Effects of overconsolidation on seismic rock physics — A comparative study between unconsolidated sands and weakly cemented sandstone

Abstract

In seismic rock physics, models typically assume rocks are normally consolidated, often neglecting the effects of overconsolidation. Recent studies reveal that overconsolidated sands, resulting from stress release, show different physical property variations than normally consolidated sands. However, similar research is lacking for weakly cemented sandstones, a common reservoir analog. This study aims to systematically compare the effects of overconsolidation and stress direction on unconsolidated sandstones and weakly cemented sandstones. It also assesses the impact of overconsolidation on seismic interpretation, monitoring, and rock physics modeling applied to the two types of rocks. Experimental measurements of porosity, P-wave, and S-wave velocities were collected under different stress paths between loading and unloading. For weakly cemented sandstone, well-log data from the Norwegian Sea and Barents Sea were compared with experimental data. Analyses focused on the velocity-porosity relationship, VP/VS ratio vs. AI, and VP/VS ratio vs. effective stress.