Determination of Key Technical Parameters in the Study of New Pressure Sealing Technology for Coal Seam Gas Extraction

Abstract

Coal is affected by the concentrated stress disturbance of mining, the disturbance of drilling hole formation, and the concentrated stress of coal shrinkage and splitting of gas desorption from the hole wall; these result in a large number of secondary cracks that collect and leak gas. As a result, it is difficult for the coal seam sealing process to meet engineering quality sealing requirements, which results in problems such as low gas concentration during the extraction process. In this paper, based on the analysis of coal pore and fissure characteristics, and in view of the current situation of gas drainage and sealing in this coal seam, combined with the existing grouting and sealing technology, it is proposed to use pressure grouting and sealing to realize the sealing of deep coal bodies in the hole wall. According to the field conditions, the experimental pressure sealing parameter index is as follows: theoretical sealing length L1 = 9.69 m, the sealing length L2 = 13.98 m is verified, and the final sealing length is determined to be 15 m; the sealing radius is determined to be 0.6 m; the cement slurry was prepared on site with a water: cement ratio of 2:1; PG = 0.43 MPa was calculated; the range of the slurry diffusion radius R was 93.4–176.6 cm; the grouting pressure was determined to be 0.516 MPa. Field application practice has proved that: (1) Under the same drilling parameters and sealing parameters, the gas drainage effect of drilling with pressure sealing is 2.3 times higher than that without pressure sealing; (2) Using traditional sealing technology for drilling holes, the gas extraction concentration is far lower than the sealing operation effect of using the pressure sealing process; (3) Reasonably extending the length of the gas extraction drilling and sealing is a basic guarantee for realizing a substantial increase in the gas extraction concentration; (4) Sealing with pressure leads to a reliable and stable hole process.

Research on the Performance of Cement-Based Composite Borehole Sealing Material Based on Orthogonal Test

“…And on this basis, methods such as hydraulic fracturing coalbed water injection were improved so as to improve the extraction efficiency of coalbed methane. ,,− The first method has been widely used, with the increasing depth of coal mining, the underground environment is more and more complex, the performance of the commonly used sealing materials can not meet the needs of the project site. Especially for the “three soft” coal seams and other special coal seams, the long condensation time and the insufficient strength of the material are easy to cause problems such as collapse in the extraction process. − Finding a way to enhance the rapid solidification properties of the hole sealing material has emerged as a pressing issue. − Fly ash and poly­(vinyl alcohol) (PVA) fibers are commonly employed in cementitious materials. Fly ash is a byproduct of thermal power generation, and excessive accumulation of fly ash can have detrimental effects on the environment.…”

“… 16 − 18 Finding a way to enhance the rapid solidification properties of the hole sealing material has emerged as a pressing issue. 19 − 21 Fly ash and poly(vinyl alcohol) (PVA) fibers are commonly employed in cementitious materials. Fly ash is a byproduct of thermal power generation, and excessive accumulation of fly ash can have detrimental effects on the environment.…”

Study of Reasonable Grouting Pressure in the Process of Measuring Coal Seam Gas Pressure and Application

“…In order to determine the reasonable grouting pressure under specific surrounding rock conditions, this paper analyzes the influence of surrounding rock structure characteristics on the grouting effect by combining the rock lithology at the pressure measuring site of Pingdingshan No. 13 Coal Mine and the rock mass physical and mechanical properties. Considering the different lithology around the boreholes, the slurry diffusion radius under distinct grouting pressures is studied by numerical simulation, and a reasonable grouting pressure is selected, which can provide experience in grouting and hole sealing for mines with similar geological and gas occurrence conditions.…”

“…According to different sealing materials, common sealing methods include mud sealing, cement mortar sealing, rubber ring sealing, polyurethane foam sealing, etc. Considering the quality, cost, and difficulty of the sealing process, grouting sealing is the most widely used method up to now . However, its disadvantage is that when the hole sealing segment is in the soft rock or there are microcracks around the drilling hole, or when the pressure measurement drilling hole is constructed directly in the coal seam, good sealing quality cannot be guaranteed, and the sealing section is prone to gas leakage, resulting in the outcome lower than the actual one.…”

Discrimination Method of Gas Pressure Measurement in Coal Seams: Physical Experiment and Model Development

“…In the process of gas pressure measurement, the construction technology and gas occurrence conditions in the coal seam have an impact on its accuracy. Among them, construction technology involves sealing methods and sealing materials, and sealing methods are mainly divided into solid sealing and liquid sealing. The solid sealing method mainly includes the yellow mud sealing method, grouting sealing method, polyurethane sealing method, and apron capsule sealing device pressure measuring method. − The poor fluidity of solid materials may cause incomplete sealing of cracks, resulting in seal failure and inaccurate pressure measurement.…”