Experimental study on optimization of acidizing fluid in heterogeneous oolitic limestone reservoir
The characteristics of shallow burial,thin layer,developed upper and lower water layers and strong heterogeneity lead to high difficulty on site reform of the oolitic limestone reservoir of Qianjiang Formation in Jianghan Oilfield.In order to optimize the transformation process and the best process parameters suitable for the reservoir,static dissolution experiments and acidification dis-placement experiments of two different acid systems of conventional acid and retarded acid were carried out.Combined with the analysis of CT scan results,the interaction law between oolitic limestone and different acid systems,the quantitative characterization of permeability changes at different injection rates and the three-dimensional imaging of acid-etched wormholes were clarified.At the same time,according to the results of acid rock reaction kinetics experiment and acid etching conductivity experiment,the effective distance of acid rock reaction in different acid system was predicted theoretically,and the acid system and injection parameters were optimized.The results show that the optimal mass concentrations of conventional acid and retarded acid are 20%and 10%,respec-tively.The displacement rate has no obvious difference in the increase of permeability after core acidification,but it has a great effect on the wormhole structure formed by acid etching.The increase of displacement rate makes the connectivity of wormhole better and the damage to rock skeleton smaller.Through the prediction and calculation of the effective action distance of the acid liquid,it is found that the effective action distance of the retarded acid is 11.87 m higher than that of the conventional acid under the same large displacement acid injection.Finally,according to the characteristics of the reservoir,an optimized large displacement injection of"10%retarded acid+0.3%corrosion inhibitor"acid system is found,which can effectively increase the acid action distance and enhance the transformation effect.
oolitic limestoneacidizing working fluidpermeabilitywormholesustained releaseeffective acting distance
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