Unmineable Coalbeds Research Articles

Importance of specific substrate utilization by microbes in microbially enhanced coal-bed methane production: A modelling study

This study addresses a major gap in the understanding and control of microbially enhanced coal-bed methane (MECBM) production. A mathematical and conceptual model comprises a food-web that includes two types of bacteria and three types of archaea representing substrate-specific members of the community; the microbial community members are potentially interacting by competing for or being inhibited by substrates or products of other microbial community members. The model was calibrated using data sets from two different experimental setups. The calibrated model effectively predicted the methane concentrations within a 7% range of deviation from the experimental results. The results of additional batch experiments using varied conditions are also reproduced in an attempt to validate the model and to test the hypothesis of amendment-induced stimulation of microbial community members capable of converting coal into substrates available to methane producing microbes. This study significantly enhances the understanding of the complex interactions between microbial activity, substrate-specificity and bio-availability of coal for methane production, and provides the basis for including hydraulic flow and transport processes into future mathematical models important for the design and implementation of more sustainable methods of harvesting methane from un-mineable coalbeds.

Compressibility of Supercritical Methane in Nanopores: A Molecular Simulation Study

Unmineable coalbeds are a promising source of natural gas and can act as a receptacle for CO2 sequestration. This is because they are composed of extensive nanoporous systems, which allow for signi...

Sequestration of carbon dioxide in coal: Energetics and bonding from first-principles calculations

Sequestration of CO2 in unmineable coalbeds is one of the attractive ways being investigated to reduce the CO2 concentration in the atmosphere. Extensive experimental studies have demonstrated that storage of CO2 molecules in coal seam involves both chemisorption and physisorption, but the underlying mechanism at the atomic scale has remained elusive. We report results of first-principles density-functional-theory calculations for the interaction between molecular CO2 and coal. The calculations show that chemisorption of CO2 in defective coal is possible, and CO2 can form chemical bonding with defective coal, particularly at the defects involving carbon and hydrogen vacancies and epoxy functional groups. On the other hand, formation of chemical bonding of CO2 with defect-free coal network is unlikely.

Molecular simulation studies of hydrocarbon and carbon dioxide adsorption on coal

Sorption isotherms of hydrocarbon and carbon dioxide (CO2) provide crucial information for designing processes to sequester CO2 and recover natural gas from unmineable coal beds. Methane (CH4), ethane (C2H6), and CO2 adsorption isotherms on dry coal and the temperature effect on their maximum sorption capacity have been studied by performing combined Monte Carlo (MC) and molecular dynamics (MD) simulations at temperatures of 308 and 370 K (35 and 97 °C) and at pressures up to 10 MPa. Simulation results demonstrate that absolute sorption (expressed as a mass basis) divided by bulk gas density has negligible temperature effect on CH4, C2H6, and CO2 sorption on dry coal when pressure is over 6 MPa. CO2 is more closely packed due to stronger interaction with coal and the stronger interaction between CO2 molecules compared, respectively, with the interactions between hydrocarbons and coal and between hydrocarbons. The results of this work suggest that the “a” constant (proportional to T 2 /P c ) in the Peng–Robinson equation of state is an important factor affecting the sorption behavior of hydrocarbons. CO2 injection pressures of lower than 8 MPa may be desirable for CH4 recovery and CO2 sequestration. This study provides a quantitative understanding of the effects of temperature on coal sorption capacity for CH4, C2H6, and CO2 from a microscopic perspective.

GEOLOGICAL CONSIDERATION FOR CO2 STORAGE IN INDONESIA: A BASINAL SCALE OUTLOOK

Carbon dioxide capture and storage (CSS) is alternative of reducing atmospheric emissions of CO2. The concepts of CO2 storage refer to the injection of carbon dioxide in dense form into aquifers, which basically must meet several conditions. Three types of geological formations that can be used for the geological storage of CO2 are oil and gas reservoirs, deep saline formations and unmineable coal beds. Indonesia has 60 Tertiary basins, however that great precautions must be taken for selecting particular sedimentary basin in Indonesia for carbon dioxide storage because of high possibility of leakage and the need to find deep formations as CO2 host since the geothermal gradient is high. One possibility to find proper basins is by selected “mature” basin as the detailed geological conditions are well known. Candidates are are North East Java or South Sumatra Basins. 
 
