The purpose of designing an acid fracturing model is to examine the two factors that measure the effectiveness of the acid fracturing treatment. The two factors are the acid penetration distance and the fracture conductivity after closure stress is reached.
The acid fracturing model is designed by coupling a fracture propagation model and an acid transport model. The advanced fracture propagation models are developed numerically by the finite element method (FEM,) or the extended finite element method (XFEM.) However, the acid transport models that are reported in the literature are developed using the finite difference method (FDM.) The finite element method is a more stable and accurate technique to model the complex system of the acid transport along with fracture mechanics and heat transfer than FDM. Furthermore, FEM is a more powerful and suitable technique for meshing sophisticated geometries such as fractures. Thus, an acid transport model has been developed numerically using FEM.
The objective of developing this FEM model is to eliminate the need of using different mapping and coordinate transformation techniques for the fracture propagation model and the acid transport model; hence, diminishing the inaccuracy when meshing the geometry.
The developed FEM model has been validated against analytical and numerical models, and it has been verified that the algorithm is stable and robust. The developed model predicts accurate velocity and temperature profiles. In addition, the model can handle acids with non-Newtonian flow behavior at a specific acid viscosity and acid dissolving power. It has been found that acids with shear thinning flow behavior yields shorter acid penetration distance compared to acids that are behaving as a Newtonian fluid. Furthermore, the effect of wormholes on the acid distribution has been studied, and it has been found that high injection rates result in deeper wormholes.
The assessment of geomechanical properties of unconventional reservoirs is significant as they assist in placement as well as understanding of the geometry and properties of multi-stage hydraulic fractures in horizontal wells. Severe heterogeneities at micro-scale in addition to possibility of having non-intact samples provide opportunities for using micro-mechanics techniques on drill cutting size samples. This will lead to not only have a continuous log of geomechanical properties on heterogeneous formations but also be able to measure the mechanical properties of non-intact samples accurately. This study presents a multi-scale comparison of the elastic properties such as Young’s modulus and Poisson’s ratio on the Eagle Ford Formation. Peak Force Quantitative Nano-mechanical (PF-QNM) AFM-based technique has been performed and compared with true triaxial testing. A new model for AFM evaluation that corrects Young’s modulus in dependency of Poisson’s ratio has been developed. The results indicate that the distribution of Young’s modulus is separated into two regions, one dominated by brittle minerals indicating higher values and one dominated by ductile rock components resulting in lower values. The findings are significant as PF-QNM testing can be performed where only drill cutting-size samples are available, as it shows strong agreement with the triaxial testing result.
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