A Laboratory Evaluation of Acid Propagation in Relation to Acid Fracturing: Results and Interpretation

Abstract

ABSTRACT To design acid fracturing treatments, acid fracturing models require acid leakoff values including experimental coefficients such as acid propagation rate and acid penetration distance into the formation. This paper presents an experimental study aiming at defining a methodology for the acquisition of these parameters. The pressure variation curve obtained during a conventional acid injection experiment in a Hassler cell is analysed in relation with the dissolution mechanism. X Ray Computerized Tomography is applied to characterize the dissolution patterns. Influence of core length, acid concentration and acid flow rate are considered. Critical values are found above which the filtration process is dominated by the wormholing mechanism. Critical lengths and rates are interpreted in terms of the Damkohler Number, i.e. the ratio of the acid brought by transport to the acid consummed by the chemical reaction. In addition, from the interpretation of the experimental results, a new methodology is proposed for the measurement of acid propagation rates and distances.