 Keywords: Carbon dioxide capture, storage, emission, basin.

Evaluation of coal swelling‐controlled CO2 diffusion processes

AbstractCO2 sequestration in deep and unmineable coalbeds is regarded as a viable option for carbon storage. CO2 diffusion is a key parameter determining the effectiveness of sealing CO2 in coal seams. By conducting laboratory tests of coal CO2 desorption and unsteady gas diffusion theory model calculations, the desorption dynamics of Yaojie coal were studied under the condition of constant temperature and varied balance pressures, and the CO2 diffusion coefficient was obtained using the non‐steady diffusion model at different times. The results show that the higher the balance pressure is, the greater the diffusion coefficient is under the same conditions. As the pressure drops, the CO2 diffusion coefficient gradually decreases as time increases, and the mass fraction of desorbed CO2 has a linear relationship with the diffusion coefficient. It was observed that under high pressures, the diffusion coefficient initially increases and then gradually decreases. The non‐steady CO2 diffusion in Yaojie coal is related to CO2‐induced swelling and to the effect of dissolved CO2 on the coal's structures and properties, especially under high‐pressure conditions. The glass transition of coal containing CO2 may be the governing factor leading to the nonlinear diffusion of CO2 in coal.

A preliminary evaluation of carbon dioxide storage capacity in unmineable coalbeds in China

In this study, CO2 storage capacity in unmineable coalbeds in China at depths of 1,000–2,000 m has been evaluated using the methodology recommended by CSLF. This evaluation is one part of the countrywide CO2 storage capacity evaluations in China, initiated by the Chinese Ministry of Land and Resources. This level of CO2 storage capacity evaluation gives a rough scale of assessment with the least site-specific detail. The results show that there is a storage capacity of 98.81 × 108 t CO2 in coalbeds buried at a depth range of 1,000–2,000 m and 4.26 × 1012 m3 additional coalbed methane can be recovered by CO2 injection. These results appear to show great potential and an attractive economic perspective of CO2 storage in unmineable coalbeds in China. Another part of this study is to classify the potential coalbed basins based on CO2 storage capacity and storage capacity per unit area. The study results reveal the distribution of the most potential basins for large-scale CO2 storage and the best economic basins for early CO2 storage in the future.

A chemo-poro-mechanical model for sequestration of carbon dioxide in coalbeds

To reduce the emissions of carbon dioxide into the atmosphere, it is proposed to inject anthropogenic carbon dioxide into deep geological formations. Deep, unmineable coalbeds are considered to be a possible carbon dioxide repository because coal is able to adsorb a large amount of carbon dioxide inside its microporous structure. However, the response of coalbeds is complex because of coupling between the flow and mechanical responses. Injection of carbon dioxide causes coal to swell, which leads to reductions in permeability and hence makes injection more difficult, and at the same time leads to changes in the mechanical properties that can affect the stress state in the coal and overlying strata. Apart from the influence of swelling on permeability, the chemo-mechanical aspects of carbon dioxide sequestration in coalbeds have been little studied. In this paper, the results of a series of triaxial tests on a bituminous coal are presented that show a reduction in elastic modulus as a result of carbon dioxide adsorption. Using these experimental results, a linear relationship between the reduction in elastic modulus and the amount of adsorbed gas was found. This relationship, in conjunction with a dual-porosity model, has been employed to simulate the hydromechanical response of a coal bed to carbon dioxide injection. The results of the numerical simulation show that the softening of the coal can change the permeability and stresses in the coal, and suggest that considering the softening effect is crucial for accurate assessment of the performance and safety of carbon dioxide storage in coalbeds.

Method for Simultaneous Measure of Sorption and Swelling of the Block Coal under High Gas Pressure

Carbon dioxide sequestration in unmineable coalbeds combined with enhanced coalbed methane recovery is attracting attention as one of the possible methods for carbon capture and storage. Sorption a...

