The relationship between fluid substitution and porous rock's elastic properties

摘要

Analyzing the effect of fluid substitution in porous rocks on rock's elastic properties is very important for understanding the natural property of rocks, especially for fluid identification and prediction in oilfield reservoir management. In the past, a great deal of literature emphasized on the effect of fluid properties on saturated rock properties in the process of fluid substitution, there are relative a few discussion about the influence of rock properties on fluid substitution. In this paper, based on Gassmann's equations, we presented a formula, which quantifies the variation of bulk modulus corresponding to the variation in fluid modulus. Using this formula, we theoretically analyzed the effect of fluid properties, porosity and rock properties on saturated rock elastic properties during fluid substitution. The theoretical results show that, the effect of the variation of fluid content on ' soft' rocks is stronger than those on ' hard' rocks. The smaller the porosity is, the higher the sensitivity of bulk modulus of saturated rocks to the variation in fluid content is. The formula presented here is significant for both theoretical analysis and laboratory simulation in fluid substitutions.