(713b) Enhancing Hydraulic Fracturing Productivity Via Model-Based Feedback Control
Motivated by these considerations, we focus on the development of a model predictive control framework for the design of pumping schedule to regulate the spatial variation of proppant concentration across the fracture at the end of pumping for conventional and unconventional reservoirs. In conventional oil reservoirs, high-viscosity fracturing fluids ensure that most of the proppant remains in suspension during the treatment and the closure process. Thus, it is sufficient to regulate the suspended proppant concentration along the fracture at the end of pumping. In unconventional reservoirs, however, predominantly low-viscosity (âslick-waterâ) fluids are used and the proppant settles quickly forming a proppant bank, which will continue to grow until it reaches the equilibrium height; a state when the rate of proppant washout on top of proppant banks due to the shear force is equal to the rate of bank formation via proppant settling. To this end, we initially focus on the development of a first-principle model of a hydraulic fracturing process to obtain fundamental understanding of the proppant bank formation mechanism and its relationship to manipulated input variables such as proppant concentration and flow rate of the injected fracturing fluids. The optimal fracture geometry is obtained by applying Unified Fracture Design for conventional reservoirs  and a section-based optimization method for unconventional reservoirs . Next, high-fidelity simulation data has been used to construct a data-based linear approximate model to design a Kalman filter that estimates unmeasurable states. Lastly, a model-based feedback controller is developed to achieve the uniform proppant bank height and suspended proppant concentration along the fracture at the end of pumping for conventional and unconventional reservoirs by explicitly taking into account the desired fracture geometry, type of the fracturing fluid injected, total amount of injected proppant, actuator limitations, and safety considerations.
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