ICGCM Papers:
Longwall Mining
 
 
Mitigation of a Massive Sandstone Channel’s Impact on Longwall Face Evaluation and Enhancement of Hydraulic Fracturing Technique
33rd International Conference on Ground Control in Mining
Mitigation of a Massive Sandstone Channel’s Impact on Longwall Face Evaluation and Enhancement of Hydraulic Fracturing Technique
by
Jun LuDaniel W.H. SuGreg J. HasenfusMark VAn DykeLuke Stull, Consol Energy Inc., Canonsburg, United States
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[Conference] 33rd International Conference on Ground Control in Mining
[Price] Free  [Comments] 0
[Topical Area] Longwall Mining
[Author] Jun LuDaniel W.H. SuGreg J. HasenfusMark VAn DykeLuke Stull, Consol Energy Inc., Canonsburg, United States
[Abstract] 
Key Conclusions:
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The panel #22 sandstone channel has been successfully mined through from late December, 2012 to early February, 2013. Results from daily underground observations and production delay analysis show that longwall face conditions and advance rate were significantly improved comparing to those of panel #21. Also, safety was improved for underground personnel, since large chunks of sandstone laying on the face conveyor creates tremendous safety hazards.
Key Findings:
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Each frac hole in panel #21 was fraced and pumped with an average water volume of 14,000 gallons and at an average pumping rate of 25 barrels per minute. Based on the analysis and evaluation in panel #21, more water could have been pumped into each frac hole to propagate the individual horizontal pancake fractures to enable them to overlap one another to enhance caving and to relieve face pressure. Therefore, approximately 1,000 barrels or 42,000 gallons of water were used for each frac hole in panel #22. Also, to ensure proper propagation of the horizontal pancake fracture, a pumping rate of 35 barrels per minute was maintained throughout the pumping process for each frac hole. As in panel #21, LVA software was also employed to guide the longwall face crew to institute shields double-pull behind the shearer drum to reduce the tip-to-face distance at the critical spots along the longwall face, which mitigated the formation of the roof cavity and sandstone falls. LVA recording and underground observation results show that there was a very strong correlation between the LVA cavity index and the observed sandstone falls at the face.
Objective of the Paper:
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Based on the experience in panel #21, more water was pumped into each frac hole in panel #22 to propagate the individual horizontal pancake fractures to enhance caving and to relieve face pressure. The Longwall Visual Analysis (LVA) software was also employed at panel #22 to predict the cavity risk index. The primary objective of this paper is to evaluate the effect of the extended horizontal pancake fractures on the face conditions, productivity, and safety in panel #22.
Problem Statement:
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A nearly 1,000 ft wide sandstone channel was projected to run through the mid panel area of three consecutive longwall panels (#20, #21 and #22) in a southwestern Pennsylvania coal mine. This sandstone channel was known to cause serious longwall face roof control problems in the mine’s B-panel area in 1998 and 1999. Most recently, it induced many large face cavities and caused substantial production delay in panel #20. Hydraulic fracturing technique and Longwall Visual Analysis (LVA) software were employed to mitigate its impact in panel #21. Comparing to panel #20, improved longwall face conditions and productivity were observed as panel #21 mined through the sandstone channel. However, a few moderate sandstone fracturing and falls at the face were still present in areas where horizontal pancake sandstone fractures were not present. Such adverse face conditions caused two to three weeks of production delay due to large face cavity, jammed panline and subsequent face gluing.