Optimum Acid-Fracturing Treatments for Ultradeep Limy Dolomite Reservoirs Based on Conductivity Tests

Acid-fracture conductivity has a major impact on acid-fracturing effects. In this paper, influences of acid concentration, temperature, and closure-stress loading time on conductivity under different acid-fluid systems have been researched based on experimental analysis for deep limy dolomite reservoirs. The measured conductivity showed high correlation and specific changing patterns with the above factors. Quantified relationships and equations between the conductivity and these factors were suggested in this paper. Additionally, a strong acid-etching effect caused by crosslinked acid and diverting acid has been observed during the tests. This could lead to high conductivity as well as broken rocks due to pressing with high-concentration acid. In this study, a 50-hour long-term conductivity test has been designed under the closure stress of 60 MPa which was closest to the actual reservoir conditions. The results showed that conductivity retention rate for each test group is less than 40%. By establishing assessment criteria of long-term and short-term conductivity based on the conductivity retention rate, linear relationships with high correlation and quantified equations of the conductivity retention rate in the same acid-rock reaction system could be obtained.