Acid fracturing stimulation involves several major steps; a hydraulically induced fracture is created by pad fluids first, then reactive fluids are injected into the fracture, often alternating with a viscous pad to create etched fracture length. When pumping stops, the fracture closes up, and conductivity is created by an uneven fracture surface. An integrated modeling approach is introduced to simulate acid fracturing processes and diagnose operation problems. The integrated design/diagnose approach includes a fracture propagation model for fracture geometry, an acid transport model and a well performance model. The fracture geometry model is coupled with a 3D acid fracturing model to simulate acid transport and the resultant fracture conductivity. The fracture conductivity is then utilized in the well performance model to predict the well productivityafter treatment. This simulated well performance can be used to match the production data to verify the models. In this field case study, we did not have the information about formation leakoff to start the fracture geometry model. To successfully analyze the well treatment, a three step inversion workflow was proposed. The inversion workflow started from estimating a skin factor after stimulation by matching the production data. This skin factor was then converted to a fracture length that resulted in the production history. A pseudo 3D fracture model was used to predict fracture geometry. With the fixed length as a constraint, we varied the leakoff coefficient until we obtained the correct geometry. The simulated fracture geometry from the fracture propagation model was used as an input in the 3D acid fracturing model to simulate the fracture conductivity profile. The conductivity was confirmed with the fracture conductivity from lab experimental test result. To close the analysis loop, the conductivity should also be consistent with the one used in production history matching.
Fracture geometry was generated by the commercial software, MFrac, and acid fracturing was simulated by a 3D model developed before. Two wells are selected for the field case study to illustrate the application of the approach, with one well has improved productivity after acid fracturing, and the other has no response after acid fracturing. By applying the inversed integrated 3D acid fracturing modeling workflow, it showed that the well with high productivity had a fracture conductivity resembling the conductivity values fromthe experimental lab measurements. The well with low productivity showed poor fracture length and width, leading to a low production.