Study On The Rising Law Of Polymer Injection Pressure And Blockage Mechanism In Polymer Injection Wells

Polymer flooding is an important technical to ensure stable production and high efficiency production in target A oilfield.It is also the most important measure to increase production in target A oilfield at present.However,with the increase of polymer solution injection,the problem of increasing injection pressure in polymer injection wells is becoming more and more prominent,such as serious formation blockage,decrease of liquid production and excessive increase of injection pressure in polymer injection wells.The injection pressure of some wells is close to or reach the fracture pressure of oil layer,but it still can't meet the requirement of injection allocation,which will affect the displacement effect of polymer solution.In this paper,the increasing regular pattern of polymer injection pressure and blockage mechanism of polymer injection wells in target A oilfield have been studied,and the following research results have been obtained:(1)The present situation of pressure rise in polymer injection wells in target A oilfield is statistically analyzed.The results show that the injection pressure rises in most wells,the maximum rising pressure is 7.20MPa,and the potential damage analysis of the reservoir is carried out.The results show that the migration of particles,the cross-linking of precipitate and iron ion with polymer may cause formation blockage.(2)The study on the increasing law of injection pressure of polymer solution shows that the increase of viscosity of polymer solution will increase the injection pressure of polymer solution by a large margin.The static adsorption capacity of polymer solution with different concentration was measured by starch-cadmium iodide method.The results showed that the static adsorption capacity increased with the increase of polymer concentration.The core displacement experiments with different adsorption retention rates show that the larger the adsorption retention amount,the higher the polymer injection pressure,and the theoretical analysis shows that the injection pressure will be increased by the inaccessible pore volume of the polymer.(3)The effect of insoluble matter on polymer injection pressure was measured by core displacement experiment.The results showed that the injection pressure of polymer solution increased with the presence of insoluble matter.The steady pressure and follow-up water drive pressure are 0.15MPa and 0.01MPa higher than those of the polymer solution without insoluble matter,respectively.The experimental results show that when the concentration of Fe3+reaches 3mg/L and CaC12 solution,the concentration of MgC12 solution reaches 400mg/L,the polymer solution will produce the flocculate and the micelle,and the possibility of formation plugging is increased.The displacement experiment of polymer solution with different degree of dissolution shows that the smaller the degree of dissolution,the larger the injection pressure,the injection pressure of polymer solution with 50%solubility is 1.03 MPa higher than that with 90%solubility.(4)According to the change of injection pressure and fluid flow rate when the core is blocked,a method for evaluating polymer blocking degree under constant velocity injection is established.The blocking mechanism of polymer under different conditions is studied by displacement experiment.The results show that the polymer blockage law under different conditions has been studied by displacement experiment.The higher the concentration of polymer solution,the higher the injection rate,and the smaller the permeability of porous media,the greater the blocking degree of polymer.(5)Under the condition of constant pressure,the blocking effect of polymer is evaluated according to the flow rate of liquid,and the corresponding evaluation index is obtained.When the pressure gradient is 0.05MPa/m,the blocking effect of polymer is evaluated according to the pressure gradient.When the judging limit of polymer solution injection ability is set to 0.05mL/min and the flow rate of polymer solution is greater than 0.05mL/min,the polymer solution injection performance is good and no blockage will occur.The research results of this paper further improve the regular pattern of polymer solution injection pressure rise and the mechanism of blockage,and further elaborate the relationship between injection pressure rise and blockage.The established polymer clogging degree evaluation method provides a powerful theoretical basis and technical support for the evaluation of polymer application,and provides a new technical method for the study of polymer blocking mechanism.