Geoff Wang

Numerical description of coalbed methane desorption stages based on isothermal adsorption experiment

Quantitative description of desorption stages of coalbed methane is an important basis to objectively understand the production of coalbed methane well, to diagnose the production state, and to optimize the management of draining and collection of coalbed methane. A series of isothermal adsorption experiments were carried out with 12 anthracite samples from 6 coalbed methane wells located in the south of the Qinshui Basin, based on the results of isothermal adsorption experiments, and an analytical model was developed based on the Langmuir sorption theory. With the model, a numerical method that adopts equivalent desorption rate and its curve was established, which can be used to characterize the staged desorption of coalbed methane. According to the experimental and numerical characterizations, three key pressure points determined by the equivalent desorption rate curvature that defines pressure-declining desorption stage, have been proposed and confirmed, namely, start-up pressure, transition pressure and sensitive pressure. By using these three key pressure points, the process of coalbed methane desorption associated with isothermal adsorption experiments can be divided into four stages, i.e., zero desorption stage, slow desorption stage, transition desorption stage, and sensitive desorption stage. According to analogy analysis, there are differences and similarities between the processes of coalbed methane desorption identified by isothermal adsorption experiments and observed in gas production. Moreover, it has been found that larger Langmuir volume and ratio of Langmuir constants are beneficial to earlier advent of steady production stage, whereas it is also possible that the declining production stage may occur ahead of schedule.

Nano‐ and Microscale Engineering of the Molybdenum Disulfide‐Based Catalysts for Syngas to Ethanol Conversion

Nickel‐promoted MoS2, unsupported catalysts and laponite‐supported alcohol synthesis catalysts were synthesised by using microemulsion (ME) and hydrothermal (HT) methods. Highly ordered sulfide slabs, consisting of up to seven layers, were visible in the TEM images of HT‐based NiMoS2 catalysts. In contrast, disordered sulfide layers were identified in ME‐based NiMoS2 catalysts. High catalytic activity was observed in ME‐based supported (laponite‐supported NiMoS2) and unsupported catalysts. After the CO hydrogenation reaction, the catalysts were characterised by X‐ray photoelectron spectroscopy and inductively coupled plasma–mass spectrometry elemental analyses, which detected a significant sulfur loss in ME‐based NiMoS2 catalysts and minor sulfur loss in HT‐based NiMoS2 catalysts. In addition to the large surface area (120 m2 g−1), disordered sulfide structure, and exposed active sites, ME‐based NiMoS2 catalysts demonstrated higher alcohol selectivity (61 mol %) than HT‐based NiMoS2 catalysts (15 mol %). Correlations between the catalyst morphology, surface active components, and alcohol selectivity are discussed herein.

Vertical Diversity of Coalbed Methane Content and its Geological Controls in the Qingshan Syncline, Western Guizhou Province, China

The distribution of methane content in the coalbed is complex in the Qinshan Syncline of western Guizhou Province. Analyses of factors controlling on the distribution of gas content are made in this paper. Coal ranks and geo-structure in the region showed strong controls on the gas distribution. Coals with higher degree of metamorphism or located in syncline most likely have higher gas content. With the concept of coalbed methane content unite thickness (CBMCUT), those factors such as coal seam buried depth and coal structure present positive relations with gas content. Results indicated that the variation of CBMCUT is not fixed in different research areas or in different coal structures. Namely, the variation follows “v-shaped” correlation with the increasing coal buried depth in the region of Qinshan Syncline. However, the trend is smooth for the coals in the Panzhuang mining area. Usually, the critical value for primary-texture coal and mylonitized is different based on the analysis of the relationship between coal structure and CBMCUT in those two areas described above. The value is commonly higher in mylonitized coal and lower in those mainly primary-texture and fragmented coals.

Investigation on coal seam gas formation of multi-coalbed reservoir in Bide-Santang Basin Southwest China

