Study And Simulation For Fracturing Fluid Influence On Hydrocarbon Migration Characteristics

In the process of low-permeability and ultra-low permeability oil and gas fields,it is necessary to carry out volumetric fracturing transformation through artificial hydraulic fracturing technology to improve oil recovery.However,the current back-flow rate during back-flow construction operations is usually less than 30%.The fracturing fluid cannot be returned to the tank and eventually stays in the reservoir.The retained fracturing fluid will undergo physical and chemical changes under the factors of reservoir temperature,pressure,formation mineralized water,residence time and lithology composition,and finally affect the hydrocarbon migration of the reservoir.Based on the above background,the lattice Boltzmann method is used to comprehensively consider the factors of methane adsorption desorption,slippage and external force,and simulate the flow of methane in the formation.The adsorption morphology of fracturing fluid in the reservoir was further investigated,and the flow of shale gas after fracturing fluid retention was simulated.The influence of fracturing fluid retention on hydrocarbon migration was studied.(1)Simulation of shale gas flow by lattice Boltzmann method shows that porosity and pressure are the most important influencing factors in shale gas seepage,and porosity has the most obvious influence on permeability.(2)When shale gas flows at the micro-nano scale,it is accompanied by adsorption desorption,diffusion,surface slippage effect and external force factors.It is found through simulation that the surface slip effect will increase the permeability;shale gas adsorption desorption and diffusion on shale The influence of gas flow is not significant;external force factors in the flow of shale gas will reduce the permeability.(3)After the fracturing fluid is retained,it will adsorb on the single layer of the shale wall to form a bound water film,which will cause the porosity of the shale reservoir to decrease and the pore size to become smaller.The simulation found that the retention of fracturing fluid will lead to an increase in external force,which will result in a decrease in flow velocity and a decrease in permeability during shale gas flow,which will adversely affect shale gas migration.The bound water film formed at the wall surface enhances the surface slippage effect when the shale gas flows.When the porosity is high,the slippage effect is not obvious,and the retention of the fracturing fluid reduces the flow velocity,which is not conducive to shale gas migration,but in the pores.When the rate is low,the slippage effect is obvious,which is conducive to the hydrocarbon migration,and becomes a positive factor affecting hydrocarbon migration after the retention of fracturing fluid.But generally speaking,the retention of fracturing fluid reduces the migration speed of oil and gas,which is not good for on hydrocarbon migration.