Study on Effective Extraction Radius of Directional Long Borehole and Analysis of the Influence Mechanism

Abstract

To accurately determine the effective extraction radius of directional long drilling, the influence of the negative pressure of the hole mouth, the drilling diameter, and the drilling length of the hole on the effective extraction radius of a directional long drilling hole is simulated by establishing a coal-to-gas gas-structure coupling model considering the Klinkenberg effect. Finally, the reliability of the numerical simulation is verified through field testing in Yuxi Coal Mine. The results reveal that the attenuation of negative pressure in a directional long borehole along a long hole has a significant influence on the gas extraction effect. The radial gas pressure of the extraction drilling hole is distributed in a “V” shape when the negative pressure of the extraction decays along the direction of the hole length. The higher the negative pressure and the longer the diameter of the drilling hole, the higher is the gas extraction effect. The effective extraction radius is exponentially related to the drilled hole depth when the negative pressure of extraction is attenuated along the long hole direction. The negative pressure of the hole and the diameter of the borehole are linearly related to the effective extraction radius at the depth of drilling hole of 430 m. Through field tests, while extracting for 180 days based on the stubble pressing effect, the effective extraction radius of the directional long borehole of the No. 3 coal seam of Yuxi Coal Mine is 5.7 m, and the absolute error between the numerical simulation is 0.1 m. In addition, the gas pressure obtained from different sampling points is consistent with the numerical simulation. The relative error is 0.3–4.1%. The results provide a theoretical basis for the rational layout of directional drilling.

Fluid–Solid Coupling Characteristics of Methane-Containing Coal during Borehole Extraction of Coalbed: Numerical Modeling and Experimental Research

“…Zhang elucidates the test results of CBM extraction experiments under various borehole deformation instability conditions. It proposes a method for calculating the along-hole resistance coefficient of borehole walls, as follows λ false′ m = 64 ( 1 + 0.04304 italicRe 0.6142 ) , ( Re ≤ 2320 ) λ false′ m = false[ 1.14 − 2 lg ( ε / d + 21.25 italicRe − 0.9 ) false] − 2 × ( 1 + 0.0163 italicRe 0.2278 ) , ( Re ≥ 4000 ) It is necessary to calculate the Reynolds number of the CBM flow in the m-th infinitesimal segment according to the formula below to clarify the flow regime of this segment and determine its along-borehole resistance coefficient Re m = 2 ρ m ( 2 Q m − 1 + q m ) μ π d where ρ m is the average density of CBM in the m -th segment, kg/m 3 ; Q m is the original CBM content within the m -th borehole segment, m 3 ; q m is the amount of CBM influx into the borehole wall within the m -th segment, m 3 .…”

“…It proposes a method for calculating the along-hole resistance coefficient of borehole walls, as follows It is necessary to calculate the Reynolds number of the CBM flow in the m-th infinitesimal segment according to the formula below to clarify the flow regime of this segment and determine its along-borehole resistance coefficient. 43 where ρ m is the average density of CBM in the m -th segment, kg/m 3 ; Q m is the original CBM content within the m -th borehole segment, m 3 ; q m is the amount of CBM influx into the borehole wall within the m -th segment, m 3 .…”

Analysis of Influence of Geotechnical Dynamics Characteristics on Tunnel Engineering Design

“…Although the contact characteristics between surrounding rock and concrete lining are very important, they are rarely considered in most finite element numerical simulation, and few people have studied the change of contact characteristics over time. In the past finite element analysis, the influence of excavation footage and length of excavation step is rarely considered, while the time effect is rarely considered [8] . Therefore, it is necessary to further calculate and discuss the problem of tunnel excavation.…”

Study on Instability Characteristics of the Directional Borehole on the Coal-Seam Roof: A Case Study of the Tingnan Coal Mine

“…With the increase of borehole depth, the friction resistance gradually develops into an exponential relationship. In addition, Liu et al [28] concluded that the effective drainage radius of a directional long drilling hole has an exponential relationship with the distance from the drilling opening. Yuan et al [29,30] conducted the combined drilling method of curtain grouting in underground deep wells, which can significantly reduce the risk of water inrush in deep mining with complex hydrogeological conditions.…”