A shale fracture network fracturing perforation cluster spacing optimization method and system

Abstract

The invention provides a method and system for optimizing spacing of shale fracture network perforation clusters. The method and system analyze and solve changes of induced stress during full three-dimensional expansion of multiple fractures in the case of multiple perforation clusters by employing finite element numerical simulation, local maximum and minium horizontal main stress difference around fractures is eliminated by using inter-fracture stress interference, local horizontal main stress of a stratum is approximately isotropic, a local optimum stress field is formed, main facture diverting and natural fracture opening are promoted, and a network of fractures is thus formed.

Description

technical field [0001] The invention relates to unconventional oil and gas reservoir transformation technologies such as shale gas and tight sandstone gas in the field of oil and gas field development, and in particular to a method and system for optimizing the spacing between perforation clusters in shale fracture network fracturing. Background technique [0002] Different from conventional oil and gas reservoirs, unconventional oil and gas reservoirs such as shale often need to form a fracture network and implement network fracturing technology when undergoing staged fracturing. To achieve this purpose, multiple clusters of perforations are often used in each fracturing stage to form complex fracture propagation. Since the opening of fractures and the change of fluid pressure in the fractures will affect the mechanical properties of the formation, and induce stress in a certain area around the fractures, there will be stress interference among multiple main fractures. Rea...

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Problems solved by technology

It can be known from the prior art that the influence of induced stress on the propagation of network fractures is mainly reflected in two aspects: (1) When iterating the fracture pressure and fracture width, the original stress at each fracture unit needs to be added with stress Influence the induced normal stress, which in turn will affect the fracture internal pressure and fracture width, leading to changes in the fracture propagation form; (2) When considering the induced stress, the in-situ stress at the front of the fracture propagation will change, and the local principal stress will occur Inversion, causing the fracture to turn, and then affecting the shape of the fracture network

At present, most of the mechanism studies on this aspect are: (1) The fracture shape is set in advance, assuming the fracture geometry (length, width, height), and the solution is solved by establishing the stress interference analytical equation, which cannot truly simulate the full three-dimensional expansion process of the fracture. Influence of rock deformation and pore pressure change on the stress field; (2) Based on the homogeneous and isotropic two-dimensional plane strain model, it is assumed that the rock is completely elastically deformed, rock plasticity is not considered, and the fracture height correction factor is used instead seam height

These traditional analysis methods have limited ability to describe the variation law of multi-fracture propagation ground stress, and have not optimized the spacing of perforation clusters, so the effect of practical application is not very ideal

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