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Managing risks from underlying workings
This presentation provides an overview of Metropolitan Coal longwall operations after a gas inundation event on 21 March 2019 from the underlying coal measures. The event itself resulted in carbon dioxide and methane levels increasing unexpectedly to hazardous levels, leading to the safe evacuation of 70 workers and an idle period of seven days before access could be safely reestablished underground. The presentation provides a review of the gas inundation event, the system changes and technological solutions aimed at reducing personnel exposure. It examines the learnings from the event including an understanding of the gas reservoir surrounding the operating seam and some of the challenges/benefits post-implementation of remote longwall mining techniques.
Managing risks from underlying workings
- 1. Presenter: Jon Degotardi Longwallmining in floor break and outburst risk areas Managing risks from underlying seams 4 December 2019 Metropolitan Mine
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- 3. 3 $185M Metropolitan 2018/19 wagesand businesses in local and regional economy Community Peabody actively supports community groups, sporting clubs & events Metropolitan Mine $22M Royalties to NSW economy 2018/19 415 Local jobs, 95% of employees live locally in communities such as Helensburgh and Wollongong 1888 One of the oldest, longest continually running mines in Australia – 131 years
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- 5. Summary of LW303floor break Source: www.resourceregulator.nsw.gov.au
- 6. Tube Bundle MonitoringLW303 Return 6 Re-entry 3 hours
- 7. 10541 101,816 319,362 202,090 163,328 142,931 130,387 125,362 AVEDAY MAR 2019 DAY 1 (6HRS) DAY 2 DAY 3 DAY 4 DAY 5 DAY 6 DAY 7 CH4 m3/day 94867 184,813 451,776 337,884 288,256 260,937 243,634 237,989 AVE DAY MAR 2019 DAY 1 (6HRS) DAY 2 DAY 3 DAY 4 DAY 5 DAY 6 DAY 7 CO2 m3/day Ventilation 7 Peak levels measured in the Longwall Return Airway • 16.1 % Methane • 15.9 % Carbon Dioxide Scenario Levels Volume Co2 3.00% 228 m3/s CH4 1.25% 554 m3/s To dilute peak gas using ventilation 30x change Average Daily Release Average Daily Release 4x change
- 8. Longwall Face Mapping- Post Event 8 Longwall standing for 6 days No evidence of a geological structure in face Observed conditions were typical of normal mining Longwall 303 Goaf Direction of Retreat
- 9. Metrop longwall installation– Bulli Seam Understanding the gas source
- 10. Outburst and GoafFloor Emission History 10
- 11. Outburst and GoafFloor Emission History 11
- 12. Bulli Seam GasDrainage 12 In seam gas drainage 130km per year Gas content confirmed prior to authorizing mining Floor Break
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- 14. Longwall geometry andfracturing ● Longwall extraction create 163m void width ● Chain pillars left adjacent to void 45m wide (Solid) ● Fracturing occurs both above and beneath the void 14 Longwall 130 m 50 m CO2 CH4 Fracture Zone Fracture Zone 270 - 420 m
- 15. Interburd en 50% Coal Seams 50% - 200,000 400,000600,000 800,000 1,000,000 1,200,000 BULLI BALGOWNIE INTERBURDEN BALGOWNIE CH INTERBURDEN CAPE HORN HARGRAVE INTERBURDEN HARGRAVES W1 INTERBURDEN WORONORA 1 W2 INTERBURDEN WORONORA 2 WONGA IB 6 day gas volume (m3) contribution by formation Typical gas liberation expected in 6 day period 15 ~0.6 Million m3 90% CO2 / 10% CH4
- 16. - 200,000 400,000600,000 800,000 1,000,000 1,200,000 BULLI BALGOWNIE INTERBURDEN BALGOWNIE CH INTERBURDEN CAPE HORN HARGRAVE INTERBURDEN HARGRAVES W1 INTERBURDEN WORONORA 1 W2 INTERBURDEN WORONORA 2 WONGA IB 6 day gas volume (m3) contribution by formation Interburd en 83% Coal Seams 17% Post event analysis and sampling below seam 16 30% ~2.9 Million m3 62% Co2 / 38% CH4
- 17. Source of gas– vertical distribution 17 CO2 Laminated Carbonaceous Shale with Sandstone CH4 CO2 >80% >90% 50-60m CH4
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- 19. Identified key areasfor improvement 19 ● Management plans – Reviewed for possibility of floor break without presence of structure – Exclusion of personnel from the returns during production shifts ● Hazard prediction plans changed to reflect new knowledge – Key communication tool updated with colour coded assessment of floor break risk ● Gas drainage drilling targeting gas reservoirs beneath the operating seam Recognition that inter burden contained significant quantities of gas ● Continued progress towards automation of longwall – Technological change accelerated to put distance between people and potential hazards – Remote mining to removes personnel from the face
