Research On Damage Removal Method Of Polymer Injection Wells For Heavy Oil Reservoir

Polymer flooding technology has been widely used and achieved great result in Bohai oilfield in China since 2003,It has become one of the effective ways to enhance oil recovery.In the process of long-term injection of polymer,the injectivity of injection wells are decreased by plugging,which cannot meet the requirements of injection program,and affecting the effect of development seriously.Meanwhile,long-term high-pressure operation also have some security risks of ground injection process.The key technology to ensure the efficient implementation of polymer injection is to reduce the pressure and increase the injectivity of polymer injection wells.Because of the complexity of the blockage and the particularity of the offshore oilfield,there have some problems about existing technology,such as low efficiency,short term of validity and high safety risk.In this paper,based on the analysis of plugging mechanism of polymer injection wells in heavy oilfield,with the thoughts of permeation swelling,stripping desorption,oxidation degradation and acid corrosion,through a series of measures synergies,an effective and safe compound blockage removal system was developed.(1)Based on the analysis of blockages,understand the main reasons for the damage of formation were the adsorption and retention of polymer,adhesive deposition of glial and asphaltene,and the form of inorganic sacle.The damage in the near wellbore zone is particularly serious,and the injection water quality exceeds the standard can also causes the damage in the formation which is difficult to relieve.(2)With the thoughts of viscosity reduction,polymer degradation,inorganic scale dissolution,optimized the reducing viscosity agent which can dissolve and strip the oil and organics from oily surface,reduce the viscosity of heavy oil;polymer degradation agent can reduce the viscosity of polymer solution and completely degrade the polymer gel.Inorganic scale dissolution agent can dissolve the inorganic scale and reservoir rock effectively.This compound blockage removal system has great compatibility with formation fluid,low corrosion rate,and can relieve the damage of core efficiently.(3)Combined with the characteristics of this blockage removal system,the alternating injection of gas and liquid technology was carried out.By this technology,the liquid can enter the deep of reservoir and expand the liquid spreading area,at the same time,it can increase the energy of formation which benefits for fluid flowback.(4)According to the results of laboratory experiments,field tests were carried out.After simulation,the production of oil and fluid were increased obviously,which indicates that the compound blockage removal system has remarkable performance on plugging removal and increasing oil production.The research contents and results obtained in this paper provide a strong technical support for solving the problems of plugging of polymer flooding wells on heavy oilfield.Meanwhile,it also provides a technical reference for other oil and gas wells.