Yves Gensterblum

High-pressure methane and carbon dioxide adsorption on dry and moisture-equilibrated Pennsylvanian coals

In the context of research on the reduction of CO2 emissions and the production of coalbed methane (CBM), high pressure adsorption measurements of CH4 and CO2 have been performed on dry and moisture-equilibrated Pennsylvanian coals of different rank (0.72, 1.19 and 1.56% VRr). Adsorption isotherms of the two gases were measured up to pressures of 20 MPa (200 bar), at 40, 60 and 80 °C using a volumetric method. Total excess sorption capacities for methane on dry coals ranged between 11 and 14 Std. cm3/g coal. The 40 °C sorption isotherms showed a saturation behavior while the 60 and 80 °C isotherms exhibited a monotonous increase over the entire experimental pressure range (up to 20 MPa). Methane sorption capacities of moisture-equilibrated coals were lower by ∼20–25% than those for dry coals and ranged between 7 and 11 Std. cm3/g coal. No distinct maturity effect was discernible for methane adsorption on the three samples studied, neither in the dry nor in the moist state. CO2 adsorption isotherms for dry and moist coals showed substantial differences. For dry coals the highest CO2 excess sorption capacities were observed at 40 °C with maximum values of 70 Std. cm3/g within limited pressure ranges. Carbon dioxide excess sorption for the moisture-equilibrated coals was usually lower than for the dry samples in the low pressure range. All high-pressure CO2 adsorption isotherms for moist samples were bimodal with distinct minima and even negative excess sorption values in the 8–10 MPa (80–100 bar) range. Beyond this range CO2 adsorption capacity increased with increasing pressure. High-temperature (80 °C) sorption capacities for CO2 were very low (<5 Std. cm3/g) in the low-pressure range but reached much higher levels (25–50 Std. cm3/g) above 12 MPa. The strong bimodal character of the CO2 excess isotherms on moist coals is interpreted as the result of a swelling effect caused by supercritical CO2 and enhanced by water. Some extent of swelling was also inferred for dry coals. Absolute sorption isotherms for CO2 were calculated assuming a sorbed-phase density of 1028 kg/m3 and compared with literature data. Like the excess isotherms, the absolute isotherms show a distinct decline in the 8–10 MPa pressure interval. At higher pressures, however, they increase monotonously.

Methane and CO2 sorption and desorption measurements on dry Argonne premium coals: pure components and mixtures

Abstract Sorption and desorption behaviour of methane, carbon dioxide, and mixtures of the two gases has been studied on a set of well-characterised coals from the Argonne Premium Coal Programme. The coal samples cover a maturity range from 0.25% to 1.68% vitrinite reflectance. The maceral compositions were dominated by vitrinite (85% to 91%). Inertinite contents ranged from 8% to 11% and liptinite contents around 1% with one exception (Illinois coal, 5%). All sorption experiments were performed on powdered (−100 mesh), dry coal samples. Single component sorption/desorption measurements were carried out at 22 °C up to final pressures around 51 bar (5.1 MPa) for CO 2 (subcritical state) and 110 bar (11 MPa) for methane. The ratios of the final sorption capacities for pure CO 2 and methane (in molar units) on the five coal samples vary between 1.15 and 3.16. The lowest ratio (1.15) was found for the North Dakota Beulah-Zap lignite (VR r =0.25%) and the highest ratios (2.7 and 3.16) were encountered for the low-rank coals (VR r 0.32% and 0.48%) while the ratio decreases to 1.6–1.7 for the highest rank coals in this series. Desorption isotherms for CH 4 and CO 2 were measured immediately after the corresponding sorption isotherms. They generally lie above the sorption isotherms. The degree of hysteresis, i.e. deviation of sorption and desorption isotherms, varies and shows no dependence on coal rank. Adsorption tests with CH 4 /CO 2 mixtures were conducted to study the degree of preferential sorption of these two gases on coals of different rank. These experiments were performed on dry coals at 45 °C and pressures up to 180 bar (18 MPa). For the highest rank samples of this sequence preferential sorption behaviour was “as expected”, i.e. preferential adsorption of CO 2 and preferential desorption of CH 4 were observed. For the low rank samples, however, preferential adsorption of CH 4 was found in the low pressure range and preferential desorption of CO 2 over the entire pressure range. Follow-up tests for single gas CO 2 sorption measurements consistently showed a significant increase in sorption capacity for re-runs on the same sample. This phenomenon could be due to extraction of volatile coal components by CO 2 in the first experiment. Reproducibility tests with methane and CO 2 using fresh sample material in each experiment did not show this effect.

