Research On Deep Solution Of A New Acidizing Fluid System On Water Injection Wells

The reservoir of P oilfield is a multi-layer sandstone reservoir,which has the characteristics of loose cementation,high porosity,high permeability and strong heterogeneity.What's more,the water injection development is the main development type of the target reservoir.Because of the limited water treatment capacity of offshore oil field,the injection water quality index exceeds the standard,which leads to the serious damage of water injection wells,and the water injection capacity decreases rapidly.Acidification is one of the main methods of plugging,which plays an important role.However,when the multiple acidification injection wells is re-acidized,the blocking effect and the effective time are gradually shortened,the difference of permeability layer also increased.So,it is essential to carry out a new plugging removal technology to ensure the efficient development of oil fields.Therefore,it is necessary to research a new type of high efficient acidizing fluid system to achieve the goal of plug removal and injection,to prolong the period of acidizing and even acidification.On the basis of the research on the composition of the target reservoir rock and the analysis of the reservoir,the reservoir physical property and fluid property,the following research works has been carried out:1)The overall performances of the new type of solution are proposed,which is based on deep plugging,low damage and effective steering.According to the design principle and screening of composition and concentration of the acidizing fluid system,a new type of acidizing fluid system was developed,which is suitable for the target reservoir acidizing.The composition of the new acidizing fluid:Main acid + diverting agent + other additives.2)The comprehensive performance evaluation of the new acid system was carried out,which based on the characteristics of deep plugging,low damage and diversion:(1)The research on deep plugging properties shows that the acid fluid system has strong corrosion ability of reservoir matrix and blockage;the research of multiple ionization characteristics,film-forming properties and residual acid effective time shows that new acid system can slowly release hydrogen ions,reducing the velocity of acid rock reaction and acid fluid system deep penetration.(2)The research on low damage characteristics of the acid system shows that the new system can effectively chelates metal ion in a wide range of pH.The acid system has excellent performance in the inhibition of two precipitation;the combined with the corrosion rate of reservoir temperature(60 centigrade)and micro scanning imaging,shows that the acid system can meet the the low corrosion rate of acid solution of the design requirements.(3)The diversion characteristics research shows that viscosity of the solution gradually increased and then decreased with the increasing concentration of hydrochloric acid;the micro micelle size and pore structure of agent molecules of the acid system is changed with the concentration of hydrogen ions in the solution;it has excellent performance of partial degradation of heavy oil,broken the glue completely and effectively steering.3)The acidizing effect of the new acid system on the target reservoir was evaluated by the long core acidizing experiment.Single core acidizing effect,the residual acid ion concentration analysis and acid plugging depth determination were verified that the new acid system has good characteristics of deep plugging and low damage characteristics.Double core parallel flow experiments show that the acid system can effectively reduce the permeability difference between the cores,reflecting the performance of great diversion effect.The re-acidizing experiments show that the new acid system can effectively remove the plugging damage in the acid water injection wells,and the plugging effect is better than that of the conventional acid system.Through the researchs,the new acid system for target blocks can effectively improve the reservoir acidizing plugging effect,prolong the availability period and decrease the differential permeability between layers.It has the important practical application value for the effective injection of the target oil field.