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Abstract Based on the coupling theory of fluid seepage and rock stress-strain in porous media，the numerical calculation equation for rock breakdown pressure during hydraulic fracturing process is deduced，and a new calculation method is proposed. The method considers fully the coupling effect of rock deformation and fluid seepage. Numerical calculation technique of finite element method is used，and it can simulate the distribution of effective stress around well bore with time and space under injection of fluid into the formation. Therefore，not only rock breakdown pressure can be calculated，but also rock breakdown time can be obtained. The theory of breakdown pressure numerical calculation overcomes many disadvantages of conventional analytic calculation method on breakdown pressure. For example，conventional analytic calculation method can¢t calculate accurately the breakdown pressure for the rise of fluid pressure which leads to aggravation of stress around well bore，exact rock breakdown time，and so on. The buildup of the calculation theory realizes breakthrough of numerical calculation of rock breakdown pressure and improvement of calculation accuracy，and a new theory and method are found for rock breakdown pressure of fracturing process.
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Received: 24 October 2008
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