Acid Job Limit in Proppant-Fractured Formations Across Various Formation Types

Abstract HF-based matrix acid treatments are beneficial in removing fines damage in sandstone formations and restoring productivity. In a proppant-fractured formation, fines dissolution/formation stimulation and proppant embedment/conductivity reduction can become competing factors after multi-cycle HF treatments. Consequently, there could exist an "Acid job limit" beyond which the benefit from additional acid treatments is concealed by conductivity loss caused by a weakened formation rock. This study is aimed at establishing an acid job limit for sandstone formations of varying rock strength/fines migration potential. Current study results with high UCS/low- medium porosity sandstone core were compared with those from intermediate UCS/medium porosity core. While a clear acid-job limit was identified in the previous study, high-UCS core tested herein showed permeability increase from fines dissolution and minimum conductivity-loss from embedment. Using a semi-analytical model, skin value was determined as a function of acid cycles and compared to earlier work. The factors causing the different responses for the two formation types were studied so that acid-job limit predictions can be extrapolated to other formations. Various post-test core analysis methods were used to study the effects of acid jobs on proppant-embedded fracture face. Comparison of these results with those from intermediate UCS/intermediate porosity core support that the higher UCS core from the current study experienced minor changes after 8-acid cycles.