Stduy On The Model Of Fluid-solid Coupling Of The Numerical Simulation On Shale Gas Reservoirs

Shale reservoir has the low porosity and low permeability characteristics.To obtain ideal production,shale reservoir needs to form a certain artificial fracture.In the process of shale gas extraction,with the reservoir fluid is extracted,the pressure of the reservoir also decreases.These increase of effective stress,compression of pore pressure and decrease of permeability.The decrease of reservoir pressure will lead to the hale gas desorption,which is in adsorption phase,caused matrix contraction.As a result,the fracture and permeability are all increased.Therefore,this paper synthesize Shale gas reservoir occurrence mode,Percolation characteristics of shale and Fluid field caused by pressure drop in the process of hale gas extraction and coupling between deformation fields.According to the constitutive equation of elastic mechanics,the stress field governing equation of shale reservoir is derived,and the two-phase flow equation and the channeling equation in matrix fracture are derived according to the material equilibrium equation of fluid and Langmuir isothermal adsorption equilibrium equation of shale gas reservoir.Based on the elastic theory of porous media,the dynamic model of physical parameters of shale gas reservoir is established,including porosity dynamic model and permeability dynamic model.Combined above equations,finally,the mathematical model of gas-water two-phase fluid-solid coupling in shale gas reservoir is established.At the same time,the numerical simulation of the model is carried out by using Consul multi-physical field simulation software,and obtained the following main results and conclusions.(1)By analyzing the model of shale gas reservoir without fissures,the results show that in the early stage of production,due to the high pressure gradient of wellhead and gas reservoir,the gas velocity is higher,and the gas production is higher.With the increase of production time,the pressure gradient becomes slower,the pressure in the gas reservoir gradually decreases,and the production rate decreases.The permeability and porosity decrease caused by the coupling effect,which results in a large decrease in production compared with the non-coupling rigid model.(2)By analyzing the model of microscopic mechanism fracture,change the inlet pressure and outlet pressure.In the end,the surface fluid pressure generates deformation effect.When the pressure of fluid gradually decreases,the gap between fractures becomes smaller.At the macro level,the permeability is reduced.The production of shale gas can be overestimated by mining model without fluid-solid coupling.(3)Compared the different three types of shale gas reservoir model these are fracture,opening,and the length.When the fracture azimuth is not at the same direction,the diagonal Angle between crack and injection-production well is smaller,the gas impact area is more.When the fracture direction perpendicular to pressure gradient,it will has adverse effect on the production.Crack opening effect on mining area will appear similar to acupuncture effect,when the crack is not reached in the area affected by mining;the degree of crack opening hinders the advancement of the area affected by mining.However,when the mining affected area is punctured by cracks,it will accelerate the mining impact area.For the cracks of different lengths,the fissures are longer,influence area is wider.When there are fissures with the same direction as the gas pressure gradient in the gas reservoir,the longer the fissures length,the more obvious the gas pressure in the gas reservoir will decrease,and the larger the influence area will be.If the gas reservoir contains cracks perpendicular to the direction of gas pressure gradient,it will have adverse effects on production.(4)For the dual porosity medium medium shale gas model with artificial fissures,the cumulative production will be overestimated to a certain extent when the pore medium deformation is not considered.(5)For the dual porosity medium shale gas model with natural fissures,the through fractures are compared respectively.The results show that the existence of the penetrating fracture will greatly strengthen the mining influence area.