This paper presents a comprehensive study on the geological characteristics of a multi-coalbed reservoir using coal cores collected from well drilling tests in Bide-Santang Basin, China. The study focuses on the investigation of the coalbed methane (CBM)-bearing property, porosity and permeability, sealability of capping rocks, and groundwater characteristics in coal seams, providing the experimental information on the control function of sequence strata for the coalbed methane. This reservoir is comprised of a large number of coalbeds and exhibits many distinctive geological characteristics of a CBM reservoir, such as high CBM content, complex vertical volatility of CBM content, vertical discontinuous distribution of porosity and permeability, strong sealing capping property and many vertical water-bearing systems, etc. The investigation shows that the unattached multiple superposed CBM-bearing system (UMSCS), which formed the unique multi-coalbed CBM reservoir, can be identified in the study area. Depending on the development scale of vertically unattached CBM-bearing coal seams, the CBM reservoir in the study area can be classified as simple UMSCS and complex UMSCS. The former, typically appearing in Zhuzang syncline and Agong syncline, exhibits the continuity of geological reservoir-forming characteristics in terms of less coal seams, much weaker sealability of capping rocks, higher CBM content, and many vertical water-bearing systems. The latter, typically represented by Shuigonghe syncline and Santang syncline, shows the continuity of geological reservoir-forming characteristics with a large number of coal seams, strong sealing capping property, and reasonably high CBM content. For simple UMSCS reservoirs, a sublevel exploitation method should be adopted for CBM exploitation in order to minimize the effect caused by larger variation of the reservoir energy in different systems. For complex UMSCS reservoirs, one effective way for CBM exploitation is to fracture virtual reservoir (mainly key sandstone member) to depressurize it uniformly and thus achieve large-scale discharging and mining in several adjacent CBM-bearing subsystems.

A gas mixture enhanced coalbed methane recovery technology applied to underground coal mines

This paper presents a field trial for developing a gas mixture enhanced coalbed methane (GECBM) technology that can be integrated with underground coal mine methane (CMM) drainage systems. The field trial was carried out in a deep underground coalmine roadway in two stages, initially degassing using a conventional method for 30 days in three boreholes installed in the underground coal seam and then injecting the gas mixture from one of the boreholes for about 2 months. The field trial focuses on the investigation of the technical and economic feasibilities of G-ECBM technology applied to underground CMM drainage systems. The results revealed that the G-ECBM technology integrated with underground methane drainage systems can provide an effective method to enhance the coalbed methane (CBM) recovery from coal mines and the efficiency of underground gas drainage systems, and hence improve the mining safety. The field measurements showed that the single-borehole flow rate and concentration of CH4 for the production boreholes with G-ECBM have increased by a factor of 4.73 and 1.68 on average, respectively, compared with the conventional production boreholes without G-ECBM. The results also showed the economic prospect of applying G-ECBM technology to underground CMM drainage systems.

Coalbed methane resources and reservoir characteristics of NO. II1 coal seam in the Jiaozuo coalfield, China

Jiaozuo coalfield is located in the northwest of Henan province, China, and close to the Southern Qinshui coal basin, the most successfully commercial CBM resource developed area in China. The No. II1 coal seam is the main economic coal seam in Jiaozuo coalfield and its average thickness exceeds 5.36m. The maximum reflectance of vitrinite (RO,max) of the No. II1 coal across the Jiaozuo is between 3.16% and 4.78%. The coalbody structure of the No. II1 coal seam changes greatly in different part and can be generally divided into 1∼3 sub-layers. The micropores in the No.II1 coal seam is the major pores, secondly are transitional pores, and then less macropores and mesopores. The No. II1 coal seam has stronger adsorption, and the reservoir natural permeability has an evident heterogeneity vary from 0.0001 to 83.71mD. High permeability region is often near fault structure or the boundary of fault block. The CBM genetic type is homologous thermal cracking gas of humic coal with high matunity. Gas content with the burial depth of 163∼1070m varies very greatly from 4.65 to 45.75m3/t, with an average value of 18.3m3/t, and gradually increases from northeast to southwest. According to the latest evaluation for CBM resource in Jiaozuo coalfield, the existing total in-place CBM resources in the No. II1 coal seam with the depth of shallower than 2000 m are close to 1.2 × 1012m3, most of them mainly distribute in the depth of 1000 ∼ 1500 m. The existing total in-place CBM resources is dominated by the inferred CBM resource reserves (more than 70%), which distribute the undrilled places with few coal geological knowledge and deeper than 1000m. The resource concentration of the No. II1 coal seam in Jiaozuo coalfield is in the range of (0.513–3.478)x108 m3/km2, with an average value of 1.805×108 m3/km2. Based on the CBM resource investigation and reservoir evaluation, the most prospective target zones for CBM production in Jiaozuo coalfield include Guhanshan coal mine, Jiulishan coal mine and the west part of Qiangnan coal district.

