Temperature influence on permeability of Sioux quartzite containing mixtures of water and carbon dioxide

Abstract

CO2 sequestration in aquifers and depleted hydrocarbon reservoirs is a promising option for reducing atmospheric CO2. However, its implementation requires understanding how CO2 propagates and how it is stored in the reservoir. CO2 mixed with water exists in two forms, an immiscible phase (gas or liquid depending on the conditions of temperature and pressure) and a dissolved phase (a minor part of which reacts with H2O to form carbonic acid, H2CO3). The motion of CO2 in the reservoir is therefore a two-phase flow problem. Fluid/rock chemical reactions may also be important, but they are not considered here. When several immiscible fluids occupy the pore space, each phase may act as an obstacle to the motion of the others. Indeed, experimental evidence from oil production, vadose zone or CO2 sequestration studies [1] demonstrates that permeability is affected by the presence of a second phase in the pore space. The motion and spatial distribution of pore fluids (like water and carbon dioxide) are controlled not only by pore geometry and fluid pressure, but also by the viscosity, solubility, surface tension and wetting characteristics of each fluid phase [2], properties that usually vary with temperature. In the case of carbon dioxide and water, the solubility of CO2 is particularly sensitive to temperature. Thus, temperature variations may also affect the distribution and flow of the phases in the pore space. In this work, we measured the effect of temperature variations on the permeability of a rock saturated with a mixture of carbon dioxide and water. We used the oscillating pore pressure method (OPPM) developed by Kranz et al. [3] and Fischer et al. [4], because it minimizes fluid flux and, therefore, is not expected to disturb the phase distribution in the pore space as much as a steadily flowing fluid would. Although the method was devised to measure permeability of rocks with a single fluid phase, we can assess the effect of the second phase by comparing the permeability measurements made using a single fluid to those with a two-phase mixture.