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Geological sequestration of carbon dioxide (CO2) is an effective method to reduce greenhouse gases and an important technology for carbon neutralization. Among all geological sequestration sites, coal reservoirs are potentially effective and practicable. The Xiangzhong Depression of Hunan Province of China is selected as the research area, and the coal seam of Longtan Formation is the target reservoir in this paper. CO2‐enhanced coalbed methane (CO2‐ECBM) and CO2 sequestration capacity are both simulated according to the laboratory experiments on reservoir parameters. During simulation, four production wells and one injection well were designed, and the simulation process can be divided into two stages: CO2‐ECBM and CO2 geological storage. The CO2‐ECBM stage refers to CO2 injection for increasing methane production, and the CO2 geological storage stage aims to predict the CO2 sequestration capacity. After that, sensitivity analyses of sequestration effect are carried out. During the simulation, when maintaining a constant pressure injection of CO2 under the original conditions of 0.01 mD permeability, 9% porosity, and 1.47 MPa reservoir methane pressure, the total storage amount is only 0.14 × 106 m3. However, the storage amount increases significantly to 6.62 × 106 m3 if the permeability increases to 1.5 mD. Orthogonal simulation indicates that permeability has the greatest impact on CO2 sequestration. © 2024 Society of Chemical Industry and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

As coal pore development is decisive for choosing the engineering site and predicting the CO2 storage capacity, this paper provides a new method to define the double T2 cutoff values by using cumulative amplitude ratio measured by nuclear magnetic resonance measurements, classifies the coal pore systems, and analyzes the influences on cumulative amplitude ratio. The following cognitions are achieved. The minimum ratio always varies narrowly and ranges from 0.9 to 1.1, which is quite stable and approximately equals to 1. Ranges of maximum and average ratios are 1.2–3.5 and 1.1–1.8, respectively. T2c1 represents the dividing point of diffusion pore and permeation pore, and its average value is about 4.1 ms. T2c2 represents the dividing point of permeation pore and cleat, with an average value of about 81.9 ms. The volumetric proportions of diffusion pore range from 1.5% to 76.2%, with an average value of 34.6%; the volumetric proportions of permeation pore are from 14.9% to 98.5%, with an average of 46.8%; while the volumetric proportions of cleat are between 8.4% and 57.5%, with an average of 26.6%. According to the different influencing degrees on maximum and average ratios, three types of parameters can be divided. The first type is strong correlation parameters and includes permeability, volumetric percentage of cleat, and relative volumetric percentage of cleat. The second type is medium correlation parameters, such as volumetric percentage of diffusion pore. The third type is weak correlation parameters, including T2 cutoff values, porosity, and maximum vitrinite reflectance. © 2023 Society of Chemical Industry and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In recent decades, coated ceramsite has become popular due to its low density, high compressive strength, and high flow conductivity, and it has been applied in many areas in construction field and chemical industry. In the area of hydraulic fracture, limited relevant literature can be found, especially on unconventional reservoirs with soft coals. In this paper, numerical simulation is performed to obtain migration regularity and granularity proportion using coated ceramsite, and it indicates that the biggest proppant concentration and strongest flow conductivity can be achieved under the granularity proportion of 1:6:2 with respective coated ceramsites of 40/60, 16/40, and 12/20 mesh. Then, a series of construction parameters are calculated and optimized to receive a best fracture performance by using mathematical methods, including total proppant volume, each proppant volume, fluid injection rate, fluid injection volume, and proppant concentration, etc. Results from micro seismic monitoring indicate that the actual fracture performance matches well with the simulated performance by using coated ceramsite and has an obviously longer fracture length and a bigger proppant concentration compared with performances by using quartz sand. Meanwhile, comparisons for gas productions fractured by coated ceramsite and quartz sand reveal that coated ceramsite can achieve a better drainage performance. All of the above can be a guide for hydraulic fracture and useful for enhancing coalbed methane recovery. © 2022 Society of Chemical Industry and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: The uranium deposits in the Tuanyushan area of northern Qaidam Basin commonly occur in coal‐bearing series. To decipher the U‐enrichment mechanism and controlling factors in this area, a database of 72 drill cores, including 56 well‐logs and 3 sampling wells, was examined for sedimentology and geochemistry in relation to uranium concentrations. The results show that coal‐bearing series can influence uranium mineralization from two aspects, i.e., spatial distribution and dynamic control. Five types of uranium‐bearing rocks are recognized, mainly occurring in the braided river and braided delta sedimentary facies, among which sandstones near the coals are the most important. The lithological associations of sandstone‐type uranium deposits can be classified into three subtypes, termed as U‐coal type, coal‐U‐coal type, and coal‐U type, respectively. The coal and fine siliciclastic rocks in the coal‐bearing series confined the U‐rich fluid flow and uranium accumulation in the sandstone near them. Thus, the coal‐bearing series can provide good accommodations for uranium mineralization. Coals and organic matters in the coal‐bearing series may have served as reducing agents and absorbing barriers. Methane is deemed to be the main acidolysis hydrocarbon in the U‐bearing beds, which shows a positive correlation with U‐content in the sandstones in the coal‐bearing series. Additionally, the δ13C in the carbonate cements of the U‐bearing sandstones indicates that the organic matters, associated with the coal around the sandstones, were involved in the carbonation, one important component of alteration in the Tuanyushan area. Recognition of the dual control of coal‐bearing series on the uranium mineralization is significant for the development of coal circular economy, environmental protection during coal utilization and the security of national rare metal resources. [ABSTRACT FROM AUTHOR]