Abstract

In order to reveal the stress shadow effect and its influencing factors in the processing of segregated fracturing in horizontal wells, this paper provides a novel fracture propagation model to simulate multiple hydraulic fracture propagation from a horizontal wellbore. The model couples fracture deformation with fluid flow in the fractures and the horizontal wellbore, includes frictional pressure drop, perforation limited entry, and flow distribution for each fracture. The finite difference method and the finite element method are respectively adopted to simulate fluid flow in fractures and the rock deformation. Meanwhile, Picard iteration method is used to solve the coupled model. The calculation results show that stress shadow do exist, which affects the deformation and propagation of cracks. Because the internal perforation clusters are strongly compressed by the both lateral cracks, the internal crack growth is restrained and the fracture length and width are both small. The intensity of the stress shadow is closely related to perforating cluster spacing, the elastic modulus of rock and so on. The greater the elastic modulus of rock and the smaller the perforating cluster spacing are, the more obvious the interference between the fractures is. Under the same condition, the stress shadow interference between clusters can be alleviated and the extension of the main fracture can also be promoted by injecting low-viscosity fracturing fluids at large flow rate.

1. INTRODUCTION

Horizontal well staged fracturing is one of the key technologies for the development of shale gas, tight gas and other unconventional reservoirs. Mainly through the applications of the staged perforating technology, low viscosity fracturing fluid and steering materials, multiple branch fractures are induced while the main fracture is propagating, which connects the natural fractures. Hence, complex fracture networks occur, which improve the flow channels and then the ultimate recovery of oil and gas. In recent years, with the continuous improvement of composite bridge plug + multi-cluster perforation staged fracturing process, the scale and number of segments of reservoir reconstruction are increasingly large. However, the existing mine practice shows that the small cluster spacing will lead to a considerable number of clusters that are unable to form an effective crack [1]. The presence of these invalid cracks not only dramatically reduce the efficiency of fracturing, but also result in high operation pressure, sand plugging and other engineering problems, which sometimes can even cause failure of the entire fracturing operation. Currently, the optimization problems of segments within the cluster spacing have been studied by some scholars. But these researches are mainly focused on the relationship between the cluster spacing and the optimization of production capacity.

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