High-pressure adsorption of methane, carbon dioxideand their mixtures on coals with a special focus on the preferential sorption behaviour

Abstract During recent years, extensive studies have been undertaken at RWTH Aachen to assess the gas adsorption capacities of coals of different rank with respect to CH 4 , CO 2 and their mixtures [e.g. Int. J. Coal Geol. 51 (2002) 69; Proceedings JCOAL Workshop: Present Status and Perspective of CO 2 Sequestration in Coal Seams, Tokyo, Japan, (5 September 2002) 23–38]. Excess sorption isotherms of carbon dioxide recorded at 40, 60 and 80 °C on dry and moisture-equilibrated Carboniferouscoals from the Netherlands exhibited distinct minima and even negative values in the 8–12 MPa interval. These anomalies are indicative of a strong volumetric effect. Evaluation of the experimental results in terms of absolute sorption assuming a range of different densities for the adsorbed phase could not eliminate the observed anomalies. In consequence, substantial swelling (up to 20%) of the (powdered) coal samples must be invoked to account for the observed phenomena. This interpretation is supported by the results of field tests in Alberta, Canada [Proceedings JCOAL Workshop: Present Status and Perspective of CO 2 Sequestration in Coal Seams, Tokyo, Japan, (5 September 2002) 59–66], which resulted in a significant reduction in coal-seam permeability upon CO 2 injection. The latest research focuses on the preferential sorption behaviour of CO 2 and CH 4 of coals from the Silesian coal basin. Experiments are conducted at pressures up to 250 bar (25 MPa) at a temperature of 45 °C using the volumetric method. These measurements provide fundamental information for enhanced coalbed methane recovery (ECBM) and storage of CO 2 in deep unminable coal seams proposed as a potential means of the reduction of anthropogenic CO 2 emissions (RECOPOL-project: //www.nitg.tno.nl/recopo/ ). Preferential adsorption experiments on dry and moisture-equilibrated coals of different rank under identical conditionsshowed that adsorption is a function of coal type, moisture content and pressure. While at pressures above 50 bar, CO 2 was always adsorbed preferentially to methane, preferential sorption of methane was observed in some instances at lower pressures. The unexpected phenomenon of preferential CH 4 adsorption on natural coals is presently an issue for further investigation. In the context of a round robin project initiated by the US Department of Energy, CO 2 excess sorption isotherms have beendetermined on five US premium coals at 22 °C in the dry state. Diversities of the excess sorption behaviour of these coals under different rank can be observed. Generally, excess sorption isotherms of lignite and subbituminous coals (0.25–0.46% VRr) exhibited a monotonous increase over the entire experimental pressure range (up to ∼ 50 bar), while higher mature coals tended to approach a saturation level corresponding to a Langmuir isotherm.

Gas saturation and CO2 enhancement potential of coalbed methane reservoirs as a function of depth

The influence of moisture, temperature, coal rank, and differential enthalpy on the methane (CH4) and carbon dioxide (CO2) sorption capacity of coals of different rank has been investigated by using high-pressure sorption isotherms at 303, 318, and 333 K (CH4) and 318, 333, and 348 K (CO2), respectively. The variation of sorption capacity was studied as a function of burial depth of coal seams using the corresponding Langmuir parameters in combination with a geothermal gradient of 0.03 K/m and a normal hydrostatic pressure gradient. Taking the gas content corresponding to 100% gas saturation at maximum burial depth as a reference value, the theoretical CH4 saturation after the uplift of the coal seam was computed as a function of depth. According to these calculations, the change in sorption capacity caused by changing pressure, temperature conditions during uplift will lead consistently to high saturation values. Therefore, the commonly observed undersaturation of coal seams is most likely related to dismigration (losses into adjacent formations and atmosphere). Finally, we attempt to identify sweet spots for CO2-enhanced coalbed methane (CO2-ECBM) production. The CO2-ECBM is expected to become less effective with increasing depth because the CO2-to-CH4 sorption capacity ratio decreases with increasing temperature and pressure. Furthermore, CO2-ECBM efficiency will decrease with increasing maturity because of the highest sorption capacity ratio and affinity difference between CO2 and CH4 for low mature coals.

High-Pressure/High-Temperature Methane-Sorption Measurements on Carbonaceous Shales by the Manometric Method: Experimental and Data-Evaluation Considerations for Improved Accuracy

