Effect of Nonreactive Minerals on Acid-Etching Hydraulic Fracture Behavior and Conductivity in Carbonate Rocks

Summary Nonreactive minerals, such as quartz and talc, are frequently observed in carbonate reservoirs due to the sedimentary environment and geological processes. However, scant attention has been given by scholars to the impact of these nonreactive minerals on acid-etched fracture morphology and conductivity during acid fracturing. To clarify the acid flow and reaction behavior in carbonate rock composed of complex minerals, a mineral characterization model simultaneous for calcite, dolomite, and nonreactive minerals is first developed in this paper. Then, combined with the thermal-hydraulic-chemical coupling acid-etching model, it can study the impact of mineral content and distribution on the acid-etching fracture behavior. In addition, the acid-etching model is validated by acid-etching laboratory experiments, and the acid-fracture conductivity model is also established by testing the conductivity of rock slabs with different mineral compositions. Based on the new model, the effects of different mineral compositions on the acid flow behavior, effective acid penetration distance (EAPD), and conductivity were investigated. The research results show that the mechanism of nonreactive mineral to increase EAPD depends on the initial hydraulic fracture width, mineral distribution, and content. The acid concentration profile along the fracture length has the feature of segmentation when the circumferential flow phenomenon occurs. With the increase of the nonreactive mineral content, the EAPD increasing rate in the calcite-nonreactive mineral interaction distribution formation is faster than that in calcite-dolomite. The impact of the nonreactive mineral on conductivity is large in limestone but can be ignored in dolomite. These findings can provide guidance for the design of acid fracturing in such siliceous carbonate reservoirs.