The Effects of Thermal Shock Due to Injection of Fluids on the Petrophysical Properties of Caprock and Reservoir Rocks: An Experimental Approach

Blake, Oshaine; Faulkner, Dan; Worden, Richard H.; Armitage, Peter

CO2 injection into oil fields and depleted hydrocarbon reservoirs is important for enhance oil recovery and carbon storage respectively. The injection not only alters the in-situ stress and geochemical conditions, but also the thermal properties of the storage domain. The temperature of the injected CO2 is usually considerably lower than the formation temperature. This will cause the rocks surrounding the injection well bore to be cooled rapidly, with the rate of cooling reducing with distance away from the well.

Previous work has identified heterogeneous horizontal permeabilities varying from the nanoDarcy to millidarcy range, and that change to the pore structure of lower permeability rocks has a greater effect on permeabilities than for the higher permeability rocks. Any change in the pore structure caused by thermal fracturing could have significant effects on the permeability of the reservoir and sealing units. Results from direct experiments of thermal fracturing of intact caprock and storage domain samples have not been published previously although it is clearly of vital importance in enhanced oil recovery and assessing the viability of CO2 geological storage systems.

We performed experiments involving oven heating of samples of caprocks and reservoir rocks from In Salah gas field, Algeria, to various temperatures (50-500°C) under reservoir stress conditions. The samples were then quenched in room temperature fluid, at ambient pressure conditions. A pore pressure of 20MPa and confining pressures 30MPa to 80MPa was used to simulate the change in effective reservoir stress conditions. The permeability and elastic wave properties (P- and S-waves) of the samples were measured pre and post-heat treatment. Thermal fracturing caused an increase in permeability up to 3 orders of magnitude and significant decrease in P- and S-waves velocity.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013