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- 21. Drilling Cross measure drainage– “down holes” 21 Cross Section Plan View 50m
- 22. 22 Previously – peopleon face during shear cycle
- 23. Challenges experienced duringLW27 and 301 remote mining 1. Consistently maintaining cut horizon whilst operating remotely 2. “User Friendliness” of previous “Mimic Steer/ Fixed Extraction Method” 3. No visibility of Longwall Face (only telemetry) 4. Excessive damage to ranging arms due to collisions 5. Poor production rates (70 to 90 minute shear cycles) Review of previous remote operations at Metropolitan with a view of enhancing our capabilities 23
- 24. Enhancements made duringLW303-304 changeout and commissioning of LW304 1. Design and Implementation of Longwall Camera Network 2. Longwall Camera Position and lighting trials 3. Upgrade Longwall PC’s 4. Purchase and implementation of Komatsu Mining Corp. (KMC) Pitch Steer Software 5. Configuration and implementation of remote health monitoring 6. Commissioning of CME mounted “Teleremote” hardware 7. Retrofit of CME Mounted “Master Control Mimic” 8. Crew training for Pitch Steer Preparation for LW304 Remote Mining 24
- 25. Longwall Camera Positions– 6 installed, another 6 planned 25
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- 27. 1. Implementation ofCamera Network and Pitch Steer software 2. Operator Training across all shifts 3. Initial Operator push back to Cameras 4. Drill Rod Management 5. Cutting out TG and not cutting brattice or roof mesh 6. Several instances where operators trammed Shearer without cutters running / or broken shear shaft which lead to spill tray damage. (PLC Code created to detect broken Shear shaft / cutters not running and halt tramming function) Challenges 27
- 28. Advantages – improvingcut time 28 Event Remote Operations Improving cut time
- 29. Advantages – improvingyield or cut quality 29 Remote Operations Event Pitch Steer Commenced Cameras
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Editor's Notes
- #3 Underground coal mine Located in Helensburgh - 40km south of Sydney, 30 kilometers north of Wollongong Metallurgical Coal for Steel, 50% domestic customer (Bluescope), remainder exported to Europe and India Longwall extraction is mining method
- #4 Commenced operations in 1888 and have been in production ever since –131 years old This year we provided $185M in wages and business purchases in the local economy, plus $22M in royalties to NSW Approximately 415 Employees and contractors employed onsite, proactive in community supporting more than a dozen community organisations Helensburgh Tigers – football club Helensburgh-Stanwell Park Surf Life saving club Holy Cross Primary School – environmental & permaculture programs Helensburgh Primary School – environmental & permaculture programs University of Wollongong - STEM camp for girls Helensburgh Cricket Helensburgh Junior Soccer - Thistles Helensburgh Tennis Club BMX Sponsorship – Kai & Saya junior BMX champions Helensburgh Mens Shed - Hopehealth Illawarra Convoy – Kids cancer charity Rotary Club – local functions Lions Club – local functions Helensburgh Fair Other Festivals Santa firetruck lollies Christmas Fireworks Helensburgh Christmas Carols
- #5 Aa bit of background on Metrop and the mine layout. Longwall extraction began in 1995 (Longwall 1) and is ongoing to present (Longwall 304). This is our 30th longwall to be extracted at Metrop, the 9th with current LW (Joy/Komatsu equipment) We mine the Bulli Seam at a nominal thickness 3m And produce approximately 1.8-2.0 million tones per annum. Owned and operated by Peabody
- #6 Driver or motivator behind todays presentation on longwall mining
- #7 Snapshot of the event - from the TG tube bundle monitoring point Re-entry after 6 days Quantity of gas = ~3 Million m3 of gas released in these 6 days TARP’s and withdrawal procedures followed in this time frame Peak levels measured in the Longwall Return Airway. 16.1 % Methane 15.9 % Carbon Dioxide
- #8 Looking at gas emissions that occurred – 4 fold increase in CO2 and 30 fold increase in Methane To answer a ventilation question up front… Just how much ventilation would be needed to dilute this event to statutory levels…550m3/s…. Almost twice the main fans capacity on the face 280m3/s Additional information: Main vent system consists of 2 x Flaktwoods fans in parallel with a total quantity of 280m3Sec at a collar pressure of 3.4Kpa. LW intake 61m3Sec LW face 48m3Sec LW return 43m3Sec LW Bleeder 18m3Sec with 5 m3Sec bleeding through the goaf.
