Acoustic Behavior of Sedimentary Rocks: Geological Properties Versus Poisson's Ratios

Verwer, Klaas¹, Hendrik Braaksma², Jeroen Kenter³ (1) Vrije Universiteit, Amsterdam, Netherlands (2) Universite Montpellier 2, Montpellier, France (3) Chevron Energy Technology Company, Voorburg, Netherlands

Velocity transforms are fundamental tools for the extraction of geological information from seismic reflection data sets and or predicting porosity from wireline logging data. Most commonly used transform are all based on empirical relationships extracted from relatively small, “clean”, mono- and bi-mineral and mostly siliciclastic data sets and generally fail to explain the acoustic relationships within multi-mineral data sets. To extract globally significant relationships between geological and acoustic parameters, over 2800 plug measurements were collected from own measurements (more than two-thirds of the data) and the literature. Fundamental parameters that control the mechanical properties of the different sediment groups are rock texture and mineralogy, typical “geological properties”. Using cross plots of Poisson's ratio versus compressional wave impedance (including shear wave properties) rock texture can be differentiated. Sedimentary rocks that have retained their granular texture largely overlap and include carbonates and siliciclastics, whereas rocks that are recrystallized, and as a consequence have lost that character, occupy a completely different area in the cross plots. Rocks that have a transitional character are found to connect both regions. The results demonstrate an intimate relationship between mechanical behavior and the primary as well as diagenetic overprint of the sedimentary rocks and allow the direct extraction of crystalline, granular and mixture behavior and, secondly, the relative mineral composition within those groups. This relative simple approach may have great significance for the general prediction of rock types and index properties from seismic data sets and in well bores.