In exploration for shale gas, experimental methane-sorption measurements represent a valuable source of information for resource estimates and for reservoir-modeling studies. Here, the main difficulty is the relatively low adsorption capacity of shales (typically 10% of the sorption capacity of coals), as well as the fact that the measurements need to be performed over a wide range of pressures and temperatures characteristic of past or present geological conditions. In this work, we demonstrate the capabilities of an adapted manometric apparatus to reliably measure excess sorption isotherms at pressures of up to 30 MPa and temperatures up to 423 K on carbonaceous shales. This is accomplished with an experimental design comprising separate heating zones for the sample cell and for the rest of the apparatus. An experimental and mass-balance approach is presented to quantify the temperature gradient existing between the two heating zones, as well as the thermal expansion of the sample cell, and to account for these in the calculation of the excess sorption. We demonstrate that the analysis of the helium-void-volume data over a large temperature range can be interpreted with respect to the thermal expansion of the sample and, in some cases, changes in pore-volume accessibility to helium. We propose to perform blank-expansion tests with non-adsorbing specimens (e.g., steel cylinders) as a quality check to eliminate device-specific artifacts resulting from unknown measurement uncertainties or from uncertainty in the equation of state. Two evaluation procedures are presented to quantitatively account for the blank tests in the final result of sorption measurements on shale samples. As an example, methane-sorption isotherms for carbonaceous shale at 311, 338, 373, and 423 K are presented. By use of a Monte Carlo algorithm to simulate the propagation of the experimental uncertainties, the final estimated uncertainty in excess sorption resulting from systematic errors was found to be6 0.007 mmol/g at 25 MPa. The consideration of the blank-expansion tests in the mass balance further reduces the systematic error, at least to a point at which an excellent intralaboratory consistency is obtained. The estimated uncertainty resulting from random errors was found to significantly overestimate the actual precision of the experimental setup, and an explanation is provided with respect to experimental design. A datareduction approach using an excess-sorption function based on a Langmuir-type absolute-sorption model was found to provide an excellent representation of the measured sorption data. By means of simplified model calculations we demonstrate that the excesssorption formalism is a sufficient, simple, and adequate approach to applications in shale-gas-resource estimation. The uncertainties pertaining to representativeness of experimental sorption data of in-situ reservoir conditions are briefly discussed.

CO2 and CH4 sorption kinetics on coal: An experimental and modeling approach

Publisher Summary Coalbed methane (CBM) production combined with carbon dioxide (CO2) injection is currently an issue of intense investigation worldwide. On the European level, the feasibility of CO2 storage in coal seams is currently being investigated in the RECOPOL project, which involves laboratory tests, numerical modeling, and a pilot injection into a Carboniferous coal seam in Silesia/Poland. Apart from the thermodynamic processes in a coal seam, one aspect of major importance for CO2 storage and CO2-enhanced CBM recovery is the rate of CO2 adsorption and CH4 desorption. To address this issue, adsorption kinetic experiments with both CO2 and CH4 were performed on six different grain size fractions (<0.063 mm to ∼3 mm) of a coal sample from the Upper Silesian Coal Basin in Poland. Experiments were run on dry and moist coals at two different temperatures (45 and 32°C). The purposes of this study were: (1) to define a simple empirical model describing the adsorption rates of the two gases, (2) to attempt an extrapolation of the data from the laboratory to the reservoir scale, (3) to relate sorption isotherms to different coal properties of different particle sizes, and (4) to contribute to a better understanding of the combined C02-storage and CBM-production technologies.

“CO2RINA”—CO2 Storage Risk Integrated Analysis

While risk assessment for CO2-storage often has been conducted by using a lot of simplifications and conservatisms, our approach developed in the CO2RINA-research project is based on the integration of all models, existing at a moment in time. These models will be coupled by the so called transfer function approach which has been proven to be very powerful in the risk assessment for low level radioactive waste. This concept ensures, that the risk assessment is always consistent with the state of the models existing for a specific site. It can be immediately improved if the existing models will be improved over time. The approach was verified by comparison of the direct coupling of different process models in an overall model with a coupling by transfer functions by conducting a wide range of test calculations showing very good accuracy of the approach. The new coupling approach allows the incorporation of a variety of additional effects which are difficult to handle in an overall model. Examples for such processes are complex chemical and microbiological interactions, geomechanical feedback loops and migration of CO2 in the atmosphere. In the project there have been developed specified models for a generic site with parameters similar to the Ketzin site. These models include a reservoir model, a model for the alteration of the cementation of a mature well, a fault model, a model describing advection and diffusion through the cap rock, a complex model for the migration in a Quaternary aquifer including complex chemical interactions and a geomechanical model. Additionally there was shown the way of integration of microbiological processes which have been modelled in detail in the CO2BIOPERM project. The new approach is ready to be adapted to a specific CO2-storage site.

Clay/CO2 Interactions in the Context of Geological Storage of Carbon Dioxide

A major concern when storing CO2 in geological formations is the sealing efficiency of lowpermeable sequences overlying potential storage reservoirs. The long-term integrity of these sealing layers (caprocks) is a prerequisite to maintain CO2 in place and avoid dissipative loss to the atmosphere. Such leakage will occur either by capillary leakage, via diffusion or through existing or induced faults and fractures The assessment of leakage risks and leakage rates, considering different potential mechanisms, is therefore an important issue for site approval and public acceptance.