ABSTRACT

With the great success of the Barnett shale gas play and the discovery of immense global reserves of this cleaner energy source, shale gas development has become a major topic for energy companies and governmental organizations alike. However, shale gas development remains economically challenged due to significant development issues such as proper resource and reservoir characterization, optimized completion design, and accurate estimation of both production performance and total recovery. These challenges are often related to the extreme heterogeneity and complexity of fractured or bedded shale gas formations. Due to the often nanodarcy permeability of the shales, multi-stage hydraulic fracturing (HF) stimulation is typically required to make shale gas wells economic. However, billions of dollars are spent every year on HF completions using, essentially, a trial-and-error design process and/or by looking at completion and production trends from data mining efforts. This occurs because the conventional HF design tools, most based upon simple two-dimensional analytical solutions developed more than 40 years ago, simply lack the proper physics required to understand the hydro-thermo-mechanical processes involved in the propagation of a hydraulic fracture in a naturally fractured rock mass. Many rules-of-thumb and empirical solutions are being developed to address the limitations of the common design tools, but the predictive capacity of these models for new plays and new geological/ petrophysical conditions is, at best, very limited. Emerging numerical techniques are available that can address hydraulic fracturing in naturally fractured formations, like shale gas, and that are based upon the proper, 'first physics' of the mechanical and flow behavior of fractured formations. These techniques will allow the industry to gain greater insight and understanding of how natural fracture geometry and intensity, fracture hydro-mechanical properties, and stress field affect HF performance in the presence of different operational parameters such as perforation cluster spacing, injection rate and pressure, fluid viscosity, and stage volume. Furthermore, these numerical techniques can also provide a means to directly evaluate microseismicity, which offers a powerful tool to validate the HF designs and lead to better predictive tools for HF optimization.