考虑压力溶解的酸压裂缝长期导流能力模拟方法

由于酸压施工的高成本及高风险，在设计阶段需要对酸蚀裂缝导流能力这一影响酸压改造效果的关键参数进行预测。目前关于酸蚀裂缝导流能力预测的研究尚存在一些问题，通常情况未考虑酸蚀裂缝长期导流能力的变化，导致预测的产能与实际产能存在一定差异。基于酸蚀裂缝闭合机理，考虑酸蚀裂缝中粗糙接触面上岩石的溶解、扩散和自由面上的溶解沉淀这3个过程的综合作用，建立了考虑压力溶解作用的酸蚀裂缝长期导流能力预测模型。研究表明，压力溶解作用对于酸蚀裂缝长期导流能力的影响不可忽略；压力溶解过程主要受控于裂缝间的化学势的影响，当体系达到平衡，反应停止；裂缝初始宽度、裂缝间初始接触面积比等因素都会影响压力溶解作用的强弱，裂缝初始宽度越大，裂缝间初始接触面积比越小，压力溶解作用越强，裂缝宽度下降越快。研究成果可以提高酸蚀裂缝导流能力的预测精度，为酸压设计提供可靠的参数，更为准确地描述酸压后产能的递减规律。

A simulation method for the long-term flow conductivity of acid-fracturing-induced fracture considering pressure dissolution

Acid fracturing operation is of high cost and high risk, so in the stage of acid fracturing design, it is necessary to predict the flow conductivity of acid-etched fracture which is the key parameter influencing the stimulation effect of acid fracturing. At present, there are still some problems in the researches on the prediction of the flow conductivity of acid-etched fracture. Generally, the variation of long-term flow conductivity of acid-etched fracture is not taken into consideration, which results in a certain deviation of the predicted productivity from the actual value. In view of the comprehensive effect of three actions in acid-etched fractures (i.e., rock dissolution and diffusion on the rough contact surface of and dissolution precipitation on the free surface), a model for predicting the long-term flow conductivity of acid-etched fracture while considering pressure dissolution was established based on the closure mechanism of acid-etched fracture. It is indicated that the influence of pressure dissolution on the long-term flow conductivity of acid-etched fracture shall not be neglected. Pressure dissolution process is dominated by the chemical potential between fractures. And the reaction stops when the equilibrium is reached. The pressure dissolution is also influenced by initial fracture width, fracture-fracture initial contact area ratio and other factors. The larger the initial fracture width is, the smaller the fracture-fracture initial contact area ratio is, the stronger the pressure dissolution is and the higher the decreasing rate of fracture width is. The research results can increase the prediction precision on the flow conductivity of acid-etched fracture, provide the reliable parameters for acid fracturing design and describe productivity decline laws after acid fracturing more accurately.