Study On Concentration Effect Of Polymer In Reinjection Sewage And Its Damage To Reservoir

On the one hand,polymer flooding increases oil recovery and crude oil production;on the other hand,the sewage contains a certain amount of HPAM,which greatly increases the difficulty of sewage treatment.The remaining HPAM will cause some damage to the reservoir when the sewage is reinjected,the permeability of the reservoir will obviously decrease.Therefore,it is very necessary to measure the indicators of the polymer-containing sewage and analyze the influence of the polymer concentration on the indicators,determine the damage of HPAM to the reservoir during the injection.In this paper,the polymer concentration,oil concentration,concentration of suspended solids,particle size of suspended solids,static adsorption concentration,conductivity and infrared spectroscopy of polymer were obtained by analyzing of water quality in different areas of the oilfield,which provides basic data for sewage treatment in oilfield.On this basis,the effect of polymer concentration on the indicator was obtained by comparing the indicators of different polymer concentration areas.The study found that with the increase of polymer concentration,oil concentration,concentration of suspended solids,particle size of suspended solids,static adsorption concentration have increased significantly,while the conductivity is basically unchanged.The effects of injection volume of polymer,polymer concentration and air permeability on the loss of core permeability were further studied through core flow experiments,and it was found that the loss of core permeability increased when injection volume of polymer and polymer concentration gradually increase,and decrease when the air permeability gradually increase.Based on the results of the core flow experiment,loss of core permeability is 30%as the limit,concentration range of the polymer during the reinjection was obtained.From 2019 to 2022,the damage of injected polymer to the reservoir is less than 30%.From the start of reinjection of polymer-containing sewage to 2025,the polymer concentration should be controlled to less than 78,90,111 and 150 mg/L for reservoirs with air permeability of 100,200,300,and 400 mD,respectively.The damage of the reservoir with air permeability of 500 mD is less than 30%at the planned injection concentration(180 mg/L).Reservoir damage is evaluated and predicted with different permeability at the present stage and future stage:the damage of the polymer to the air permeability of 100,200,300,400 and 500 mD was 8.37,7.31,5.80,3.33,and 4.03%,respectively.However,when the polymer continues to be injected until 2025(the polymer concentration reaches 180 mg/L),the damage of the polymer to the air permeability of 100,200,300,400,and 500 mD is 51.56,40.65,38.24,31.19 and 27.76%.The mathematical equation that indicated the relationship among loss of core permeability,injection volume,polymer concentration and air permeability was established.Loss of core permeability can be obtained through this equation when the injection volume is any value between 0-3 PV,the polymer concentration is 0-200 mg/L and air permeability is 100-500 mD;The maximum concentration of polymer can be obtained when the value of loss of core permeability is given.