Analyses of Processes, Mechanisms, and Preventive Measures of Shale-Gas Reservoir Fluid, Completion, and Formation Damage

Abstract

A comprehensive review and modeling of the natural and induced formation damage processes and their governing mechanisms involving the various aspects of gas-bearing shale reservoir formations is presented. The investigation and modeling efforts are carried out in several steps. First, the damage potential of shale formations containing large quantities of clay and nonclay inorganic, and organic materials, and natural fractures filled with cement and other debris is delineated. Second, the thermal, chemical, and stress interactions between the drilling and fracturing fluids of frequently used types are described. The various relevant processes and their fundamental mechanisms, including under/over balanced drilling, fracturing fluid disposition and retainment, wettability and nonequilibrium fluid transmission and spontaneous imbibition, swelling and fluidization, gas blockage occurring in extremely-low permeability shale porous media, are reviewed. These processes are described by phenomenological rate processes and the resulting modeling equations are solved simultaneously by a finite-difference-based numerical method. A number of representative case studies are considered and solved numerically. The results provide valuable insights into the nature of the shale-gas reservoir formation damage, indicating the significant roles of the different orders of magnitude rate processes and the thermal, chemical, and stress shocks causing formations damage during drilling, completion, and production. It is demonstrated by various numerical results that we can take advantage of the significant differences between the rates of occurrence of the adverse processes to effectively control, minimize, and/or prevent the shale-gas reservoir formation damage. This provides a scientifically-guided protocol for mitigation of gas-bearing shale formation damage.