A NUMERICAL INVESTIGATION OF PULSE HYDRAULIC FRACTURING TREATMENTS USING THE X-FEM TECHNIQUE

Traditional hydraulic fracturing (THF) treatments suffer difficulties such as high injection pressure, poor controllability, and local stress concentration. In many cases, THF leads to the activation of a relatively small number of perforations with limited contribution to the enhancement of the overall permeability of the reservoir. Alternatively, pulse water pressure may be exerted inside the borehole as a remedy to produce multiple macroscopic main cracks along the borehole axial and radial directions. To reach a better understanding of this technique so as to improve its efficiency in practice, the role of the contributing elements, namely, the fracturing fluid mean pressure, its amplitude, and its frequency, needs to be investigated in conjunction with the properties of the bulk. In this paper, an extended finite element framework is developed to study pulse hydraulic fracturing (PHF) within a tight-low permeability reservoir. To this end, the momentum balance equation of the medium is solved in conjunction with the flow continuity equations of the fracturing fluid using the staggered Newton algorithm. In the context of X-FEM, the displacement field is enhanced using the Heaviside enrichment function to account for the discontinuities due to cracks in the body. The hydrofracture inflow is modeled for both the laminar and turbulent flow regimes. The nonlinearities within the hydrofracture tip are taken into account using the potential-based cohesive zone model, where the crack growth direction and increment are determined by taking advantage of the energy-based cohesive stress functions. Using the developed computational framework, the performance of PHF treatments is investigated through various numerical simulations.