Softening of rocks matrix due to water flood: experimental study

Abstract

Petrophysical properties of carbonate reservoirs are lesspredictable than that of siliciclastic reservoirs. One of themain reasons for this is the physical and chemicalinteractions of carbonate rocks with pore fluids. Suchinteractions can significantly change the elastic propertiesof the rock matrix and grains making the applicability ofGassmann’s fluid substitution procedure debateable. Thisstudy is an attempt to understand the mechanisms of fluidrockinteractions and the influence of these interactions onelastic parameters of carbonates. We performed preciseindentation tests on a Savonnières limestone at a microscalelevel under dry, distilled water, and n-Decane saturatedconditions. Our experiments display softening of the rockmatrix after water saturation. We have found that mainlythe cement is affected by water flooding. We also observeda shear modulus reduction in Savonnières limestone in anexperiment performed at ultrasonic frequencies. One of themost important results obtained in our experimental studyis that the Gassmann fluid substitution theory might notalways be applicable to predict elastic moduli of fluidsaturated limestone.