Our work shows that the most important single consideration in hydraulic fracturing should be downward convection of heavier proppant-laden stages in vertically uncontained fractures. This mechanism has been absent in simulators and design approaches used by the industry: some industry personnel still refuse to accept the negative implications of extensive vertical fracture growth and, even when accepted, the convection process cannot be handled by current industry models, The efforts reported here are aimed at quantifying the phenomenology involved and incorporating the results into a practical simulator, developed for the Gas Research Institute (GRI), which also uniquely represents the physics of 3-D rock deformation and fluid flow. Two major conclusions should greatly affect field practice:1. Convective downward motion, even in simple fluid treatments, dominates over particle settling.
Encapsulation of viscous fluids by low-viscosity fluidsavailable (e.g. gashater) greatly accelerates the process.Our quantification covers a range of fluids and fracture opening behavior, for both laboratory conditions (as verification) and for typical field job schedules. Super-computer simulations were required for detailed analysis of the processes involved, but the experience gained is being down-loaded to a simpler practical fracture analysis system, which was adapted to run on portable (PC) machines, for on-site implementation and re-design of treatments, based on real-time analysis of data collected. Such simulations show that convection should be the dominant mechanism in fracturing of most reservoirs and this leads to a series of practical recommendations which are greatly at odds with "conventional wisdom" in the industry, with resulting major implications for the execution, cost-savings and benefits of fracturing.
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