Abstract
Simultaneous multiple-fracture treatments in horizontal wellbores have become one of the key methods for economically and efficiently developing oil and gas resources in unconventional reservoirs. However, field data show that some perforation clusters have difficulty propagating fractures due to the internal mechanism of competing initiation and propagation among the fractures. In this paper, the physical mechanisms that influence simultaneous multiple-fracture initiation and propagation are investigated, and the effects of engineering parameters and in situ conditions on the nonuniform development of multiple fractures are discussed. A 3D fracture propagation model was established with ABAQUS to show the influence of the stress shadow effects and dynamic partitioning of the flow rate by simulating the propagation of multiple competing fractures generated in the perforation clusters. Based on the results of these simulations, simultaneous flow in multiple fractures can propagate evenly. Through adjusting the number of perforations in each cluster or the perforation diameter, the effect of the stress shadow can be significantly reduced by increasing the perforation friction, and the factors that affect the development of multiple fractures are changed, from the stress shadow effect to the dynamic partitioning of the flow rate. When the stress shadow effect is dominant, increasing the fracturing fluid viscosity promotes the uniform development of multiple fractures and increases the fracture width. When the dynamic partitioning of the flow rate is dominant, increasing the injection rate greatly affects the uniform development of multiple fractures.
Highlights
The hydraulic fracturing technique is a widely used wellstimulation technique to effectively and economically develop oil and gas resources in low-permeability unconventional reservoirs [1, 2]
The advantage of multicluster fracturing over conventional hydraulic fracturing is that it allows multiple perforation clusters within a single stage to form several hydraulic fractures simultaneously through a single pump, resulting in multiple fracture surfaces after fracturing fluid is pumped into the reservoir, achieving a larger effective reservoir volume
The results showed that the dynamic partitioning of the flow rate has an important influence on the uniform propagation of multiple competing fractures
Summary
The hydraulic fracturing technique is a widely used wellstimulation technique to effectively and economically develop oil and gas resources in low-permeability unconventional reservoirs [1, 2]. Numerical simulation methods can better represent the reservoir in situ conditions and the nonlinear dynamic boundary problem, which is influenced by many factors, such as the Young modulus of the target layer, fracturing fluid viscosity, and pump rate [13]. Scholars found that perforation-cluster spacing, fracture height, target formation thickness, and pumping rate had significant influence on the simultaneous propagation of multiple fractures in a horizontal well [17]. From the numerical simulation analysis, through a reasonable design, such as the reasonable perforation cluster spacing, the injection rate, and the fracturing fluid viscosity, the adverse effects of the stress shadow can be controlled. The influence of fracturing fluid viscosity, injection rate, and perforation friction on the uniform development of multiple fractures is analysed comprehensively by using this model, and some suggestions to promote uniform multiplefracture growth are proposed
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