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Abstract Quantitative studies of pore fluid influence on the mechanical properties of rocks are carried out on mesoscopic scale. The nonlinear strain is decomposed into a classical part and a nonclassical contribution which is described by nonclassical elastic units(NCU). Based on the analysis of the mechanism on mesoscopic scale，fluid influences on rock mechanical behavior and stiffness under various saturations are discussed. Introducing new forms of macroscopic solid-fluid interaction functions，Preisach-Mayergoyz(PM) space under different saturations are obtained from the inversion of experimental data；and the influences of fluid saturation on PM space density are investigated. The entire variation between Young¢s modulus and compressional wave velocity with saturation is studied. When saturation increases from 0% to 20%，the dynamic modulus decreases for classical part，and the PM space density increases for nonclassical part，respectively. Whereas saturation is between 20% and 80%，the dynamic modulus and PM space density barely changes. As saturation increases from 80% to 100%，the dynamic modulus increases and the PM space density decreases，contrary to the low saturation condition. The classical and nonclassical nonlinear strains of saturated rocks are obviously larger than those of dry rocks in accord with the PM space density distribution. These numerical results are generally consistent with the experimental results. This simulation research has potential prospects for the problems such as reservoir prediction and description，safety of constructions near slope area，nuclear storehouse properties，geophysical inversion，and data interpretations.
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Received: 23 March 2009
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