Investigate On Gelling And Plugging Properties Of Polymer Gel In Porous Media

After a long period of water injection development,most of China’s oil fields have entered high water cut stage and extra high water cut stage.Profile control and water plugging is one of the main measures to solve the high water cut.Among them,the polymer gel is a widely used profile control and water plugging agent.The commonly used evaluation method of gelling performance of polymer gel is to cross-link polymer solution into gel under indoor static conditions and determine its viscosity,strength and stability.The plugging performance of gel is determined by core/sand filling tube experiment,and the shear resistance of gel is evaluated by rotating stirring method.However,there is no research on the gelation and plugging performance of polymer gel in porous media.Therefore,this paper studies the characteristics of polymer gel in the stratum through experiments and numerical simulation.The gelation time and viscosity were evaluated,and the concentration of the formulation was optimized.The multi-PV injection gel experiment of the sand filling tube was used to study the injection pressure of gel under different permeability and injection amounts,and the viscosity of gel at each point was calculated.The oil displacement experiment was carried out by using a three-tube parallel connection,and the plugging performance and enhanced oil recovery effect of different slugs were compared and explored.Through reservoir numerical simulation,the plugging effect of polymer gel in the formation is simulated,and the injection parameters are optimized.The optimal formula was 0.3%～0.4%polymer+0.3～0.4%cross-linking agent+0.2%～0.4%curing agent+0.05%～0.2%additives.The gelation time was about four days,and the viscosity was more than 20000 m Pa·s.The optimized formula of multi-PV was injected into the sand filling tube,and the results showed that the adsorption retention and shear thinning of the porous media in the sand filling tube on the polymer gel led to a large difference in the gel viscosity at the injection end and the recovery end,and the viscosity ratio between the injection end and the recovery end could reach 56.5.And the higher the permeability,the smaller the viscosity ratio,the greater the injection volume,the greater the viscosity ratio.Through microscopic analysis,polymer molecules are adsorbed,retained,accumulated and intertwined at the injection end,and further cross-linked to form a dense spatial network structure.Macroscopically,the viscosity of polymer at the injection end is greater than that at the production end,and the polymer concentration is different.The slug design of polymer gel was optimized by a three-tube parallel plugging model experiment.The inverted triangle slug preferentially uses a high concentration slug to block the high permeability pipe,and then uses a low concentration slug to achieve the best sealing effect with less polymer dosage,which can increase recovery by 15.7%.Finally,through the reservoir conceptual model,the difference between the plugging effect of the polymer gel after formation shear and the polymer gel without shear is clarified,and the injection parameters are optimized.The optimal injection volume of plugging agent is 2600 m~3,and the optimal injection timing is about60%～75%of water content.