Determination of Gas Extraction Borehole Parameters in Fractured Zone on ‘Borehole in Place of Roadway’ Based on RSM-GRA-GA

Abstract

Large-diameter gas extraction borehole is considered an effective method by which to realize coal mine methane exploitation and outburst prevention. Efficient gas extraction can be achieved by selecting the right borehole parameters. In this paper, by comparing several conventional objective weighting methods, the PCA was used to assign the weights to the research indices, the optimization objective was reduced from multi-dimensional to one-dimensional with the help of the gray correlation analysis. The study of gas extraction effect under different borehole parameters based on the response surface model. Numerical simulations were used to analyze the mixed volume of gas extraction, the pure volume of extraction and the concentration in the upper corner after extraction under different schemes. Finally, a genetic algorithm degree model was used to solve the solution and determine the optimal arrangement of borehole parameters. The study shows that (1) the weight shares of borehole stratum, borehole diameter and borehole spacing were 0.385, 0.285 and 0.33, respectively, in the reduced dimensional analysis of the PCA. (2) Using the results of improved gray correlation analysis as a comprehensive evaluation value to measure the effect of gas extraction, the optimal range of the model was 28–30 m borehole level, 190–210 mm borehole diameter and 5.5–6.5 m borehole spacing. (3) Using the genetic algorithm to solve the model, we obtained the borehole layer 28.79 m, borehole diameter 199.89 mm, borehole spacing 5.76 m. The borehole gas extraction effect was good under this parameter. The extraction mixed volume was 129.8 m3/min, the extraction pure volume was 9.16 m3/min, the upper corner concentration was 0.52%, and the prediction accuracy of the model was 97.8%.

Substantiation of Drilling Parameters for Undermined Drainage Boreholes for Increasing Methane Production from Unconventional Coal-Gas Collectors

“…One of the most debatable areas is the prediction of zones with different parameters of the filtration channels "methane drainage zone" [23][24][25], which provide a decaying metastable solid gas-coal solution and the boundaries (angles of complete displacement) [26][27][28][29] for real conditions of reserve development. For this purpose, a commercial software, which implements numerical simulation methods, such as the finite element method (FEM) in COSFLOW [30,31], CFD gas flow in ANSYS [32,33], CMG-GEM [34], PFC2D [35], finite differential method (FDM) in FLAC3D [36], discrete models [37] (such as UDEC [38,39]), and physical simulation with equivalent materials [40], is widely used. At the same time, valid estimation methodologies are still lacking to fully understand the processes under study.…”

Study and Application of High-Level Directional Extraction Borehole Based on Mining Fracture Evolution Law of Overburden Strata

“…To obtain a good gas drainage effect, many scholars and experts have studied the designed position of boreholes based on the mining fracture evolution law of overburden strata [20][21][22]. Coal enterprises have carried out field tests on work planes using highlevel directional long borehole technology, which verified the effectiveness of this technology in gas extraction [23][24][25].…”