Stefan Iglauer

Measurements of the capillary trapping of super‐critical carbon dioxide in Berea sandstone

[1]xa0We measure primary drainage capillary pressure and the relationship between initial and residual non-wetting phase saturation for a supercritical carbon dioxide (CO2)-brine system in Berea sandstone. We use the semi-permeable disk (porous-plate) coreflood method. Brine and CO2 were equilibrated prior to injection to ensure immiscible displacement. A maximum CO2 saturation of 85% was measured for an applied capillary pressure of 296 kPa. After injection of brine the CO2 saturation dropped to 35%; this is less than the maximum trapped saturation of 48% measured in an equivalent n-decane (oil)-brine experiment. The dimensionless capillary pressure is the same to within experimental error for supercritical CO2-brine, n-decane-brine and a mercury-air system. CO2 is the non-wetting phase and significant quantities can be trapped by capillary forces. We discuss the implications for CO2 storage.

Measurement of Nonwetting-Phase Trapping in Sandpacks

Summary We measure the trapped nonwetting-phase saturation as a function of initial saturation in sandpacks. The application of the work is for carbon dioxide (CO2) storage in aquifers, where capillary trapping is a rapid and effective mechanism to render the injected fluid immobile: The CO2 is injected into the formation followed by chase-brine injection or natural groundwater flow that displaces and traps it. Current models to predict the amount of trapping are based on experiments in consolidated media; while CO2 is likely to be injected at depths greater than approximately 800 m to render it supercritical, it may be injected into formations that tend to have a higher porosity and permeability than deep oilfield rocks. We use analog fluids—water and refined oil—at ambient conditions. The initial conditions are established by injecting oil into vertical or horizontal sandpacks 0.6 m long at different flow rates and then allowing the oil to migrate under gravity. The packs are then flooded with water. The columns are sliced, and the residual saturation is measured with great accuracy and sensitivity by gas chromatography (GC). This method allows low saturations to be measured reliably. The trapped saturation initially rises linearly with initial saturation to a value of approximately 0.13, followed by a constant residual as the initial saturation increases further. This behavior is not predicted by the traditional Land (1968) model but is physically consistent with poorly consolidated media where most of the larger pores can be invaded easily at relatively low saturation and there is, overall, relatively little trapping. The best match to our experimental data is achieved with the Aissaoui (1983) and the Spiteri et al. (2008) trapping models.

Analysis of the Influence of Alkyl Polyglycoside Surfactant and Cosolvent Structure on Interfacial Tension in Aqueous Formulations versus n-Octane

Abstract We studied the influence of molecular structural elements of alkyl polyglycoside (APG) surfactants on the interfacial tension (IFT) in aqueous formulations against n-octane. This included the analysis of alkyl and aryl chain length, type and number of sugar-ring head, anomers, addition of cosolvents and effect of salt addition. We found that longer alkyl or aryl chains lead to lower IFT, consistent with data recorded for commercial (mixed) APGs. APGs with only one sugar-ring head had lower IFT than their analog maltose derivates (two-ring head). Intriguingly the stereochemistry of the sugar head (i.e. galactose versus glucose) and the type of anomer showed a significant influence on IFT. The n-octyl-α-D-glucopyranoside anomer had a lower IFT than the corresponding β-anomer. 1-octanol and 1-hexanol were efficient cosolvents consistent with the datasets observed for commercial APGs. Salt addition reduced IFT. Functional groups (aldehyde, amide-methoxy) integrated into the molecular architecture of the APG skeleton were efficient in terms of significantly reducing IFT, suggesting a strategy for the molecular design of advanced APG surfactants. We discuss the results in the context of the hydrophilic-lipophilic deviation (HLD) concept, which we modified so that IFT values are discussed instead of phase behavior.

Measurements of Non-Wetting Phase Trapping Applied to Carbon Dioxide Storage

Abstract We measure the trapped non-wetting phase saturation as a function of the initial saturation in sand packs. The application of the work is for carbon dioxide (CO 2 ) storage in aquifers where capillary trapping is a rapid and effective mechanism to render injected CO 2 immobile. We used analogue fluids at ambient conditions. The trapped saturation initially rises linearly with initial saturation to a value of 0.11 for oil/water systems and 0.14 for gas/water systems. There then follows a region where the residual saturation is constant with further increases in initial saturation.

Capillary Trapping in Carbonate Rocks

Carbonate reservoirs represent a possible geological storage option for carbon dioxide from anthropogenic sources. We conducted capillary trapping experiments on different carbonate rocks to assess their suitability for storage. We measured the trapped non-wetting phase saturation as a function of the initial non-wetting phase saturation and porosity. We used refined oil – with a density similar to that of supercritical CO2 – as the non-wetting phase and brine as the wetting phase. The experiments were performed at ambient temperature and slightly elevated pressures. Saturations were determined by mass and volume balance. We found that the trapped non-wetting phase saturation rises approximately linearly with initial saturation. The porosity was shown to have a significant effect on both initial saturation and residual saturation.The influence of effective stress was also investigated. It was shown that carbonates have significantly different stress behavior compared to sandstones. As the pressure of the non-wetting phase increases during primary drainage, the initial oil saturation increases to a maximum value and then decreases, as the fluid pressure affects the pore structure of the rock.

Residual Saturation of Water-Wet Sandstones: Experiments, Correlations and Pore-Scale Modeling

Displacement experiments using the porous plate method were conducted on water-wet sandstones to measure the capillary trapping of oil by waterflooding as a function of its saturation after primary drainage. Three sandstone samples ranging in porosity from 12.2% to 22.1% were considered. Experiments on two samples were conducted at an elevated temperature and back-pressure of 343K and 9MPa respectively; experiments on the third sample were conducted at ambient conditions (292 to 297K and 0.06 to 0.17MPa). Residual oil saturation increases monotonically, but with a decreasing gradient, as initial saturation increases.