Study On Accumulation And Transmission Law Of Deep Containing-Water Shale Gas Reservoir

There is great potential for deep shale gas resources in China,which is an important field of unconventional oil and gas replacement development.Shale reservoirs generally contain a certain amount of connate water,and a large number of subsequent intrusive water represented by fracturing fluid are retained in the subsequent development process,resulting in unclear adsorption law of deep water-bearing shale gas reservoirs under high temperature and high pressure.the microscopic gas-water two-phase transmission mechanism in the development of shale gas reservoir needs to be further studied.First of all,based on the study of the adsorption characteristics of deep water-bearing shale gas and the equilibrium water isothermal adsorption experiment,this paper preliminarily defines the adsorption law of deep water shale gas from the four angles of organic and inorganic pores,connate and intrusive water.Then the typical adsorption model of deep shale is constructed by means of molecular simulation and the distribution characteristics of water molecules are analyzed.The adsorption data based on simulation fit well with the experiment.Furthermore,the influence mechanism of different types of pores and different types of water on methane adsorption of deep aquifer shale in the full temperature and pressure domain was studied by model epitaxy.Finally,the mechanism of gas-water two-phase transport in micro-and nano-scale is studied by non-equilibrium molecular dynamics,and the effects of temperature,water saturation and pore diameter on two-phase flow are explored.The results show that for shale,montmorillonite,Illite and organic matter,the adsorption capacity is reduced to 50%60%under the condition of balanced formation water（Sw=15%）,and the fracturing fluid is reduced to 30%40%under the same conditions.It is found that the effect of high temperature and high pressure on the adsorption of water-bearing shale is not obvious.For different types of pores,the effect of water molecules on the pore adsorption capacity of montmorillonite,Illite and organic matter increases with the increase of pressure.At 80℃and 71MPa,the adsorption capacity decreases to 40%55%and 60%respectively,and the absolute value of the decrease is about 2 times that of montmorillonite and 4 times that of Illite.Under different water conditions,the effects of water molecules on methane adsorption in deep shale under high temperature and high pressure are in the following order:bivalent Ca²⁺Mg²⁺ionized water>monovalent Na⁺K⁺ionized water>fracturing fluid.Through the study of the gas-water two-phase flow process under the conditions of 50℃～110℃and pore diameter 30/50,it is found that the temperature and pore size have no obvious effect on the methane flow in the intermediate region,and the velocity is basically kept at 1（?）/s.For different water-bearing conditions,the flow of water and methane molecules form a"double competition"relationship.At low water saturation,water molecules are basically in a state of bound water,and the promoting effect of"surface competition"is dominant.The velocity of methane molecules in the middle region is 40%higher than that in anhydrous conditions.When the water saturation is high,part of the water changes into flow dynamics,and the inhibition effect of"spatial competition"is further improved but not dominant.on the whole,the flow rate of methane molecules in the middle area increases by 16%.The flow rate of water molecules at high water saturation is only 42%of that of methane molecules.