Abstract: Acid etched fracture caused by acid fracturing is the main flow channel for fluid, thus, it is necessary to study the flowing rules of fluid in acid etched fracture. Four governing equations commonly used in fracture flow research and their applied conditions are introduced, among which Navier-Stokes equation is chosen as the governing equation for numerical simulation on acid etched fracture. In order to analyze the behavior of fluid flow through acid etched fractures and high-speed non-Darcy effect on fracture conductivity capacity, two kinds of fractures with different acid etching morphologies are reconstructed to solid models by using reverse engineering techniques, and flow experiments are carried out under different flow rates by using finite element numerical simulation. It indicates that, the acidized surface morphology and contact area of acid etched fracture have a great impact on the flow field distribution. The uniform etching fracture with smooth aperture distribution leads to stable flow pattern and low tortuosity, however, with the presence of obvious boundary layer effect caused by narrow fracture width and wide surface area, high viscous resistance will be generated while flowing. The channeling fracture with rough surface and complex aperture distribution results in unstable flow pattern and high tortuosity, and there is an obvious vortex under high flow rate, hence, increasing the inertial resistance loss. The necking phenomenon in contact area leads to circumfluence, and multiple acceleration-decelerations cause additional pressure loss. Meanwhile, with the increase in simulating flow rate, pressure drop and flow rate will gradually deviate from the linear relationship and present the non-Darcy flow phenomenon. The rougher the fracture surface is, the smaller the critical flow and critical Reynolds number are, the stronger the non-Darcy effect of fluid is under the same flow rate, the faster the conductivity capacity decreases.

Key words: acid etched fracture, numerical simulation, flow field distribution, non-Darcy effect, conductivity capacity