Conductivity Prediction Based on Fracture Closure Theory and 3D Printing

The conductivity of acid-etched fractures is important to the optimization of acid-fracturing program and the production evaluation of a well. In testing the conductivity of acid-etched fractures, the core column under test may break down at high closure pressures and this will cause the test results to become inaccurate. To deal with this problem, the conductivity of acid-etched fractures is studied using the 3D scanning and 3D printing technologies as well as the theory on the closure of fractures under pressure. In the study, the core samples were first acid etched. Using reverse modeling technology, the 3D model of the acid-etched cores was obtained. Using the SLA3D printing technology, a 3D core model with rough walls was prepared. Then seepage experiment was conducted under different confining pressures on the acid-etched cores and the 3D printed cores. Using the discretized data processing method, the deformation of the fractures under the action of the closure stress was presented using numerical simulation in combination with the Hertz contact model and a conductivity prediction interface programed with the N-K model. The study results show that the 3D digital model of the real rocks and the real core samples made with the SLA3D printing technology together can be an effective way of preparing complex fractured core models. The errors of the conductivity test made on the acid-etched cores and the 3D printed cores, the test made on the 3D printed cores as well as the numerical simulation are all less than 7.7%, and the errors between the numerical simulation results and the carbonate core test results are less than 9.6%. The experiment and numerical simulation results obtained under low closure pressures can be used to predict the conductivity of the fractures under high closure pressures. The study method proposed provides a reliable approach for quantitatively characterizing the conductivity of acid-etched fractures.