Molecular simulation of CO2 adsorption in micro- and mesoporous carbons with surface heterogeneity

Abstract To mitigate and stabilize atmospheric CO 2 concentrations, alternate energy sources with zero carbon emissions offer ultimate solutions. However, technologies based on efficient and economic generation of electricity from non-carbonized energy sources are still in development. Therefore, carbon capture combined with sequestration as a component of a greater portfolio of solutions to reduce CO 2 emissions may be carried out during our transition from fossil-based resources to renewables or non-carbonized resources. As one of the attractive options, CO 2 captured by carbon-based sorbents as well as CO 2 sequestration in unmineable coalbeds require a thorough understanding of the adsorption properties in micro- and mesoporous carbon materials. An obstacle is insufficient understanding of the molecular-level mechanisms associated with CO 2 adsorption on realistic carbon pore surfaces with chemical heterogeneities and at pressures and temperatures characteristic of the depths of coal in the subsurface. Current fundamental investigations of gas adsorption onto functionalized carbon surfaces involve the characterization of carbon-based samples by experimental methods, understanding of electronic properties of functionalized carbon surfaces by density functional theory, and the thermodynamic property predictions using a Monte Carlo method within the grand canonical ensemble. With the consideration of surface chemistry, CO 2 storage capacity estimations in organic matrix of coal and gas shale increase greater than 40% when CO 2 is adsorbed in the ultramicropores, and greater than 15% in 2-nm micropores.

Variations in the mechanical behavior of Illinois bituminous coals

Unmineable coal beds are being considered as one of the geological sequestration options for storing carbon dioxide (CO2). The storage mechanisms and potential risks associated with the effects of CO2 on the coal structure are not yet understood and must be evaluated. The mechanical properties of the coal are expected to play an important role in the coal seams’ stability, especially under external perturbations. Typically, the mechanical characteristics of coal are investigated as a bulk material, which averages the effects of various structural inhomogeneities as well as of face and butt cleat fractures present in the coal. In this paper, we attempt to establish baseline mechanical characteristics of Illinois bituminous coals while minimizing the fracture effects. Rectangular coal strips (length <20mm), which showed no visible macro-defects, from two different Illinois bituminous coal seams, were subjected to three-point bending tests. Our results suggest there are significant variations in the flexural modulus (ranging from 0.7GPa to 3.4GPa) of the coal samples even though the coal rectangular strips originated from the same coal chunk. Vibrational spectroscopic analysis on the samples, which underwent mechanical testing, indicates a correlation between the flexural strength and modulus with the intensity of aliphatic groups. However, the mineral content of the coal seems not to influence the mechanical behavior of Illinois bituminous coals.

The geo-database of caprock quality and deep saline aquifers distribution for geological storage of CO 2 in Italy

One of the most promising options to stabilize and reduce the atmospheric concentration of greenhouse gases is Carbon Capture and Storage (CCS). This technique consists of separating CO 2 from other industrial flue gases and storing it in geological reservoirs, such as deep saline aquifers, depleted oil and/or gas fields, and unminable coal beds. A detailed reworking of all available Italian deep-drilling data was performed to identify potential storage reservoirs in deep saline aquifers. Data were organized into a GIS geo-database containing stratigraphic and fluid chemistry information as well as physiochemical characteristics of the geological formations. Caprock efficiency was evaluated via numerical parameterization of rock permeabilities, defining the “ Caprock Quality Factor” ( Fbp) for each well. The geo-database also includes strategic information such as the distribution of deep aquifers, seismogenic sources and areas, seismic events, Diffuse Degassing Structures, heat flow, thermal anomalies, and anthropogenic CO 2 sources. Results allow the definition of potentially suitable areas for future studies on CO 2 geological storage located in the fore-deep domains of the Alps and Apennines chains, where efficient marly-to-clayish caprocks lie above deep aquifers hosted in sands or limestones. Most of them are far form seismogenic sources and Diffuse Degassing Structures.

