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Abstract Oil/gas produced from reservoir formation will inevitably change its pore pressure，and then affect its rock mechanical properties. Strength properties of rock under different pore pressures and deformation properties of rock under periodic pore pressure are studied by triaxial compression tests in this paper. The results show that when confining pressure keeps constant，triaxial compressive strength，elastic modulus，volumetric modulus and shear modulus all present increasing trend with the decrease of pore pressure，while the Poisson ratio presents total decreasing trend. For the reservoir developed by blowdown recovery，with the decrease of pore pressure，volumetric modulus increases and volumetric compressibility decreases，rock compressibility gradually weakens. During the periodic loading and unloading process of pore pressure，axial strain，radial strain and volumetric strain will all gradually accumulate with the loop cycle，and change greatly in the initial loading and unloading，gradually tend to be stable with the increasing cycle numbers. The variation in rock strength and deformation with pore pressure shows that the drop of pressure in the early development of the reservoir has a serious impact and injury to the reservoir properties. If effective measures are never taken to stabilize the formation pressure in the early，substituted by injecting fluid in the later reservoir development period to change the formation permeability，it won?t take apparent effect. Moreover，the grand total of rock deformation may induce formation damage and even catastrophic events.
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Received: 01 July 2010
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2011, Vol. 30 
