THE BOREHOLE MONITORING EXPERIMENT

1. THE BOREHOLE MONITORING EXPERIMENT SJ Schatzel, CO Karacan, GV Goodman, R Mainiero, F Garcia1 NIOSH PITTSBURGH RESEARCH LABORATORY Disaster Prevention and Control Branch 1Retired

2. NEW INFORMATION CIRCULAR • Summary of five years of research on longwalls • Highlights of eight NIOSH publications • Formatted as guidelines for the industry

3. BOREHOLE MONITORINGEXPERIMENT (BME) • NIOSH sought to reduce the potential for explosions through enhanced methane control methods • Better understand the reservoir characteristics that influence gas emissions • Increase predictive capabilities, identify when and where methane migrates, gas responses to the mining process

4. BME-COOPERATIVE RESEARCH EFFORT • Research goals for cooperator • Document changing borehole permeability relative to longwall face location • Configure optimized borehole placement

5. THE BOREHOLE MONITORING EXPERIMENT (BME)

6. BOREHOLES FOR THE BME Drill sites Borehole collar

7. BOREHOLES FOR THE BME Borehole logging

10. EXPERIMENTAL INSTRUMENTATION • Downhole submersible pressure transducers • Surface pressure transducers • Surface methanometers • Borehole-mounted tiltmeters • Conventional positional surveying • NIOSH monitoring array GGV gas production

11. BOREHOLE PERMEABILITY • Three intervals determinations: pre-mining, during undermining, and post-mining • Slug testing results: • Pre-mining permeabilities for BH-1, BH-2 and BH-3 were 2.8 md (millidarcies), 0.1 md, and 0.2 md • After the pre-mining test, instrumentation failure in BH-3

12. BH-1 UNDERMINING 400 md, 100 ft ahead of mine face

13. BH-2

14. FINAL SET OF BME PERMEABILITY TESTS • Final slug tests were performed after mining had neared panel completion • BH-1 measured 63 and 65 darcies, 40 to 60 times the during undermining values • In BH-2, water head build-up could not be achieved, the permeability was much higher than in BH-1

18. SURFACE TILT BH-1 Tilt perpendicular to face Tilt parallel to face Surveyed position BH-2 BH-3

19. PERMEABILITY ANALYSIS • Combined reservoir and rock mechanics analysis estimate Pittsburgh Coalbed permeability distributions • Estimates lacked independent calibration data, were limited to the mining horizon • Subsidence data used as a proxy for induced fracture permeability distributions

20. - 0.0 - 0.2 - 0.4 - 0.6 - 0.8 - 1.0 - 1.2 1.4 m -120 -100 -80 -60 -40 -20 0 20 40 60 80 100 120 140 m

21. SURFACE CURVATURE • Tensional and compressional zones used to describe zones of high fracture permeability • Surface curvature profiles placed the inflection point transition 61 m (200 ft) from the gateroad • Data suggests 76 to 91 m (250 to 300 ft) from the tailgate will produce effective GGV performance

22. SUMMARY AND CONCLUSIONS • In situ borehole permeabilities prior to undermining were 2.8 md (millidarcies), 0.1 md, and 0.2 md • The fracture network formed 24-46 m (80-150 ft) ahead of the longwall face, Northern Appalachian Basin supercritical panel • Permeabilities during undermining BH-1 and BH-2 increased 100 to 500 times, higher instantaneous peaks

23. SUMMARY AND CONCLUSIONS(continued) • After being mined undermined BH-1 (Sewickley Coalbed) had a permeability of 63 to 65 Darcys, 40 to 60 times the during undermining values. • Borehole 2 (limestone and shale interval) had a higher permeability.

24. SUMMARY AND CONCLUSIONS (continued) • Vertical surface movement ended 58 to 88 m (190 to 290 ft) behind the longwall face • Surface tilting continued 160 to 190 m (520 to 620 ft) behind the longwall face • The onset of maximum fracture permeability may correspond to a position 58 to 190 m (190 to 620 ft) behind the face

25. ACKNOWLEDGEMENTS • Staff and management from an anonymous mine operator • C Hollerich, JP Ulery, J Marshall, MA Trevits NIOSH PITTSBURGH RESEARCH LABORATORY Disaster Prevention and Control Branch