Experimental and Numerical Evaluation of Acidizing Effect Duration for Diverting Acids in Reservoirs

Acidizing is one of the most economical and effective methods for ensuring the continuous and stable production of an oilfield and improving oil recovery. Diverting acids are more and more widely used in oilfields. However, it is difficult to accurately determine such parameters as acid discharge, concentration, and acid-rock reaction duration before construction, which may result in poor acidizing effect and low economic benefits. In this paper, the viscosity of diverting acid, reaction kinetics of acid rock, and residual acid limit are experimentally determined as well as numerically simulated using pressure, temperature, seepage, and geological models via the MATLAB software. The relationship between diverting time and peak viscosity time of diverting acid (DA) is studied and analyzed. For formation temperatures below the DA gel-breaking temperature, the DA with large displacement and low acid concentration should be selected. For formation temperatures close to the gel-breaking temperature, a medium acid concentration with large discharge rate should be selected. For a formation temperature exceeding the gel-breaking temperature, DA with high acid concentrations and small discharge rate should be selected. When the formation temperature is lower or close to the acid gel-breaking temperature, the acidizing effect of DA can be improved by adjusting the amount of injected acid. When the formation temperature is higher than the acid gel-breaking temperature, high-temperature corrosion inhibitors and adsorbent should be added in order to reduce the acid-rock reaction rate and improve the acidizing effect. The research results are of great significance in field acidizing construction.