Dynamic Simulation Of Injection Water In Micro-fractured Well

In the late stage of the development of offshore oilfield,the formation energy deficit is large,and the bottom hole pollution is serious,so the water injection pressure is rising fast and the effect is poor.In order to solve this problem,based on the theory of elastic mechanics and seepage mechanics,heat conduction,crack extension theory and the three field coupling theory,this paper established a crack extension model of micro-fracturing augmented injection process as the background of the Bohai oilfield.The thermo-hydro-mechanical coupling effect of long-term water injection is considered in this model.The effect of the thermal effect is mainly manifested in the cooling effect of the long-term injection of cryogenic fluid on the reservoir,and the effect of pore elasticity is caused by the extrusion of the fluid entering the pore space of the rock.Then the process of fluid flow not only reflects the ability of seams,but also embodies the function of energy transfer.It is also one of the direct causes of rock defonnation.In the process of solving the problem,firstly,the finite difference method is used to make the difference between the crack propagation equation,the material balance equation,the two-phase seepage equation and the temperature field equation.Then,the three field coupling Matlab program is compiled under the specific boundary condition.Finally,based on the calculation results,the two aspects of the fracture morphology and the effect of increasing injection are analyzed,and the following conclusions are obtained:(1)Based on the theory of elastic mechanics,seepage mechanics and heat fluid-solid coupling,the them-no-fluid-solid coupling model between the dynamic expansion of high permeability reservoirs in the sea and the reservoir matrix is established.(2)On the basis of the micro-fracturing injection model,the non-fracturing injection model was established.By comparing the calculation results under two models(bottom hole injection pressure),the micro fracturing augmented injection technology after bottom hole injection pressure and the fracturing augmented injection model was significantly less than the bottom hole injection pressure,show that micro fracturing augmented injection technology compared with not fracturing augmented injection.(3)The injection pressure decreases with the increase of permeability and porosity,and increases with the increase of elastic modulus,Poisson ratio and injection fluid viscosity;Has a great influence on coupling effect of bottom hole injection pressure,under the influence of different coupling bottom hole injection pressure size exists P-N(no account of heat flow and solid coupling)>P-HM(considering fluid-structure interaction)>P-THM(consider the impact of heat flow and solid coupling);The pressure value of injection pressure at the bottom of the well is greater than that at the bottom of the well.(4)When the permeability and porosity are larger,the fracture length is shorter;When the displacement,injecting fluid viscosity,injection time,elastic modulus and Poisson’s ratio are higher,the length of crack length is longer.When considering the different coupling effects,the length of the crack is L-N(regardless of the heat flow solid coupling)>LHM(considering the fluid-solid coupling)>L-THM(considering the thermo-fluid-solid coupling);At any time,the crack length obtained under the closed outer boundary condition is greater than the crack length obtained under constant pressure.(5)For F8 well,during the process of micro-fracturing,the hydraulic fracture will not communicate the fault,thus it will not pose a risk to the development of the oil field.