Possible Seismic Effects of Geochemical Processes of Injection of Carbon Dioxide in Carbonate Reservoirs.

Abstract

The seismic effect of geochemical reactions caused by rock-fluid interactions have been investigated throughout this thesis. Seismic attributes can provide valuable information about rock properties. As a result, rock physics models are important to link geological and seismic parameters. Traditional fluid substitution models only consider the rock’s response to variations in pore fluid. However, fabric alterations are not evaluated. Carbonate rocks hold a rock fabric highly prone to geochemically induced alterations. Research on revealing possible geochemical effects from CO2 injections in carbonates, display a variety of textural alterations following rock-fluid interaction. As porosity and pore-shape affect the seismic properties, alterations in the rock fabric may induce large variations in the seismic response. By performing rock physics modelling, the effect of various geochemical processes has been evaluated. Fluid substitution models display the effect of pore fluids on the seismic properties of a porous reservoir. Based on experimental research, scenarios describing possible fabric alterations following rock-fluid interactions are defined. The results reveal that fabric alterations mainly occur in the pore space, either altering the pore volume or pore geometry. Trough implementation of forward rock physics modelling, the effects of pore geometry and pore volume on the seismic properties are investigated. The variations in seismic velocities and elastic properties are larger than those estimated when considering only the fluid effects. In addition, forward seismic modeling reveals the effect of fabric alterations on the amplitude versus incident-angle response. Evaluations of the results show that the seismic effects of poreshape are different than the effects of pore volume. By including the effect of pore-pressure and compaction, mechanical deformation is incorporated into the final stage of the modelling. This effect has however not displayed significant alterations in the seismic response of the carbonate rock model. The work has demonstrated the importance of evaluating alterations occurring in the rock frame following rock-fluid interactions, in addition to the effect of fluids.