Investigation On The Law Of Multifracture Propagation And Fracture Network Extension Of Horizontal Wells In Shale Gas Reservoir

Shale gas reservoirs usually have the characteristics of low porosity,low permeability,and strong heterogeneity.Compared with conventional reservoirs,mining is difficult.In most cases,large scale fracturing is needed to achieve economic exploitation.Multi-stage horizontal fracturing technology is the key technology for largescale economic exploitation of shale gas.Some fracturing fractures have no contribution to production.On the one hand,due to the existence of stress interference between fractures,some fractures are not fully developed and failed to form effective fractures.On the other hand,there may be no complex fracture network in the fracturing process.Based on this,in order to improve the fracturing reconstruction effect of shale gas reservoir,in this paper,the synchronous expansion of multiple fractures and the extension of fracture network are studied.First,based on the ABAQUS finite element platform,a three-dimensional multi cluster hydraulic fracture propagation model is established.The model can take account of the stress interference between the fractures and realize the automatic distribution of the flow.The model is used to simulate the synchronous expansion process of the three clusters of hydraulic fractures in a fracturing section.This model is used to analyze the influence of geological factors and construction factors on the propagation of multi cluster fractures.It is found that cluster spacing has an important effect on the uniform expansion of multi cluster fractures.With the increases of elasticity modulus,the area of intermediate cracks increases,and the total crack area increases as well.With the increase of cluster spacing,multiple cracks can achieve uniform expansion.High viscosity fracturing fluid can promote the relatively uniform expansion of multi fractures.When the total amount of injected fracturing fluid is constant,with the increase of displacement,the propagation of multiple cracks is relatively uniform,which helps to improve the total area of cracks.Then,a fracture network extension model based on the inserting global cohesive element is established.The influence of formation factors and construction factors on the fracture network extension in the fractured formation is studied.It is found that when the horizontal stress difference is small,hydraulic fractures have no preferential extension direction,and tend to expand along natural fractures,which can activate more natural fractures and form more complex fracture networks.When the horizontal stress difference exceeds 5MPa,hydraulic fractures tend to expand along the direction of the maximum horizontal principal stress,the number of activated natural fractures is reduced and the fracture network becomes single.The injection rate of fracturing fluid has a significant effect on the fracture network morphology.With the increase of the injection rate of fracturing fluid,the fracture network morphology tends to be complex.In this model,the viscosity of fracturing fluid has little effect on the fracture network shape.With the increase of viscosity of fracturing fluid,the number of activated natural fractures is reduced,and the fracture network morphology tends to be simple.With the increase of natural fracture cementation strength,the number of natural fractures activated by hydraulic fractures decreases,and the fracture network tends to be simple.When the spacing is small,due to the mutual interference between the main fractures,the expansion of the middle fractures is inhibited,and the number of activated natural fractures is also less.With the increase of the crack spacing,the stress interference effect between the cracks is weakened,the three cracks are fully expanded,the number of activated natural fractures increases,and the fracture network becomes more complex.The research results can provide theoretical guidance for the design and optimization of high efficiency fracturing construction of shale gas.