1 Acoustic Signatures of Patchy Saturation

  • Published 2001

Abstract

We consider two saturation patterns in a partially saturated geomaterial. The first is the homogeneous pattern where saturation is the same at the pore scale at any location in the rock. The second is the patchy pattern where a large fully-saturated patch is surrounded by a dry region. In both cases the global saturation in a large volume of the rock is the same. At the same global saturation, the effective acoustic properties of the rock vary depending on the saturation pattern. We offer a practical method for identifying the dominating saturation pattern from dynamic Poisson's ratio obtained from sonic well-log measurements. This method performs well in soft rocks whose acoustic properties are most sensitive to the way fluid is distributed in the pore space. INTRODUCTION AND PROBLEM FORMULATION The heterogeneous nature of porous rocks and soils often results in the heterogeneity of fluid distribution on scales greater than pore or grain size. In a partially saturated rock two end members of pore fluid arrangement may exist: (a) the fluid is evenly distributed within the pore space, i.e., fluid distribution is homogeneous; and (b) the fluid is arranged in fully saturated patches that are surrounded by dry or partially saturated regions, so that fluid distribution is patchy. These patches may include thousands of grains. Both types of fluid and pore pressure distributions can occur in several important geological systems: The nature of oil/gas distribution in a pay zone affects the estimates of reserves, relative permeability, dry-frame elastic properties, and strength. The dry-

Cite this paper

@inproceedings{20011AS, title={1 Acoustic Signatures of Patchy Saturation}, author={}, year={2001} }