Ronny Pini

Relative permeability and trapping of CO2 and water in sandstone rocks at reservoir conditions

[1] We report the results of an experimental investigation into the multiphase flow properties of CO2 and water in four distinct sandstone rocks: a Berea sandstone and three reservoir rocks from formations into which CO2 injection is either currently taking place or is planned. Drainage relative permeability and residual gas saturations were measured at 50 � C and 9 MPa pore pressure using the steady state method in a horizontal core flooding apparatus with fluid distributions observed using x-ray computed tomography. Absolute permeability, capillary pressure curves, and petrological studies were performed on each sample. Relative permeability in the four samples is consistent with general characteristics of drainage in strongly water-wet rocks. Measurements in the Berea sample are also consistent with past measurements in Berea sandstones using both CO2/brine and oil/water fluid systems. Maximum observed saturations and permeabilities are limited by the capillary pressure that can be achieved in the experiment and do not represent endpoint values. It is likely that maximum saturations observed in other studies are limited in the same way and there is no indication that low endpoint relative permeabilities are a characteristic of the CO2/water system. Residual trapping in three of the rocks is consistent with trapping in strongly water-wet systems, and the results from the Berea sample are again consistent with observations in past studies. This confirms that residual trapping can play a major role in the immobilization of CO2 injected into the subsurface. In the Mt. Simon sandstone, a nonmonotonic relationship between initial and residual CO2 saturations is indicative of a rock that is mixed or intermediate wet, and further investigations should be performed to establish the wetting properties of illite-rich rocks. The combined results suggest that the petrophysical properties of the multiphase flow of CO2/water through siliciclastic rocks is for the most part typical of a strongly water-wet system and that analog fluids and conditions may be used to characterize these properties. Further investigation is required to identify the wetting properties of illite-rich rocks during imbibition processes.

Measuring and Modeling the Competitive Adsorption of CO2, CH4, and N2 on a Dry Coal

Data on the adsorption behavior of CO 2, CH 4, and N 2 on coal are needed to develop enhanced coalbed methane (ECBM) recovery processes, a technology where the recovery of CH 4 is enhanced by injection of a gas stream consisting of either pure CO 2, pure N 2, or a mixture of both. The pure, binary, and ternary adsorption of these gases on a dry coal from the Sulcis Coal Province in Italy has been measured at pressures up to 180 bar and temperatures of 45 and 70 degrees C for the pure gases and of 45 degrees C for the mixtures. The experiments were performed in a system consisting of a magnetic suspension balance using a gravimetric-chromatographic technique. The excess adsorption isotherms are successfully described using a lattice density functional theory model based on the Ono-Kondo equations exploiting information about the structure of the coal, the adsorbed gases, and the interaction between them. The results clearly show preferential adsorption of CO 2 over CH 4 and N 2, which therefore indicate that ECBM may be a viable option for the permanent storage of CO 2.

Experimental analysis of spatial correlation effects on capillary trapping of supercritical CO2 at the intermediate laboratory scale in heterogeneous porous media

Author(s): Trevisan, L; Pini, R; Cihan, A; Birkholzer, JT; Zhou, Q; Illangasekare, TH | Abstract:

Imaging and quantification of spreading and trapping of carbon dioxide in saline aquifers using meter‐scale laboratory experiments

