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. 2024 Jul 9;14(1):15852.
doi: 10.1038/s41598-024-65920-6.

Enhanced carbon dioxide drainage observed in digital rock under intermediate wetting conditions

Affiliations

Enhanced carbon dioxide drainage observed in digital rock under intermediate wetting conditions

Jaione Tirapu Azpiroz et al. Sci Rep. .

Abstract

Carbon dioxide (CO 2 ) trapping in capillary networks of reservoir rocks is a pathway to long-term geological storage. At pore scale, CO 2 drainage displacement depends on injection pressure, temperature, and the rock's interaction with the surrounding fluids. Modeling this interaction requires adequate representations of both capillary volume and surface. For the lack of scalable representations, however, the prediction of a rock's CO 2 storage potential has been challenging. Here, we report how to represent a rock's pore space by statistically sampled capillary networks (ssCN) that preserve morphological rock characteristics. We have used the ssCN method to simulate CO 2 drainage within a representative sandstone sample at reservoir pressures and temperatures, exploring intermediate- and CO 2 -wet conditions. This wetting regime is often neglected, despite evidence of plausibility. By raising pressure and temperature we observe increasing CO 2 penetration within the capillary network. For contact angles approaching 90 , the CO 2 saturation exhibits a pronounced maximum reaching 80 % of the accessible pore volume. This is about twice as high as the saturation values reported previously. For enabling validation of our results and a broader application of our methodology, we have made available the rock tomography data, the digital rock computational workflows, and the ssCN models used in this study.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Simplified network methodology. (a) Schematic workflow from rock tomography to flow properties. Distribution of (b) capillary diameter and (c) capillary connectivity for the capillary network of the original Berea sandstone rock sample as a reference and a statistically simplified one for comparison.
Figure 2
Figure 2
CO2 saturation as function of pressure and contact angle. (a) Distributional map of the maximum CO2 saturation as a function of applied pressure gradient and contact angle, respectively, at a temperature of 473 K. (b) Maximum CO2 saturation as function of contact angle for representative pressure gradients at a temperature of 473 K. (c) CO2 saturation along C cutline at a pressure gradient of 1×106 Pa/m for representative temperatures.
Figure 3
Figure 3
Efficiency and security of CO2 drainage saturation and retention towards capillary trapping potential. Green color shades represent the CO2-wet regime, blue shades correspond to the water-wet regime, and red shades identify contact angles close to 90. The temperature is set to 473 K. Colors represent contact angle while symbols represent pressure gradient. Larger symbols represent higher pressure gradients. The legend is common to both plots. (a) CO2 saturation at 90% of the maximum value as a function of the injected volume required to reach that value. Injected volume larger than 1 PV represents scCO2 that is not stored within the sample. (b) Relation of maximum weighted CO2 saturation (wS) to injected volume across simulated conditions, aimed at increasing saturation close to the diagonal for maximum injection utilization.

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