Seismic and Rock Physics Diagnostics of Multiscale Reservoir Textures

Abstract

As part of our study on "Relationships between seismic properties and rock microstructure", we have 1. Studied relationships between velocity and permeability. 2. Used independent experimental methods to measure the elastic moduli of clay minerals as functions of pressure and saturation. 3. Applied different statistical methods for characterizing heterogeneity and textures from scanning acoustic microscope (SAM) images of shale microstructures. 4. Analyzed the directional dependence of velocity and attenuation in different reservoir rocks 5. Compared Vp measured under hydrostatic and non-hydrostatic stress conditions in sands. 6. Studied stratification as a source of intrinsic anisotropy in sediments using Vp and statistical methods for characterizing textures in sands.4 INTRODUCTIONIn this quarter, we submit results of our research on: impedance mapping on a micrometer scale and its relation to centimeter-scale core measurements of impedance, measurements of clay mineral modulus and the seismic properties of unconsolidated sediments at very low effective pressures. We have also begun work on analyzing the effects of scales on textural, impedance and velocity anisotropy and heterogeneity in consolidated and in unconsolidated materials. Six papers have been published on the work done in this year of the project. This report presents reprints of our publications relevant to this project on impedance mapping, acoustic measurements, and scales analyses. 9 PAPER 1Prasad, M., Velocity-permeability relations within hydraulic units. Velocity-permeability relations within hydraulic unitsManika Prasad * ABSTRACTRelationships between seismic velocity and permeability have been difficult to establish. I show that by grouping and sorting rocks into hydraulic units, we can establish relationships between velocity and permeability. The hydraulic units are calculated from measured porosity and permeability values. Correlation between velocity and permeability is significant within each hydraulic unit (the correlation coefficient, R 2 , lies in the range 0.65-0.87). This correlation is an extension of the match between porosity and permeability within a hydraulic unit. I show how the compaction and cementation history of a sediment can have effects on its physical properties such as porosity and permeability and on its seismic properties. The measured velocity data are further approximated with the Biot model. The velocitypermeability relation and modeling results are demonstrated for a large data set of laboratory measurements. The good match between calculated and measured data demonstrates that this relation can be used to predict permeability from velocity in well logs by zoning the data from training wells into hydraulic units. One possible application is shown where, by using site-specific data, the velocity-permeability relation is vastly improved with a correlation coefficient R 2 of 0.9.