- #9 Longwall standing for 6 days Post incident: MG, TG and Face conditions typical of normal mining No evidence of geological structure in the face (Bulli Seam)
- #10 Next few slides are background on gas at Metropolitan Previous events Composition Typical gas drainage pattern Roof fracturing effects of floor fracturing external to the coal seam
- #11 For those in audience not familiar an Outburst is sudden and often violent release of gas and coal from the coal seam due to differential gas pressure Goaf Floor fracture can result in an Inundation of gas through the fractures that act as a conduit from a reservoir above or below the seam At Metropolitan the first recorded outburst in NSW occurred in 1895 and claimed the lives of 3 miners and a horse. Since 1895 Metropolitan has recorded over 150 of which approx. 100 historical events are not shown on this plan they were induced by shot firing undrained coal. Shown on this plan you can see the trend of events clustered in certain areas, the reason has traditionally been related to geological structure…
- #12 Hargraves & Lunarzewski (1985) showed that gas composition in proximity to Metropolitan Fault is predominantly CO2 on upthrown side and CH4 on downthrow side. During the setup for LW303 there was no apparent faulting mapped in the planned extraction panel (LW303) and No anomalies ere detected during Bulli Seam pre-drainage Geological feature nearby are 2 significant strike-slip faults in adjacent LW304 F-0008 strike slip fault zone 3 x outbursts 3x Floor breaks 4km strike length F-0027 strike slip fault zone was first intersected during the development of MG304. There was no evidence of F-0027 during MG303 development or in the subsequent geological mapping for LW303. This fault has now been intersected in MG305 and associated with 1 potential outburst event
- #13 Bulli Seam gas drainage coverage at LW303 incident location and typical of pre-mining preparation, for outburst risk management 130-140km of gas drainage drilled per year to remove gas from the worked seam. Typically design to have hole toe spacing at 12.5m in adjacent development roadways and 30m in longwall block. Every shear that the longwall takes requires ~40m of drilling
- #14 Video graphic to help understand longwall effects creating fractures above the operation. Depth of cover is 400 to 550m with Fracturing above the extracted area extending 130m
- #15 Not only is their fracturing above the seam but the floor below the void softens and fractures, modelling for Metrop indicates this is in the vicinity of 50m Solubility characteristics of CH4 & CO2 in water result in vertical gas composition changes. CH4 comes out of solution first (at greater depth or pressure), followed by CO2 comes out of solution at shallow vertical water pressure. Other Metropolitan Longwall 89 face supports, each with capacity = 1,170 tonnes
- #16 Based on expected gas sources and typical flows from prior 2 longwalls this was the expected typical 6 day profile of source emissions 0.6Million m3 at 90%/10% Decreasing gas contributions with depth and sufficient to match the observed gas profile Bulli seam contribution from cutting and loading out coal during normal operations
- #17 What was observed after the event and post additional sampling below the seam. ~3 Million m3 of gas released in 6 days at 62%/38% In order to match the mix of gasses and the known gas contents (fingerprinting the source) the interburden contribution makes up the majority of gas, in particular interburden above Woronora Seam Woronora Interburden – banded or laminated carbonaceous shale/sandstone…. overslide Background Interburden increased from 1.0m3/t to 2.63m3/t (Woronora Interburden)
- #18 Woronora Interburden – banded or laminated carbonaceous shale/sandstone Laminites – above the Woronora Seam – essentially carbonaceous shales intermixed with sandstones 2.6m3/t Recognising that with the majority of gas emanated from interburden or rock (RD 1.7) then the possibility of gas drainage effectiveness would be limited, rather additional other controls would be required.
- #20 Administrative / engineering / isolation
- #21 Gas Inundation risk ranked using a colour code system The drivers used for changing gas inundation risk include: Goaf square up, development of full abutment loads and enhanced depth of softening to the lower coal measures; Proximity to previous goaf; The occurrence and likely nature of faulting; Proximity to historic events (LW303); and Depth of cover. Controls Green (Low) risk ranking: Remote mining not required. Time used to train operators in remote mining procedures including pitch steer Orange (Low to Moderate): Remote mining in place and cross measure drainage holes Pink (Moderate to High): Remote mining in place, cross measure drainage holes and increased awareness for signs and symptoms, mine personnel refresher on zone.
- #22 Designed to maximize the number of intersections with LW mining induced floor fractures Designed to reach 50m depth and the Woronora Seam Fracture characterization based on Strata Control Technologies numerical modelling work Aimed at limited pre drainage gas capture but mainly activation on longwall abutment front fracturing to capture more gas into the pipe range rather than the return airways.
- #24 note LW301 had operators positioned approx. 170m Outbye of MG Corner
- #25 CME – Control and Monitoring Enclosure
- #26 Rugi Mk2 cameras. Orientated with ventilation, positioning of lights, cleaning schedule Current Camera Locations Midface / General (Bretby Crossover) TG Cutout X 2 ( Brattice and Mesh) Drill rods Face ( Monitoring drill rods) General area X 2 ( Monitoring PRS collisions etc..) 6 more to be retro fitted to provide better continuity of vision across entire cycle. All available externally with web page of live camera feeds. Possible live link during conference? VPN into system
- #28 Drill rod management - During start up of remote operations also had to deal with 300m of drill string bogged in longwall block
- #29 Key Takeaway - change can be good Production budget cut time is 50mins per shear improving cut times (repeatability) Host of other benefits, Health or dust exposure, operator exposure to face spall, exposure to hydraulics Stepping safely into the future Quality of mining – dilution, speed, repetitively all improving with use of technology
- #30 Initially remaining LW303 remote operations controlled by operator recording up down movements