| Nowadays,most oil fields in China are in the late stage of water flooding development,and chemical flooding has become an important measure to improve oil recovery.The data showed that the EOR method can increase the recoverable oil reserves by 1.18 billion tons,and the chemical flooding method can cover 76% of the reserves,among which the polymer flooding technology is the most widely used.In actual production,in order to improve the injection capacity of polymer injection wells,injection pressure is often increased as much as possible.At this time,induced fractures more or less appear in the near well zone.On the one hand,the permeability near the well is increased,and on the other hand,the heterogeneity of the reservoir is increased,which seriously affects the development effect of polymer injection.Using the advantages of numerical simulation technology,the numerical well test interpretation method provides a new idea and scheme for accurately describing and evaluating the dynamic characteristics of pressure in fractured wells induced by polymer injection.However,at present,there are few cases of using numerical well test method to study induced fractures considering polymer injection stage.Therefore,based on numerical well test interpretation method,this paper carried out numerical well test research on polymer flooding considering induced fracture.Firstly,literatures related to numerical well test methods were fully investigated,and PEBI variable scale hybrid grid was selected for spatial dispersion of the reservoir area.The mathematical models of polymer flooding vertical wells in homogeneous reservoirs and polymer flooding vertical fractured wells considering induced fractures were established by comprehensively considering the viscosity relationship of polymer solution,shear effect,permeability decline and adsorption mechanism.Finite volume method was used to discretize the mathematical model and GMRES method was used to solve it.The numerical solution of bottom hole pressure was obtained through MATLAB programming.The logarithmic curve of pressure and pressure derivative was drawn and the influencing factors were analyzed.The results show that the reliability of the numerical well test method is verified by comparing the numerical solution of bottom hole pressure with the analytical solution of vertical well with polymer flooding in homogeneous reservoir and vertical fractured well with induced fracture.Through the sensitivity analysis of numerical well test curve,it is found that the wellbore storage coefficient and skin coefficient mainly affect the early stage of well test curve.Polymer concentration,shear effect,permeability decline coefficient and inaccessible pore volume mainly affect the later stage of well test curve.The smaller the fracture half-length is,the more upward warped the pressure and pressure derivative curve will be.The larger the dimensionless fracture conductivity coefficient is,the more downward the curve moves,and the less obvious the characteristics of bilinear flow stage are.When the value of the fracture closure speed factor(delpat)is 0,the fracture closes rapidly.Because of the sudden change in pressure caused by the closure,it is shown as an obvious peak in the pressure derivative diagram.The larger delpat is,the slower the closure speed is,and the curve shifts to the right.The research results will further expand the pressure dynamic interpretation method of polymer flooding polymer injection well,enrich the related theory of numerical well test of polymer injection induced fracture well,and provide important technical support for accurately understanding the size and parameters of induced fracture. |
PDF Full Text Request