Abstract Acid fracturing also referred to as fracture acidising, is an application of hydraulic fracturing in which fluid is mixed with an acid. Recently, special attention has been paid to carbonaceous shale reservoirs as new unconventional energy resources. In this study, geochemical and hydraulic behaviour of the fracture acidising was investigated through numerical simulations. A geochemical model was constructed based on the rock composition and the simulated initial state of the formation before acid fracturing. Then, changes in the pH versus time in the form of pore volume injected (PVI) was modelled using an explicit finite difference algorithm. For the hydraulic phase, a fractured core sample model was built and calibrated using the experimental results for a carbonate sample with the same characteristics. Then the model was modified for a carbonaceous shale sample, and the results were examined considering influential parameters such as injection rate, acid concentration, and temperature. For fractured samples, lower injection rate decreases the required pore volume injected (PVI). Simulation results also showed that an increase in acid content reduces breakthrough PVI up to a certain acid concentration. The temperature of injected fluid did not affect acidising efficiency to a great extent. Finally, statistical analysis was carried out to amend some implications and indirect measurements for experiments. The results of this benchmark simulation can be used to improve acid fracturing design for field case studies and to optimise effective parameters to enhance the productivity in unconventional carbonaceous shale reservoirs.

中文翻译：

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碳质页岩酸性压裂岩心样品反应流动输运数值模拟

摘要 酸化压裂也称为压裂酸化，是一种将流体与酸混合的水力压裂应用。近年来，作为新的非常规能源，碳质页岩储层受到了特别的关注。在这项研究中，通过数值模拟研究了裂缝酸化的地球化学和水力行为。基于岩石成分和酸性压裂前模拟的地层初始状态构建地球化学模型。然后，使用显式有限差分算法对以注入孔隙体积 (PVI) 形式的 pH 值随时间的变化进行建模。对于水力相，使用具有相同特征的碳酸盐样品的实验结果建立和校准裂缝岩心样品模型。然后针对碳质页岩样品修改模型，并在考虑影响参数（例如注入速率、酸浓度和温度）的情况下检查结果。对于裂缝样品，较低的注入速率会降低所需的注入孔隙体积 (PVI)。模拟结果还表明，酸含量的增加会降低穿透 PVI，直至达到一定的酸浓度。注入流体的温度在很大程度上没有影响酸化效率。最后，进行了统计分析以修正一些对实验的影响和间接测量。该基准模拟的结果可用于改进现场案例研究的酸压裂设计，并优化有效参数以提高非常规碳质页岩储层的产能。