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Study On Fluid-Solid Coupling Numerical Simulation Of Hydraulic Fracturing Extension

Posted on:2008-06-14Degree:DoctorType:Dissertation
Country:ChinaCandidate:Z L LianFull Text:PDF
GTID:1110360212999128Subject:Solid mechanics
Abstract/Summary:PDF Full Text Request
The present situations and development on hydraulic fracturing technique and its numerical model are briefly reviewed in this thesis. The historyl of resolving coupled pore fluid seepage field and stress field is introduced, and the development of fracture mechanics and the method of resolving fracture propagation are also presented in brief. The methodology of simulating the mechanical behaviors of hydraulic fracturing by finite element method is elucidated in detail. The expression of hydraulic pressure on the fracture face along the fracture length is deduced by basing upon pressure descent distribution function, and the corresponding user subroutines were developed and also embedded into ABAQUS. The complex factors of geology such as in-situ stress distribution, mechanical properties, fracturing fluid properties etc were included in the present model. The process of hydraulic fracturing propagation is simulated, and the influences of geologic parameters such as fracture fluid viscidity, in-situ stress et al. are studied. The computer model of multi-fractures in thin oil layers was set up. The effects of interlayer thickness and fracture number on interference among fractures were simulated, and the method of controlling fractures interference was proposed.Several conclusions are drawn from the simulation results. It is viable to solve problems of hydraulic fracturing propagations in the permeable reservoirs with the finite element analysis software (ABAQUS). The concept of critical width is proposed, the critical width could be used to judge a hydraulic fracture is treated as a porous passage or as a fluid flow fracture passage. The void rate is in proportion to normal stress at the fracture tip, and is in inverse proportion to hydrostatic pressure. The void rate of seepage field is in inverse proportion to hydrostatic pressure. When injecting pressure is constant, the fracture initiation pressure is proportional to the magnitude of minimal horizontal stress, critical stress and initial pore pressure, elastic module, and is independent of fracturing fluid viscosity and maxima! horizontal stress. The fracture length and maximal fracturing width are inversely proportional to the minimal horizontal stress, initial pore pressure and elastic module. Further more they are independent of maximal horizontal stress. The process of hydraulic fracturing may be divided into four stages, namely no growth, quick growth, steady growth and slow growth stages. The more number of fractures is treated, the more severity of fractures interference is exhibited, but the degree of interference isn't increased when fracture number beyond special number. The fractures interference is controllable by changing of perforation diameter, perforation number, and injection flow, thereby the alteration of thin and bad oil layer is achieved. The obtained conclusions are of much significance for the hydraulic fracturing treatment parameters optimization and provide a theory reference for the balance limited-entry fracture treatment.
Keywords/Search Tags:hydraulic fracturing, solid-fluid coupling, perforation, numerical simulation, FEA, thin layer, fractures interference
PDF Full Text Request
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