Preliminary assessment of CO2 geological storage potential in Chongqing, China

This paper presents a preliminary assessment of the potential for CO2 geological storage in Chongqing, China. Currently, there are about 116 large stationary CO2 point emission sources which emit 85.57 MtCO2/yr totally. These stationary sources are mainly belonged to four industries: cement, power plant, iron & steel and synthetic ammonia industries. In the three kinds of geological storage formations, namely, deep saline formations (DSFs), unmineable coalbeds and depleted gas fields, the total basin-scale theoretical storage capacities of CO2 reach 24.36 Gt, equivalent to about 285 times of the annual total CO2 emissions in Chongqing. The DSFs have the largest potential storage capacity accounting for 98% of the total storage capacities. The matching results between CO2 point emission sources and candidate geological storage formations show that 94.8% of the point emission sources (accounting for 97.1% of annual total emissions) can find at least one candidate geological storage formation in its adjacent areas. This means that, for Chongqing, the CO2 transport cost is likely very low. The research findings indicate that there is great potential for CO2 geological storage technology to deploy in Chongqing and for this technology to deliver profound and sustaining impacts on reducing CO2 emissions and developing low-carbon economy in Chongqing. This preliminary study is expected to stimulate more researches, critical thinking and policy actions to promote positive measures to reduce greenhouse gas emissions so as to mitigate the impact of global climate change, as well as to set a good example for other regions in China.

Coal swelling strain and permeability change with injecting liquid/supercritical CO2 and N2 at stress-constrained conditions

Abstract CO 2 sequestration in deep unmineable coalbeds is regarded as a viable option for carbon storage. On the other hand, many uncertainties still remain due to the fact that coal interacts with CO 2 in a variety of ways. In Japan, the first CO 2 Enhanced Coalbed Methane Recovery field trials at Yubari were carried out. CO 2 was injected from an injection well into a coalbed at a depth of 900 m, and coalbed methane was collected from an observation well. Since the CO 2 injection rate was an order of magnitude lower than that estimated by preliminary analyses, N 2 was injected in an attempt to improve it. However, this caused only a temporary increase in the CO 2 injection rate. To better understand the phenomena observed in the Yubari field tests, two laboratory experiments were conducted under stress-constrained conditions. In Test I, liquid CO 2 was injected into a water-saturated coal specimen and then heated and injected as supercritical CO 2 . This was to simulate the initial stage of CO 2 injection at Yubari when the coal seam was saturated with water. In Test II, supercritical CO 2 was injected into a coal specimen saturated with N 2 , and then N 2 and CO 2 were repeatedly injected. This test was to simulate the case of N 2 injection and CO 2 re-injection at Yubari. In Test I, a volumetric swelling strain of 0.25 to 0.5% was observed after injecting liquid CO 2 . However, in Test II, the swelling strain was about 0.5 to 0.8% after injecting supercritical CO 2 . Following further injection of N 2 in Test II, slow strain recovery was observed in the coal. At an effective stress of 2 MPa, the permeability of the water-saturated coal specimen was 2 × 10 − 6 darcy. In contrast, the permeability of the N 2 -saturated coal specimen was originally 5 × 10 − 4 to 9 × 10 − 4 darcy, and after injection of supercritical CO 2 it decreased to 2 × 10 − 4 darcy. Further injections of N 2 and supercritical CO 2 caused little subsequent change in permeability. These results suggest that when liquid CO 2 was injected into the water-saturated coal specimen, it did not completely displace the water in the coal matrix. To further investigate the coal swelling and permeability behavior during gas injection, elastic wave velocity measurements were carried out and the results were found to validate those obtained using strain gauges. The results indicate that coal swelling is likely to be the main cause for the permeability change in the Yubari field tests and thus provide useful information for modeling the field trial.

Analysis of the Storage Capacity for CO2 Sequestration of a Depleted Gas Condensate Reservoir and a Saline Aquifer

