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.