Oxidation mechanism of Si3N4-bonded SiC ceramics by CO, CO2 and steam

This paper presents a theoretical and experimental investigation into the oxidation reactions of Si3N4-bonded SiC ceramics. Such ceramics which contain a small amount of silicon offer increased oxidation and wear resistance and are widely used as lining refractories in blast furnaces. The thermodynamics of oxidation reactions were studied using the JANAF tables. The weight gain was measured using a thermogravimetric analysis technique to study the kinetics. The temperature range of oxidation measurements is from 1073 to 1573 K and the oxidation atmosphere is water vapour, pure CO and CO–CO2 gas mixtures with various CO-to-CO2 ratios. Thermodynamic simulations showed that the oxidation mechanism of Si3N4-bonded SiC ceramics is passive oxidation and all components contribute to the formation of a silica film. The activated energies of the reactions follow the sequence Si3N4>SiC>Si. The kinetic study revealed that the oxidation of Si3N4-bonded SiC ceramics occurred in a mixed regime controlled by both interface reaction and diffusion through the silica film. Under the atmosphere conditions prevailing in the blast furnace, this ceramic is predicted to be passively oxidized with the chemical reaction rate becoming more dominant as the CO concentration increases.

Experimental and numerical simulation of discrete liquid flow in a packed bed

This paper presents a combined experimental and numerical method to simulate the liquid flow in a packed bed. Two types of the experiments, i.e. liquid percolation without gas flow and liquid flow with gas cross flow, were conducted using a three- or two-dimensional cold model, respectively. A mathematical model has been proposed for the numerical simulation of the liquid flow. This model was developed using a force balance approach combined with stochastic considerations, in which the liquid flow was treated as a discrete phase with stochastic dispersion based on the experimental observations. Accordingly, the interactions between liquid and the packed bed, and liquid and gas have been experimentally investigated and then were used to determine the model parameters involved in the model. The behavior of the liquid flow in packed beds can numerically be simulated using the proposed model. A reasonable agreement has been achieved between the model predictions and the experimental measurements.

Resources and geology of coalbed methane in China: a review

ABSTRACT China produced 17.1 billion cubic meters (BCM) of methane sourced from coal seams in 2015, of which 4.43 BCM is from wells drilled from the surface. This level of production is a clear indicator that China has gone into early stage large-scale coalbed methane (CBM) development. CBM resources in China have been extensively investigated since the 1980s. Research has focused on the geological controls of reservoir character. There have been significant advances over the last 37 years that have aided China’s CBM industry. CBM resources less than 2000 m in depth in China are estimated to be 36.81 trillion cubic meters, of which more than 84% occur in nine large-scale basins, such as the Qinshui, Ordos, Junggar, Qianxi, Erenhot, and Hailar. CBM accumulation and coal reservoir characteristics are controlled by the deposition, structure, coal rank, hydrology as well as other geological factors. Each basin has its own unique geological controls that influence the character of CBM reservoirs in both subtle and obvious ways. Coal reservoir geology in some basins or regions in China are still not well understood because of the complexity of the geological settings. At present, large-scale CBM production in China only occurs within the Qinshui and Ordos basins, mostly sourced from middle-to-high rank coal reservoirs. The CBM geology in other basins needs further investigation in order to achieve large-scale commercial production. To this end, the geological research in the paper should address issues such as how to stimulate economic gas flow from deep low permeability reservoirs and how best to efficiently produce from multiple horizons simultaneously. This paper summarizes these and other key issues that are significant scientific and technical challenges for the CBM industry within China.

Investigation on pore structures of a medium volatile bituminous coal with solvent extraction tests

This paper presents an experimental investigation on the changes of pore structures, pore morphology of a medium volatile bituminous coal through solvent extraction under ultrasonic irradiation. The solvent extraction experiments, carried out using four non- or weak-polarity solvents with the twice- and thorough-extraction methods, provided a series of extract residues for comparison study on the coal pore structure with reference to the coal sample. Scanning electronic microscopy (SEM) and mercury injection porosimetry (MIP) were used to study the morphological and structural changes of pores both the coal samples and the residues. The results show that most solvable organic components can be extracted from coal through twice-extraction method with the solvents used in this study; under the ultrasonic irradiation, the solvent extraction makes the surfaces of coal particles grow loose and thus come to pieces forming many intergranular pores. And the numbers of intergranular pores have a tendency to increase as the extraction degree increases; the solvent extraction produced the “pore expansion” effect and increased opening pores, and hence can improve the connectivity among pores and make the pore distribution more uniform.