Summary Among the three types of geological CO2 sequestration (mature oil and gas fields, unminable coalbeds and deep saline formations), depleted gas condensate reservoirs are particularly interesting. First, because of the high-compressibility of gas, these reservoirs have larger storage capacity than oil reservoirs or aquifers. Second, the condensate that has dropped out from the gas phase during natural depletion will re-vaporize because of re-pressurization of the reservoir and by miscibility with the injected CO2. This condensate can be recovered from producing wells and leaves more pore volume for available storage of CO2. The objective of this study is to investigate the CO2 storage capacity in different formation types, for different levels of CO2 purity and different injection schedules. To this aim, we analyzed the injection of a CO2-based stream into a depleted gas condensate reservoir and into a saline aquifer using a compositional reservoir simulation model. The dynamics of the reservoir impose a minimum period of injection that is required in order for the storage scheme to benefit from 100% of the reservoir storage capacity. Hence, over and above a certain CO2 injection rate, it becomes meaningless to invest in bigger compressors to increase this rate to reduce the time of injection. When the CO2 stream contains impurities, such as N2 or methane, the storage capacity of the reservoir decreases proportionally to the impure stream's compressibility factor and its concentration of impurities. This finding suggests that an economic optimum between the costs of separation, compression and injection can be determined. Finally, the mass of CO2 sequestrated per pore volume in the equivalent aquifer model is approximately 13 times lower that of the depleted gas condensate reservoir model. This confirms that, because of their low overall compressibility, aquifers offer a far lower ratio of CO2 stored per pore volume than depleted gas condensate reservoirs. However, aquifers tend to have a far larger extent, which often compensates somewhat for this lower ratio and therefore provides storage for significant volumes of CO2.

Small-molecule gas sorption and diffusion in coal: Molecular simulation

Abstract Injections of carbon dioxide (CO2) into unmineable coalbeds can both enhance coalbed methane recovery (ECBM), a high-efficiency energy, and realize underground storage of CO2. In these processes, the diffusion and sorption of methane (CH4) and carbon dioxide are key dominant processes. In this study, the diffusion and sorption behavior of CH4 and CO2 in coal are investigated and compared based on molecular simulation. The calculated diffusion coefficient of CO2 was in the order of 10−9 m2/s, which is reasonably close to the experimental result. The sorption isotherms were obtained using the grand canonical Monte Carlo method. Coal tended to adsorb more CO2 than CH4 at a given temperature and pressure. The sorption heat of CO2 was larger than that of CH4 (7.9 and 5.8 kcal/mol respectively), accounting for the fact that the CH4 adsorbed in the coal seam could be replaced by CO2. This presents an alternative method for directly studying the interactions between coal macromolecule and small-molecule gases under various external environments.

Assessing the Water Uptake of Alberta Coal and the Impact of CO2 Injection with Low-Field NMR

Abstract Coal property characterization is an essential step to develop coalbed methane (CBM) recovery processes. In most cases, coal contains free water in the cleats (except dry coal), as well as moisture that forms an integral part of the coal structure. Most CBM production starts with dewatering coalbeds to initialize the gas recovery. Therefore, the wetting behaviour of coal by water is an important aspect in coal property studies. As CO2 has a strong affinity to coal, CO2 injection may change the coal wetting behaviour during a so-called enhanced coalbed methane process (ECBM). Studies on coal wettability are rare. This paper investigates the water uptake by Alberta coal and its wettability alteration due to CO2 injection using low-field nuclear magnetic resonance (NMR). Low-field NMR is a technique used in logging and in the analysis of fluids contained in reservoir rocks. It measures the hydrogen density in reservoir fluids and distinguishes between 'free' bulk water and 'bound' surface water. CO2 is invisible to NMR, but its impact can be detected by changes in the water signal. Experiments on coal samples in the form of dry and moist powder and chunk are used. The water uptake rate can be shown by monitoring the geometrical mean transverse relaxation time. From the spectra of different coal samples, water can be characterized into free, capillary-bound and subsurface-bound (adsorbed) water. These forms of water have different uptake behaviour inside coal. The injection of CO2 will cause coal dewatering, and the effect will increase with elevated CO2 pressure. Introduction Coalbed methane (CBM) has evolved into a commercially profitable source of unconventional natural gas. Canada has vast resources of coal and it has been estimated that the total in-place reserves are 36 ? 1012 m3. Over 60% of Canada's CBM resource is in Alberta(1). Coalbed methane has the potential of contributing a significant portion of Canadian natural gas production in the foreseen future. Using CO2 to enhance methane recovery has been discussed by several researchers(2, 3). This process is called CO2-ECBM. If successful, its implications include CO2 sequestration in deep unmineable coalbeds. Coal property characterization is an essential step to develop CBM/ECBM recovery processes. In most cases, coal is wet and contains free water in the cleats, as well as moisture that forms an integral part of the coal structure. Some coals found in the Western Canadian Sedimentary Basin's Horseshoe Canyon Formation are dry coals, which means the coal cleats no longer preserve free water. Most CBM production starts with dewatering coalbeds to initialize gas recovery. Therefore, the wetting behaviour of coal by water is an important aspect in coal property studies. As CO2 has a strong affinity to coal, CO2 injection may change the coal wetting behaviour in the ECBM process. Published studies on coal wettability are very rare to the best of our knowledge. Low-field NMR is a relatively new technique used in logging and in the analysis of fluids contained in reservoir rocks.

