the United States,but production is always in short supply.People's awareness of environmental protection is growing,meanwhile,natural gas,as a less polluted source of energy,has been paid attention to most of people.However,due to the limitations of mining technology,The proven reserves of natural gas in China is not abundant,which has accounted for only 2.1% of the world's total proved reserves.Shale gas is a new type of unconventional energy,with the characteristics of a wide range of resources,large amount of resources,long production life,stable production and so on.The United States and Canada have achieved commercial development of shale gas.China's proven reserves of shale gas are rich,with great potential for exploitation and the annual capacity of 10 billion cubic meters formed.China has become the third country,which achieves commercial development of shale gas.Although China has been rich in shale gas resources,due to the limits of China's geological conditions and the lack of the theoretical knowledge about research,resource exploitation starts late.The study of this paper is to carry out theoretical and experimental research on the basis of the production situation in the field.Based on the nanoscale pore characteristics of shale matrix,the influence of the diffusion,slipping and darcy seepage of shale gas in nanopores on shale gas flow are analyzed.The diffusion effect and the slipping effect of the gas under the low pressure are obvious,the proportion of the flow generated by the diffusion is larger and the seepage under the high pressure is mainly the west flow.At the nanometer scale,the shale gas is stored in the shale reservoir in condensed,free and adsorbed states and the new formula for calculating the shale gas reserves is given according to the proportion of shale pore size distribution.According to the feedback from field,the liquid discharge rate is very low after the hydraulic fracturing,which has a great impact on shale gas production.Based on the study of the occurrence state of water in shale,the experiment of water infiltration in shale and the displacement experiment of gas in saturated water core are designed to summarize the influence of water on gas seepage.The experimental results show that the water is deeply divided into three stages in the shale.Firstly,the water ring is rapidly formed at the interface of the shale-water-air.Secondly,when water flows in the cracks in the shale surface and the micro-cracks in the seepage,the mass of water remains constant.Gas flows in the dry core without the starting pressure gradient and in the saturated water core with the starting pressure gradient,whose average starting pressure is 1.26 MPa.The research above has laid a theoretical foundation for the characteristics of fracturing fluid backfill,gas seepage characteristics and reasonable forecasting capacity in the development of shale gas in China.