Research progress of coal seam gas content determination technology and equipment

Abstract

Gas content is an important parameter for the prediction of coal and gas outburst risk, the estimation of coal seam gas resource, and the design of mine gas control engineering. Focusing on how to accurately and quickly determine the gas content of coal seams in large area, and relying on the National Science and Technology Major Project, the National Natural Science Foundation of China, the Joint Fund of Coal Enterprises and other projects to develop scientific and technological research, some progress had been made in sampling and testing, and the main manifestations were as follows. ① The development of sampling for gas content determination in coal seam has gone through four stages, namely, orifice sampling, core tube spot sampling, pressure injection spot sampling, and sealed sampling. The pressure holding capacity of the sealed sampling equipment reached 11.5 MPa, and the diameter of coal core reached 38 mm. ② According to different geological conditions of coal seams, three types of sampling techniques had been developed, including directional long borehole sealed sampling along coal seam, floor cross-layer borehole sealed sampling, and comb-shaped directional long borehole sealed sampling in roof or floor. ③ In the hard coal seams of Jiaozuo mining area in Henan Province and Jincheng mining area in Shanxi Province, the sampling depth of the directional long borehole along the seam reached 516 m, and the gas content of the coal seam measured by the sealed sampling method was increased by an average of 0.44 and 1.04 times compared with the conventional sampling method, respectively. In the broken soft coal seam of the Huainan mining area in Anhui Province, the sealed sampling depth of the cross-layer borehole reached 209 m, and the measured gas content of the coal seam was increased by 0.26 times on average compared with the conventional sampling method. In the broken soft coal seam of the Huaibei mining area in Anhui Province, the comb drilling sealed sampling depth reached 484 m in roof or floor, and the measured coal seam gas content was 0.19 times higher than that of the conventional sampling method. The sealed sampling method was superior than the conventional sampling method in terms of determination accuracy and detection range of coal seam gas content. ④ In terms of gas content testing, in addition to the traditional natural desorption test, a series of coal mine gas content rapid test equipment had been developed, which can measure the gas content of coal seam within 30 min at the earliest, and was generally used for gas content testing in 100-meter hole. It is proposed that the sealed sampling equipment for coal seam gas content determination needs to be developed in the direction of miniaturization and lightweight, and it can realize sealed sampling with the drilling. In the test, a reasonable desorption termination limit should be determined according to the actual situation, and the testing equipment and sealed sampling equipment should be further combined to achieve the rapid and accurate determination of gas content in deep hole. Sealed sampling technology has become the main means of accurate exploration and prediction of coal seam gas content in large areas, and it is an important technical guarantee for the safe and efficient coal mining.

Keywords

• coal seam gas content
• fixed-point sampling
• sealed sampling
• broken soft coal seam
• hard coal seam