Karl-heinz Wolf

Carbon capture and storage (CCS) has the potential for eliminating CO2 emissions to atmosphere. This option includes storage strategies such as CO2 injection into deep saline aquifers, depleted oil and gas reservoirs, and unmineable coal seams. This process is largely controlled by the interactions between CO2 , the reservoir fluid and reservoir rock. In particular, the wettability of the rock matrix has a strong effect on the distribution of the injected CO2 into geological formations. In this study, the wetting behavior of Bentheimer sandstone slabs and CO2 and/or flue gas is investigated by means of contact-angle measurements. In addition, the interfacial tension between CO2 and/or flue gas and connate water was measured. The experiments were conducted in a pendant-drop cell, adapted to allow captive-bubble contact-angle measurements and performed at a constant temperature of 318 K and pressures varying between 0.2-15 MPa, typical in-situ conditions.

ABSTRACT The success of CO2 storage in deep saline aquifers and depleted oil and gas reservoirs is largely controlled by interfacial phenomena among fluid phases and rock pore spaces. Particularly, the wettability of the rock matrix has a strong effect on capillary pressure, relative permeability, and the distribution of phases within the pore space and thus on the entire displacement mechanism and storage capacity. Precise understanding of wettability behavior is therefore fundamental when injecting CO2 into geological formations to sequestrate CO2 and/or to enhance gas/oil production. In this study, the contact angles of Bentheimer sandstone/water/CO2 or flue gas have been evaluated experimentally using the captive-bubble technique in the pressure range from 0.2 to 15 MPa. The experiments were conducted using different compositions of aqueous phase with respect to CO2, i.e., unsaturated and fully saturated. It has been shown that a reliable contact-angle determination needs to be conducted using a pre-equilibrated aqueous phase to eliminate dissolution effects. In the fully saturated aqueous phase, the Bentheimer sandstone/water system is (and remains) water-wet even at high pressures against CO2 and/or flue gas. In these systems, the data of the stable contact angle demonstrate a strong dependence on the bubble size, which can be mainly explained by the gravity (buoyancy) effect on bubble shape. However, the surface nonideality and roughness have significant influence on the reliability of the contact-angle determination. The results of this study prove that in order to avoid the dependency of the contact angle on the bubble size in these systems, the effect of gravity (buoyancy) on bubble shape has to be considered by calculation of the Bond number; for systems characterized by Bond numbers less than 0.9, the influence of the bubble radius on the contact angle becomes insignificant. The experimental results show that, in contrast to quartz, the phase transition of CO2 from subcritical to supercritical has no effect on the wettability of the Bentheimer sandstone/water system, which originates from differences in the surface charges of quartz and Bentheimer sandstone. In an unsaturated system, two dissolution regimes are observed, which may be explained by density-driven natural convection and molecular diffusion.

ABSTRACT Carbonated Water Flooding (CWF) is an EOR method that utilises CO2 to enrich water. CWF is a technique that has the potential to minimize problems arising during CO2 flooding and at the same time is a safe and continuous method for capture and storage of CO2. It demonstrates satisfactory sweep efficiency due to the comparable viscosities of CW and oil and slower CO2 breakthrough (Jackson, 2000). One of the important aspects of the CWF process is molecular diffusion of CO2 from carbonated water into oil (DCWO). We examine DCWO in the laboratory by visualization of oil swelling and recovery over time. We conducted displacement experiments at reservoir conditions. Oil, that is entrapped in a dead end pore (DEP) by interfacial tension, viscous force, gravity and pressure, is flooded with carbonated water at supercritical CO2 conditions. Results show that a water barrier can occur, postponing the CO2-oil contact from the CO2 source and increasing pressure may lead to reducing process time. The results of the conducted CW flooding experiments may provide a link to towards implementation of the CWF process on the larger scale with an option for CO2 sequestration.

ABSTRACT The use of coal seams as reservoirs implies that new ways of coal characterization are required. The storage capacity of coal has to be related to the ability of gases and fl uid to migrate through a coal seam. Sorption and diffusion behaviour of the matrix and the cleat related Darcy permeability are the most important parameters for the determination of its reservoir properties. A new method for assessment of interfacial phenomena associated with carbon dioxide and methane transport/sorption processes in coals is presented. The article describes two innovative kinds of laboratory experiments. The fl ushing experiments characterize the fl ow properties of a solid coal core under simulated in-situ conditions. The pendant drop cell experiment characterizes the interactions of coal, water, carbon dioxide and methane. For that reason the equipment and experimental procedures of two fl ushing devices and the set-up of a trans-formed pendant-drop cell are explained. Besides procedures, technical diffi culties, pitfalls and general interpretations are discussed in experimental examples. One of the major issues is, "how the experimental results are combined with known geo-parameters, in order to be used as input parameters at cleat and fi eld scale".