Numerical analysis for promoting uniform development of simultaneous multiple fracture propagation in horizontal wells
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Copyright 2015, Society of Petroleum Engineers. Multi-stage hydraulic fracturing together with horizontal drilling plays an important role in the economic development of unconventional reservoirs. However, according to field analysis of stimulation effectiveness, only a small percentage of perforation clusters contribute to most of the well production. One reason for this low effectiveness is that multiple fractures do not take the same amount of fluid and proppant due to fracture interaction (i.e., stress shadow effects). Unfortunately, how best to minimize the negative effects of stress shadowing is still poorly understood in the petroleum industry. In this paper, we analyzed this problem in order to promote more uniform fracture growth using our complex hydraulic fracture development model. We employed our fracture propagation model that couples rock deformation and fluid flow in the fracture and horizontal wellbore. Partitioning of flow rate between multiple fractures was calculated by analogizing to the electric circuit network. Fracture development is dominated by flow rate distribution, which is controlled by flow resistance within the fractures. For simultaneous multiple fracture propagation, non-uniform flow rate distribution is induced because stress shadow effects exert additional flow resistance on the interior fractures. To balance the extra resistance introduced by the effects, we investigated two adjustment approaches to promote uniform fracture development. The first approach was to adjust perforation number or diameter to increase flow resistance entering the exterior fractures. The second was to mitigate stress shadow effects through managing non-uniform fracture spacing. We found that decreasing perforation diameter or numbers of the exterior fractures can divert fluid into the interior fractures and promote even fracture growth. Stress shadow effects can be mitigated by moving the two interior fractures away from each other and toward the exterior fractures. The key mechanism is to maintain even flow resistance within each fracture and facilitate fractures to obtain the same amount of injection fluid. Furthermore, flow resistance is affected by near-wellbore fracture tortuosity, natural fractures, and stress heterogeneity in the reservoirs. These factors might also be effectively controlled by adding extra flow resistance to pass perforations, provided that this extra resistance is larger than the extra resistance introduced by the factors. This work analyzes the problem of uneven development of multiple fractures along the horizontal wellbore and provides new insights into how to control simultaneous multiple fracture propagation. It offers potential approaches for engineers to apply in the field to optimize hydraulic fracturing treatment design and thereby maximize well production cost-effectively.
