Analysis On The Influence Of Polymer Sewage Reinjection For Oil Layer Injection Capacity And Its Countermeasures

As for the oilfield sewage reinjection system, the concentration of suspended material in injected water is an important index to evaluate water quality. How to determine the index of oil content and suspended material according to specific reservoir is the key to developing oilfield water injection development.This article has firstly analyzed the injected water quality by using sewage water samples,which are obtained at the wellhead, then core flow experiments are carried out to determine the water quality index of the reinjected sewage; and finally the feasibility of powder nitric acid acidification technology is determined by using the evaluation experiments of plugging removal effect. It can be indicated from the results of core flow experiments that the greater the concentration of suspended material is, the higher the damage degree of core will be; the greater the PV number of injected sewage is, the greater the degree of plugging of core will be;the greater the core permeability is, the smaller the loss of core permeability. For formations whose gas permeability is between 150 mD, and when the allowable damage rate is 50 %, the proposed water quality index limits areas follows: the concentration of suspended material is4.8mg/L; For the formations whose gas permeability is between 450 mD, when the allowable damage rate is 50 %, the proposed water quality index limits are: the concentration of suspended material is 15.24mg/L. For the formations whose gas permeability is between 300 mD, when the allowable damage rate is 50 %, the proposed water quality index limits are: the concentration of suspended material is 48.33mg/L. The plugging removal experiment shows that the powder nitric acid acidification technology has good performance in removing plug.The permeability recovery rate was higher than 70% when the degree of blockage was below100%, but the fracturing measures were recommended when the blockage degree of the low permeability reservoirs below 300 mD was more than 70%. The achievement of this article would have instructive influence on setting water quality index on site.