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Instability-negative pressure loss model of gas drainage borehole and prevention technique: A case study.

ABSTRACT: The internal collapse of deep seam drainage borehole and negative pressure loss represents a serious technical problem affecting gas drainage. To address this problem a creep model of coal around borehole was established based on the plastic softening characteristics of coal. The final collapse time of the borehole was determined and used to derive the three stages of the borehole collapse process. The model of negative pressure loss in drainage borehole was established according to the theory of fluid dynamics, the model of methane gas flow and the creep model of the coal around the borehole. The relationship between the negative pressure loss of drainage and the change of borehole aperture was derived, thereby revealing the main influencing factors of the negative pressure loss in the borehole. A drainage technique named "Full-hole deep screen mesh pipe" was introduced and tested to prevent the collapse of borehole and reduce the negative pressure loss. The result shows that after the borehole was drilled, the borehole wall was affected by the complex stress of the deep coal seam, the coal surrounding the borehole collapsed or presented the characteristics of creep extrusion towards the borehole. The "Full-hole deep screen mesh pipe drainage technology" could effectively control the collapse as well as the deformation of the borehole and reduced the negative pressure loss. Compared with the traditional drainage technology, the methane gas drainage concentration was increased by 101% and the gas flow was increased by 97% when the methane gas was drained for 90 days, the gas drainage efficiency increased significantly.

SUBMITTER: Qi Q

PROVIDER: S-EPMC7682895 | biostudies-literature | 2020

REPOSITORIES: biostudies-literature

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Instability-negative pressure loss model of gas drainage borehole and prevention technique: A case study.

Qi Qingjie Q Jia Xinlei X Zhou Xinhua X Zhao Youxin Y

PloS one 20201123 11

The internal collapse of deep seam drainage borehole and negative pressure loss represents a serious technical problem affecting gas drainage. To address this problem a creep model of coal around borehole was established based on the plastic softening characteristics of coal. The final collapse time of the borehole was determined and used to derive the three stages of the borehole collapse process. The model of negative pressure loss in drainage borehole was established according to the theory o ...[more]

PMID: 33227010

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Project description:To study the shrinkage rule of borehole diameter and its effect on gas extraction, a visco-elastoplastic model for boreholes considering strain softening and the dilatancy characteristic was established to obtain the expressions of the coal stress, variation in diameter, and pressure relief range. The stress distribution and pressure relief effect of the boreholes in soft and hard coal seams were comparatively analyzed. The shrinkage rule of the borehole diameter was studied. The reasons for the rapid reduction in the extraction concentration of the borehole in soft coal seams were described. A technology of improving the gas extraction effect in soft coal seams was developed. The research results showed that the radius of the plastic softening zone is 0.405 m for a borehole in a soft coal seam and 0.224 m for that in a hard coal seam. This indicates that the borehole in a soft coal seam has a better pressure relief effect. The boreholes in both hard and soft coal seams will incur a shrinkage phenomenon; however, the soft coal seam has low strength and a weak ability to resist damage, and thus the surrounding coal will have a more intense creep deformation, leading to an instability failure during a short period of time and thus, a blocking of the extraction channel, thereby causing a rapid reduction in the gas extraction concentration. The borehole in a hard coal seam also shows a shrinkage phenomenon, but remains in a stable state without a blockage; thus, high-concentration gas can be extracted from this borehole for a long period of time. The geo-stress and coal strength are the two main factors controlling the amplitude of borehole shrinkage. From an increase in stress, the borehole in a hard coal seam shows a more intense creep deformation in a deep mine, which may lead to blockage. The key to improving the gas extraction effect in soft coal seams is to maintain a smooth extraction channel. The full screen pipe is installed through the drill pipe to retain an extraction channel, leading to an average gas extraction increase from 0.043 m3/min to 0.12 m3/min, an increase of 2.77 times. These research results are consistent with actual production, and can provide theoretical guidance for determining the gas extraction parameters.

Project description:BackgroundBurr hole evacuation is a well-established treatment for symptomatic cases with chronic subdural hematoma (cSDH). Routinely postoperative catheter is left in the subdural space to drain the residual blood. Drainage obstruction is commonly seen, and it can be related to suboptimal treatment.MethodsTwo groups of patients submitted to cSDH surgery were evaluated in a retrospective non-randomized trial, one group that had conventional subdural drainage (CD group, n = 20) and another group that used an anti-thrombotic catheter (AT group, n = 14). We compared the obstruction rate, amount of drainage and complications. Statistical analyses were done using SPSS (v.28.0).ResultsFor AT and CD groups respectively (median ± IQR), the age was 68.23 ± 26.0 and 70.94 ± 21.5 (p > 0.05); preoperative hematoma width was 18.3 ± 11.0 mm and 20.7 ± 11.7 mm and midline shift was 13.0 ± 9.2 and 5.2 ± 8.0 mm (p = 0.49). Postoperative hematoma width was 12.7 ± 9.2 mm and 10.8 ± 9.0 mm (p < 0.001 intra-groups compared to preoperative) and MLS was 5.2 ± 8.0 mm and 1.5 ± 4.3 mm (p < 0.05 intra-groups). There were no complications related to the procedure including infection, bleed worsening and edema. No proximal obstruction was observed on the AT, but 8/20 (40%) presented proximal obstruction on the CD group (p = 0.006). Daily drainage rates and length of drainage were higher in AT compared to CD: 4.0 ± 1.25 days vs. 3.0 ± 1.0 days (p < 0.001) and 69.86 ± 106.54 vs. 35.00 ± 59.67 mL/day (p = 0.074). Symptomatic recurrence demanding surgery occurred in two patients of CD group (10%) and none in AT group (p = 0.230), after adjusting for MMA embolization, there was still no difference between groups (p = 0.121).ConclusionThe anti-thrombotic catheter for cSDH drainage presented significant less proximal obstruction than the conventional one and higher daily drainage rates. Both methods demonstrated to safe and effective for draining cSDH.

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Instability-negative pressure loss model of gas drainage borehole and prevention technique: A case study.

Publications

Instability-negative pressure loss model of gas drainage borehole and prevention technique: A case study.

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