The CO2 Capture Project Phase 2 (CCP2) Storage Program: Progress in Geological Assurance in Unmineable Coal Beds

Abstract The CO 2 Capture Project’s (CCP) Phase 2 program made significant progress addressing issues to facilitate assurance of the safety and security of geological storage of CO 2 . This work included stakeholder assurance of CO 2 storage in unmineable coal beds. Simulation studies of CO 2 injection into coal beds were designed to identify operating conditions that will minimize leakage of CO 2 and maximize production of methane. Geophysical models were used to simulate gravity and electromagnetic responses from coal beds containing CO 2 . Hyperspectral remote sensing was evaluated for its ability to detect leakage of CO 2 and CH 4 to the surface.

耐ＣＯ２セメントテクノロジー

CO2 resistant cement-zonal isolation technology dedicated to CO2 geological storage-provides an enduring solution to reducing well leakage risks in carbon capture and storage (CCS) and CO2 enhanced oil recovery (EOR) projects.CCS involves capturing CO2 from the major sources of concentrated emissions and injecting it into selected geological formations such as saline aquifers, depleted hydrocarbon reservoirs and unminable coal beds. CCS has the potential to make a critical contribution to reducing the amount of greenhouse gas released into the atmosphere as the most effective, safe, and low-cost long-term CO2 storage technology.One of the key requirements in CCS is long-term zonal isolation. Subsurface pressure and temperature changes can compromise the stability and integrity of the cement sheath around a CO2 injection well. Compromising well integrity can quickly lead to CO2 leakage at the surface, putting containment at risk. That's why the cement sheath used in the wellbore must be exceptionally durable and able to maintain its integrity for hundreds of years.Portland cement has been used successfully for decades in oil and gas well cementing. However, such cements are thermodynamically unstable in CO2-rich environments and degrade once exposed to CO2 in the presence of water. For this reason, compromised well integrity has been identified as the greatest risk factor for leakage from underground storage sites.CO2-resistant cement ensures lasting zonal isolation. In laboratory tests, the system proved highly resistant to CO2 attack, maintaining stable mechanical properties after exposure to simulated extreme injection/storage downhole conditions, including wet supercritical CO2 and water saturated with CO2. This cement system is 100% compatible with Portland cement and can be blended, mixed, and pumped using standard field equipment. It can be used for zonal isolation in new CO2 injection wells, or to plug and abandon existing CO2 injection/production wells at the end of a project.

Economic analysis of carbon dioxide sequestration in powder river basin coal

Unminable coalbeds are potentially large storage reservoirs for the sequestration of anthropogenic CO 2 and offer the benefit of enhanced methane production, which can offset some of the costs associated with CO 2 sequestration. The objective of this paper is to study the economic feasibility of CO 2 sequestration in unminable coal seams in the Powder River Basin of Wyoming. Economic analyses of CO 2 injection options are compared. Results show that injecting flue gas to recover methane from CBM fields is marginally economical; however, this method will not significantly contribute to the need to sequester large quantities of CO 2 . Separating CO 2 from flue gas and injecting it into the unminable coal zones of the Powder River Basin seam is currently uneconomical, but can effectively sequester over 86,000 tons (78,200 Mg) of CO 2 per acre while recovering methane to offset costs. The cost to separate CO 2 from flue gas was identified as the major cost driver associated with CO 2 sequestration in unminable coal seams. Improvements in separations technology alone are unlikely to drive costs low enough for CO 2 sequestration in unminable coal seams in the Powder River Basin to become economically viable. Breakthroughs in separations technology could aid the economics, but in the Powder River Basin they cannot achieve the necessary cost reductions for breakeven economics without incentives.