Numerical Simulation Of Integral Hydraulic Fracturing With Coupling Between Fluid And Rock

Hydraulic fracturing as a positive stimulation treatment in reservoirs has been widely used in low permeability reservoirs. In 1990's, it has been put forward that hydraulic fracturing must be combined with reservoir engineering to meet the development requirement of low permeability reservoirs.The reservoir survey and experimental study show that many reservoirs, especially low permeability reservoirs or ultra low permeability reservoirs are sensitive to the variation of formation pressure. As a matter of fact, the fluid flowing though porous medium is intensively influenced by the coupling of formation fluid and rock elastic-plastic deformation. However, rock and fluid are considered as two independent systems, and the coupling effect has not considered in individual well's fracturing or integral fracturing. In this thesis, coupling theory was introduced into the hydraulic fracturing field, and numerical simulation of integral fracturing with coupling was researched.(1) The characters of rock mechanics in SHA-3 payzone have been tested by tri-axial instrument; the elastic modulus and Poisson's ratio were obtained. This work laid a foundation for the integral fracturing with coupling.(2) According to definition of porosity and permeability, effect of rock deformation on porosity and permeability were considered. And the model of strain porosity and strain permeability were established, the effect of formation pressure on porosity and permeability could be simulated.(3) Based on Darcy's law and material balance principle, mathematical model of three-dimensional three-phase was derived in porous medium with artificial fractures, and the gravity was considered in the model. Then, model of the strain porosity and strain permeability was combined, and the mathematical model of integral fracturing with coupling was established.(4) According to the finite element theory, numerical formula of finite element analysis of the integral fracturing model with coupling was given, and a simulator was developed. This work improved the previous calculation, which used finite difference in fluid flow and finite element in rock deformation.(5) The case studying the thesis proven the correction and validation of the theoretical modeling and simulator. The coupling between rock and fluid on production are strong, especially in the stress sensitive reservoirs.(6) The simulator can be used to predict the productivity performance in homogeneous and non-homogeneous reservoir, single fracturing and/or integral fracturing, two-phase or three-phase flow. Moreover, it can simulate the production performance in well group and block with different fracture lengths and different fracture conductivities. The simulator is an effective tool for integral fracturing project.