Characterization of Geomechanical Poroelastic Parameters in Tight Rocks

Abstract

In petroleum engineering and geophysics, it is often assumed that the rocks are completely rigid bodies with a totally interconnected pore space and that the fluid within the pores does not affect and are independent of the strains in the porous media. These assumptions are often not accurate and also unrealistic because the pore pressure effects are of great importance in all of the geomechanical processes occurring in the subsurface. The hydraulic and mechanical processes are coupled so that the rock deformation causes pore pressure changes and fluid flow (displacement relative to the solid). The time- dependent coupling of the hydraulic and mechanical processes can be described by the theory of poroelasticity. Application of this theory requires the availability of material parameters through experiments. In this work, the main poroelastic parameters are determined for some rock types of interest. The focus of this work is concentrated in low porosity rocks that are commonly encountered. Experimental procedures under drained, undrained and unjacketed conditions were initially completed in Berea Sandstone. Then, Indiana Limestone, Westerly Granite and Welded Tuff specimens were tested in order to obtain Skempton?s pore pressure parameter B, Biot?s coefficient of effective stress ?, Bulk Modulus and Grain compressibility. Preliminary results suggest that the parameters B, K and ? will change in accordance to the permeability and the porosity of the rock, while K_(S) would depend more on the mineralogy and deposition characteristics of the rock.