The role of capillary forces during buoyant migration of CO2 is critical toward plume immobilization within the postinjection phase of a geological carbon sequestration operation. However, the inherent heterogeneity of the subsurface makes it very challenging to evaluate the effects of capillary forces on the storage capacity of these formations and to assess in situ plume evolution. To overcome the lack of accurate and continuous observations at the field scale and to mimic vertical migration and entrapment of realistic CO2 plumes in the presence of a background hydraulic gradient, we conducted two unique long-term experiments in a 2.44 m × 0.5 m tank. X-ray attenuation allowed measuring the evolution of a CO2-surrogate fluid saturation, thus providing direct insight into capillarity-dominated and buoyancy-dominated flow processes occurring under successive drainage and imbibition conditions. The comparison of saturation distributions between two experimental campaigns suggests that layered-type heterogeneity plays an important role on nonwetting phase (NWP) migration and trapping, because it leads to (i) longer displacement times (3.6 months versus 24 days) to reach stable trapping conditions, (ii) limited vertical migration of the plume (with center of mass at 39% versus 55% of aquifer thickness), and (iii) immobilization of a larger fraction of injected NWP mass (67.2% versus 51.5% of injected volume) as compared to the homogenous scenario. While these observations confirm once more the role of geological heterogeneity in controlling buoyant flows in the subsurface, they also highlight the importance of characterizing it at scales that are below seismic resolution (1–10 m).

A calibration-free approach for measuring fracture aperture distributions using X-ray computed tomography

Various methods have been proposed to measure fracture aperture distributions, including X-ray computed tomography (CT) imaging, which has the advantage that it can be combined with dynamic flow experiments. In this paper, we present a calibration-free missing CT attenuation (CFMA) imaging method for measuring fracture apertures that avoids time-consuming calibration. In addition, this model does not assume a homogeneous matrix and thus provides a good estimate of fracture apertures even when rock properties are heterogeneous. The validity of the CFMA model is established by four approaches: comparing apertures calculated with the conventional calibration-based method; evaluating model predictability at different scanner voxel sizes; comparing with calibration coefficients in the literature from a number of experiments with different rocks and X-ray scanners; and comparing aperture measurements for dry and wet scans. We analyze the systematic error and the random error introduced by rock heterogeneities and CT scanning and show that by averaging 5 replicate scans, we reduce the aperture measurement error to ∼22 µm.

Multidimensional Quantitative Imaging of Gas Adsorption in Nanoporous Solids

X-ray computed tomography is applied to image gas adsorption in nanoporous solids. The equations are developed to calculate rigorous measures of adsorption, such as the excess adsorbed amount, by applying a dual-scanning technique. This approach is validated by considering the CO2/13X zeolite system in a fixed-bed adsorber, and multidimensional patterns are obtained of key characteristic properties, such as bed porosity, excess adsorption, and density of the adsorbed phase. The quantification of the spatial variability of the adsorbed amount within the system represents a major novelty with regards to conventional techniques. The ability to quantify adsorption with such a level of observational detail discloses unparalleled opportunities to interrogate and revisit adsorption processes in porous media.

Laboratory Studies to Understand the Controls on Flow and Transport for CO2 Storage

Abstract We review outcomes from laboratory studies that target CO2 flow and transport in the subsurface across the scales from microns to meters. A key distinctive feature of the CO2/brine system is that it tends to be more capillary dominated than the oil/water system, because of the low viscosity of CO2 as compared to brine. This increases the importance of rock heterogeneity in governing fluid displacement and introduces challenges for researchers to make reliable measurements of characteristic transport (e.g., dispersivity) and multiphase flow properties (e.g., relative permeability and trapping curves). Accurate parameterization of rock heterogeneity can nowadays be achieved thanks to a more widespread use of imaging technology, such as X-ray Computed Tomography, coupled with numerical simulations. This enables identifying general rules for experiment design and to extend experiments to conditions (e.g., flow rates) prevalent in the subsurface, which would be otherwise not attainable in the laboratory. Data gaps still exist, particularly with respect to the characterization of mixed-wet systems, of the hysteretic behavior of capillary pressure and relative permeability curves and of the mixing process at subsurface conditions.

Multidimensional Observations of Dissolution-Driven Convection in Simple Porous Media Using X-ray CT Scanning

We present an experimental study of dissolution-driven convection in a three-dimensional porous medium formed from a dense random packing of glass beads. Measurements are conducted using the model fluid system MEG/water in the regime of Rayleigh numbers,

Capillary pressure and heterogeneity for the CO2/water system in sandstone rocks at reservoir conditions

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