Rock acoustics of diagenesis and cementation

TL;DR

This study models how diagenesis, cementation, and compaction affect the elastic properties of shales and sandstones, providing a simple method to predict seismic velocities based on geological processes and temperature history.

Contribution

It introduces a basin-evolution model integrating four petro-elastical theories to simulate elastic property changes during diagenesis and cementation, accounting for mineral transformations and effective pressure effects.

Findings

Seismic velocities increase with depth and temperature.

Different petro-elastical models produce similar velocity predictions.

The methodology enables velocity estimation based on geological history.

Abstract

We simulate the effects of diagenesis, cementation and compaction on the elastic properties of shales and sandstones with four different petro-elastical theories and a basin-evolution model, based on constant heating and sedimentation rates. We consider shales composed of clay minerals, mainly smectite and illite, depending on the burial depth, and the pore space is assumed to be saturated with water at hydrostatic conditions. Diagenesis in shale (smectite/illite transformation here) as a function of depth is described by a 5th-order kinetic equation, based on an Arrhenius reaction rate. On the other hand, quartz cementation in sandstones is based on a model that estimates the volume of precipitated quartz cement and the resulting porosity loss from the temperature history, using an equation relating the precipitation rate to temperature. Effective pressure effects (additional compaction) are accounted for by using Athy equation and the Hertz-Mindlin model. The petro-elastic models yield similar seismic velocities, despite the different level of complexity and physics approaches, with increasing density and seismic velocities as a function of depth. The methodology provides a simple procedure to obtain the velocity of shales and sandstones versus temperature and pressure due to the diagenesis-cementation-compaction process.