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• In FTIR and mercury intrusion study of molecular structure change characteristics of SDS modified coal. • Correlation of coal molecular structure with wettability and methane adsorption capacity. • Essence to the explanation of the decrease of coal methane adsorption capacity under SDS modification coal. Adding ionic solution can improve the microstructure of coal, inhibit the gas absorption capacity and effectively reduce the outburst risk. In this paper, the high-quality anthracite in Jincheng, Shanxi Province is selected as the research object, and sodium dodecyl sulfate (SDS) ion solutions with different concentrations are configured. Combined with infrared spectroscopy, mercury intrusion test, the change features of coal microstructure after soak by SDS solutions with different concentrations are studied, and the variations of the contact angle and adsorption constant of samples before and after modification are tested. The paper further discusses the influence of changing coal microstructure on the wettability and gas adsorption. The experimental results show that SDS can modify the microstructure of coal to some extent: –OH, -C O, and C O C increase obviously, macropores and mesopores increase, micropores and ascospores decrease. After SDS modification, the contact angle and the maximum gas adsorption a decrease linearly as oxygen groups and vtotal increase. In addition, the hydrophilic groups in the coal body increase significantly, which makes it easier to attract water molecules, and strengthen the pore connectivity and coal wettability. The polar oxygen-containing functional group molecules of coal also increase, occupying the adsorption site of non-polar molecular methane, and the adsorption site (micropore) decreases. The conclusion of this paper establishes theoretical foundation for the exploitation of coal seam gas resources. Adding SDS can directionally ameliorate coal microstructure, and then regulate the coal wettability and its ability to adsorb methane, to utilize coal resources safely and efficiently. [ABSTRACT FROM AUTHOR]

Abstract: Deviated well is one of the main well types to develop coalbed methane in China. It's been widely used by various coalbed methane companies in recent years. Compared with traditional oil and gas wells, coalbed methane wells are characterized by shallow depth and strict well spacing, which means higher wellbore quality control technology. Furthermore, coalbed methane wells are apt to produce coal dust during dewatering and coal dust causes serious abrasion of pipe and rod. It's required to improve wellbore quality. This paper analyzes the weakness of current wellbore quality control standard and technology for coalbed methane wells on the basis of the characterization of coaled methane wells and finds out the key factors that control wellbore quality of coalbed methane deviated wells. The technology is developed to improve wellbore quality of coalbed methane wells from trajectory design and real-time control. Through the on-site test in Baode block, Shanxi Province, the technology is further improved and it's confirmed by the test result that this technology can improve the wellbore quality of coalbed methane deviated wells. In addition, this paper also presents some good suggestions for compiling standard about wellbore quality control for coalbed methane deviated wells. [Copyright &y& Elsevier]

The identification of sedimentary facies and their lithological distribution characteristics is very important for exploration and development of coalbed methane (CBM). However, the thin interlayer that is common in coal-bearing formation, makes it difficult to predict the favorable facies zone of high frequency sequences based on the conventional methods. In this paper, a seismic sedimentology method was founded to reveal the sedimentary microfacies of high frequency sequences in the coal-bearing Shanxi Formation of the Zhongyu area in the central-western of the Qinshui Basin. The first step of this method is the selection of equal-scale stratal slices and extraction of seismic attributes, then several useable seismic attributes were optimized from all seismic attributes based on the relationship between the seismic attributes and net-to-gross ratios of several single-wells, and finally a model was established to depict the spatial distribution characteristics of sedimentary bodies. Results show that the sedimentary environment of SQ8 and SQ9 in Shanxi Formation is lower delta plain and the upper delta plain respectively. Moreover, the distribution characteristics of net-to-gross ratio across the study area were predicted based on the provided seismic sedimentology. Subsequently, the relationship between the net-to-gross ratio and CBM content of several sing-wells was used to predict the CBM gas content in the study area. The results show that the CBM gas content of No. 2 coal seam ranges from 5 to 20 m3/t, and it decreases with the increase of the net-to-gross ratio in SQ8 and SQ9. The relative error for the predicated gas content results ranges from −14.48% to 3.94%, indicating that the method is effective. Finally, based on the distribution of CBM gas content, the study area is divided into four types, in which the muddy sediment control area (Type IV, located in the central and eastern parts of the study area) is the most favorable for CBM preservation. This study provides a methodology to predict the sedimentary microfacies and CBM gas content in the coal-bearing strata, which extends the application of seismic sedimentology in coal and CBM geology. • First attempt of the predicating coalbed methane content by seismic sedimentology. • Pioneer research of coalbed methane geology in Zhongyu area of the Qinshui Basin. • Application of seismic sedimentology in coal-bearing formation evaluation. • Identification of sedimentary microfacies in coal-bearing strata by seismic attributes analysis. • Extend the application of seismic sedimentology in coal and coalbed methane geology. [ABSTRACT FROM AUTHOR]