RESEARCH ON VARIATION OF VELOCITY SENSITIVITY AND WATER SENSITIVITY BEFORE AND AFTER ACID ETCHING IN CARBONATE RESERVOIR

Most of the carbonate reservoirs need acidization or acid fracturing, so it is important to research the samples′ fluid sensitivity after acid etching. In the past, the main research was on stress sensitivity and alkali sensitivity or conventional fluid sensitivity, the fluid sensitivity of the samples after acid etching has never been researched. In this paper, a typical carbonate reservoir in Sichuan basin was selected and the experiments of velocity sensitivity water sensitivity before and after acid etching were compared. Results show that the valuation of damage degree of conventional velocity sensitivity is weak to moderate, after acid etching it is moderate to strong. The degree of water sensitivity has the tendency to strengthen after acid etching. The core matrix becomes loosely, and the particles in the fractures are easy to shatter and migrate after acid etching. The main reasons of the water sensitivity′s strengthening after acid etching are the diffusion migration of illite and chlorite, and hydration expansion, dissolution- precipitation of anhydrite. The enhancement of the sensitivity of carbonate reservoir during acidization and acid fracturing should be valued and the experiment evaluation should be strengthened.