The influence of pore space geometry on the entrapment of carbon dioxide by capillary forces
- Christopher Holst Pentland (Shell Netherlands Natural Gas) | Stefan Iglauer (Curtin University) | Oussama Gharbi (Imperial College) | Katsuhiro Okada (University of Tokushima) | Tetsuya Suekane (Tokyo Institute Of Technology)
- Document ID
- Society of Petroleum Engineers
- SPE Asia Pacific Oil and Gas Conference and Exhibition, 22-24 October, Perth, Australia
- Publication Date
- Document Type
- Conference Paper
- 2012. Society of Petroleum Engineers
- 4.3.4 Scale, 4.1.2 Separation and Treating, 1.2.3 Rock properties, 4.3.1 Hydrates, 5.6.1 Open hole/cased hole log analysis, 1.8.5 Phase Trapping, 5.5.2 Core Analysis, 5.1.1 Exploration, Development, Structural Geology, 5.2 Reservoir Fluid Dynamics, 1.6.9 Coring, Fishing, 5.3.2 Multiphase Flow, 6.4.1 Facility Vulnerability Assessment, 4.1.5 Processing Equipment, 2.4.3 Sand/Solids Control
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We investigate the characteristic properties of porous media that influence the entrapment of carbon dioxide (CO2) by capillary forces. It is known that different geological formations can trap different quantities of CO2 but the relationship between formation properties and trapping is poorly understood at present. Advances in micro computed tomography (µCT) techniques now allow the porous media and trapped CO2 clusters therein to be visualised and characterised on the micro meter scale. The context of this work is the geological storage of CO2 where the entrapment of injected CO2 by capillary forces on the pore scale is proposed as a fast and safe method to store injected CO2.
We analyse a series of saturated and unsaturated porous media using µCT; four glass bead packs, a sand pack and a sandstone. In the saturated images the pore space contains brine and residual CO2 (Sr) at subsurface storage conditions. We quantify Sr and cluster size distributions and determine characteristic properties of the porous media through image analysis and the extraction of representative networks. We show that media with narrower pore throats, such as sandstones, trap more CO2 than media with wider pore throats. Numerical simulations performed on the extracted networks do not accurately predict the measured residual CO2 saturations. We discuss the important implications of these results for CO2 storage site selection, containment security assessments, and storage capacity appraisal.
Capillary trapping - the immobilisation of non-wetting phase clusters on the pore scale by capillary forces - has been identified as an important subsurface mechanism in the geological storage of CO2 in saline aquifers. The magnitude of CO2 trapped by capillary forces (the residual saturation; Sr) will impact the migration of CO2 through the aquifer and the ultimate CO2 storage capacity, while the surface area of trapped clusters will be a controlling parameter in their ultimate dissolution in the formation brine.
Capillary trapping has been studied for decades due to its importance in the petroleum industry and in soil remediation, and more recently also in the context of CO2 storage (e.g. Jerauld, 1997, Conrad et al., 1992, Iglauer et al., 2011a respectively). Historically experiments were performed on centimetre scale samples (e.g. Oak et al., 1990) but recently such experiments have been performed on millimetre scale samples enabling the pore space and the fluids contained therein to be imaged on the micro-meter scale with micro-computed tomography (µCT) [Prodanovic et al., 2007; Iglauer et al., 2010, 2011b, 2012a, 2012b; Kumar et al., 2010; Georgiadis et al., 2011; Suekane et al., 2011; Porter et al. 2010].
Here we perform additional analysis on the storage condition (i.e. high pressure and elevated temperature) CO2-brine results of Iglauer et al., 2011b and Suekane et al., 2011. Table 1 summarises the conditions of these experiments. Our objective is to understand which characteristic properties of the porous media have the greatest influence upon capillary trapping, and to investigate the characteristic properties of the trapped clusters. We employ a multi stage approach: rock properties are determined from the unsaturated scans through image analysis and the generation of representative pore network models; cluster properties are determined by analysing the saturated scan images; and trapped CO2 saturations from the experiments are compared with those predicted by dynamic simulations on the pore network models.
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