Search

The import risks confronting gas consumers are influenced by, among other factors, geopolitics, transport conditions, and gas prices. Given the increase in China's natural gas imports (NGIs), evaluating the influence of natural gas import risks (NGIRs) on the national economy is necessary. First, China's NGIRs are quantified by considering country, transport and dependence risks. Second, this paper uses a co-integration model to explore the relationship between NGIRs and natural gas import costs (NGICs). Third, an input-output analysis is used to analyse the influence of NGICs on the national economy. The results show that the corresponding impact on gross domestic product (GDP) is 2305.2 million Yuan, assuming a 10% increase in China's NGIRs. The impact of NGIRs differs across domestic sectors; the oil & gas extraction (S3) and gas production and supply (S24) sectors are the most heavily affected. Finally, some suggestions are proposed to improve China's long-term natural gas import security such as improving early warning services for maritime disaster risks. [ABSTRACT FROM AUTHOR]

Over past decades, China has changed the manner in which coal mine methane (CMM) was treated: from mitigating its dangers as a mining hazard to developing its potential as an unconventional gas resource. CMM is rich in China coal seams. These coal seams normally have three distinct characteristics: high pressure, strong adsorption and low permeability. These characteristics require novel extraction and utilization technologies. This paper presented a comprehensive review of how these technologies evolve with time from underground extraction to surface drainage to combined surface-underground approach. Major conclusions include: (1) CMM is mainly drained through underground extraction technologies. In order to improve the drainage efficiency, these technologies usually combine with mining-induced stress relief or other active stimulation techniques and modern borehole sealing techniques; (2) Several innovative surface CMM extraction technologies have been proved as effective for Chinese CMM formation conditions, such as gob surface well extraction, stress-relieved seams surface well extraction, multi-branch horizontal directional surface well extraction, and multipurpose surface well extraction; (3) A combined surface-underground approach has been applied to Huainan and Jincheng coal mines. These applications represent the new development trend of CMM extraction and control in China; and (4) Apart from the CMM extraction technologies, utilization technologies also achieved significant progresses in China. The electricity generation and safe transportation technologies of low-concentration gas have also been developed to improve the gas utilization rate and guarantee the safe long distance and large flow transportation of low-concentration gas in China. The implementation of CMM extraction and utilization technologies has led to a large increase of coal production, gas extraction and utilization, and a significant reduction of fatality. [ABSTRACT FROM AUTHOR]

Gas injection into coal seams is gaining increasing attention for improving coalbed methane (CBM) production. This technical development requires detailed and reliable information on gas adsorption/desorption-induced deformation and gas occurrence mechanisms. Hence, in this paper, high volatile bituminous coal was taken as the experiment samples from northern Shannxi Province, China, and adsorption-induced swelling experiments with CO 2 and N 2 were carried out under the conditions of one-time injection and step-by-step injection. Then, based on adsorption-induced swelling characteristics, a thermodynamic model was further established to disclose the adsorption/desorption-induced deformation mechanism of confined coals. Results showed that the swelling/shrinkage strain curves of CO 2 and N 2 adsorption/desorption in the coal matrix were generally divided into four stages, including pressurization-deformation, adsorption-induced swelling, depressurization-deformation, and finally desorption-induced shrinkage. It can be seen that the coal swelling effect caused by N 2 adsorption was far less than that caused by CO 2 adsorption. However, both CO 2 and N 2 adsorption displayed that the apparent volumetric swelling weakened with increasing strain when compared with the same adsorption pressure under different strain conditions. In contrast, the absolute volumetric swelling of the confined coal was a coupling result from adsorption-induced swelling and pore pressure effects. Further, based on the thermodynamic model, it was verified that the adsorbate type, the chemical potential of the adsorbate molecule and stress conditions are key factors affecting adsorption-induced swelling of coal under a certain temperature and pressure. In addition, a desorption lag phenomenon during the desorption-induced shrinkage stage was observed, due to incomplete gas desorption and gas retention in the coal macromolecular network. It was also found that there was a shrinkage phenomenon after the peak strain during gas adsorption. That is to say, when fixed adsorption sites on the coal pore surface reached the adsorption saturation state at the peak strain, gas molecules would be stored in an absorption state in the coal macromolecular network under continuous adsorption. These phenomena further explained coal swelling and gas occurrence mechanisms. • Swelling/shrinkage strain curve can be generally divided into four stages. • Absolute volumetric swelling is controlled by adsorption swelling and pore pressure. • Thermodynamic model reflects Gibbs free energy of gas adsorption in coal decreases. • Adsorption-induced swelling effect tends to be dropped with increasing stress. • Shrinkage effect after peak strain and desorption lag are occurred in whole process. [ABSTRACT FROM AUTHOR]

Hydraulic fracturing can increase coal seam fractures and reduce gas outburst risks, but the main challenge of its implementation in coal mines is to achieve uniform fracturing and gas reduction. In this paper, we studied the mechanism of water-driven gas release through two aspects: the H 2 O molecule is more easily adsorbed by coal than CH 4 , and water can decrease the gas adsorption capacity of coal. Comparative experiments of conventional hydraulic fracturing and blasting-fracturing technologies were carried out in #8 coal mine in Pingdingshan, China. We found that fractures and water contents around the blasting-based fracturing hole were more uniform than the conventional fracturing hole. After hydraulic fracturing, low water content coal usually has high gas content, which confirmed that gas in wet areas was displaced by water and driven to dry areas. To improve the uniformity of hydraulic fracturing, we proposed the uniform fracturing technology by combining blasting-fracturing holes and control holes. Blasting before hydraulic fracturing will increase the uniformity of fracturing and water distribution, and the control holes are used to monitor and release gas driven by water injection. The effective wetting range of conventional hydraulic fracturing was from −6 to 6 m along the strike direction and from −3 to 9 m along the dip direction with 94.71 m3 water injected. While the effective wetting range using uniform fracturing was increased to from −21 to 18 m along the strike direction and from −12 to 18 m along the dip direction with78.13 m3 water injected. Furthermore, number of boreholes to be drilled was largely reduced from 1300 to 132 when using the uniform fracturing technology to replace the dense hole technology in a 300 m long roadway. This research has suggested that uniform fracturing can effectively reduce gas outburst risk in gassy mines in China. • Analyzed water-driven gas release mechanism for coal and gas outburst control. • Developed uniform hydraulic fracturing by blasting and water-driven gas release. • Demonstrated uniform fracturing in field trails with less borehole required and less outburst risk. [ABSTRACT FROM AUTHOR]