CENTENNIAL COAL Handling Gas Problems at Tahmoor Colliery Bob Newman, Ventilation Officer
Tahmoor Colliery Located approx. 70km SW of Sydney Underground Coal Mine Depth of cover 380 500 m Commissioned in 1979 Longwall introduced in 1986 Rail transport to Port Kembla Coal Loader Reserves for more than 25 years production within 3 leases
General Geology
Geological Sections -90-100 -110-98.0 BASE OF STANWELL PARK CLAYSTONE TNC 24 STANWELL PARK CLAYSTONE TMC 3-120 -114.0 STANWELL PARK CLAYSTONE -122.2-130 BASE OF SCARBOROUGH SANDSTONE BASE OF WOMBARRA SHALE BASE OF SCARBOROUGH SANDSTONE -140-138.5-143.8 BALGOWNIE SEAM -145.5 BASE OF WOMBARRA SHALE -150-153.5 CAPE HORN SEAM -153.0 BALGOWNIE SEAM -160-170 -180-169.0 TOP OF UPPER WONGAWILLI SEAM BASE OF LOWER WONGAWILLI SEAM -178.0 CAPE HORN SEAM TOP OF UPPER WONGAWILLI SEAM BASE OF UPPER WONGAWILLI SEAM TOP OF LOWER WONGAWILLI SEAM BASE OF LOWER WONGAWILLI SEAM BALGOWNIE SEAM CAPE HORN SEAM BULLI SEAM -167.6-174.1-181.3-190 BASE OF UPPER WONGAWILLI SEAM BASE OF LOWER WONGAWILLI SEAM -194.2-200
34 32 31 33 29 28 A 24 30 28 27 B 26 25 24 23 B 23 A A B 1500M 1000 500 0 Tahmoor Colliery Workings
Tahmoor Colliery Early days Mine development commenced 1978 Designed as Continuous miner operation Extraction using Wongawilli system 5 units set-up 4 prod, 1 spare No 1 shaft return, No 2 & drift intake
Tahmoor Colliery Upgrade Longwall introduced 1986/87 No 3 shaft sunk as new return Gas drainage introduced to pre drain L/W blocks & post drain L/W goaf Surface vacuum plant 1x 4000 m3/hr & 1x 2000 m3/hr Siemens pumps (provision to increase to 4x 4000 m3/hr). Designed to operate at 40-50 kpa. Plan for dual system never used 2x Schmidt-Kranz drill rigs (modified) for in-seam holes all rotary drilling
Early methods of dealing with outburst problem Outburst problem recognized quite early in mine life progressed from slumps, pressure bumps. All big outbursts on structures dykes or faults Mining under bomb squad conditions c/m driver had O 2 bottle & mesh screen; all other personnel retreated o/bye c/t Inadequate fatality in 200 area
Improved methods of dealing with outburst problem Outburst miner developed fully enclosed cab; 2 air supply systems; remote operation of s/c flights; breathing suits for bolting. Worked well but very slow. Remote mining with full face miner (ABM 20 s) remote cabin with radio control & CCTV worked well but also very slow Grunching (remote mining) current system when necessary; effective & practical; still slow but faster than previous methods; introduces other risks associated with explosives; problems with supply of P5 powder
Outburst prevention Work by many people (Alan Hargraves, Ripu Lama, Ray Williams, John Hanes, et al) led to development of pre-drainage to remove outburst risk Development of directional drilling a great benefit Current state is that drilling for prevention of outbursts is the main driver and degassing coal for L/W prod is a by-product (for in-seam drilling at least)
DRILLING PLAN PLAN SHOWING PROPOSED INSEAM DRILLING AS AT AUGUST '05
Tahmoor drilling equipment 1 x Longyear LM55 (drill to 400m) 2 x Kempe (1 drill to 800m 1 to 1100m) 1 x Ramtrack (for cross-measure drilling) 2 x Propets ( for coring & scout holes) 1 x VLD rig for longer holes & exploration 1.5 x acoustic tools 3 x Mecca (2 in storage in next l/w block) 1 x DGS (+1 on order)
Drill patterns In seam: Mostly cross-hole where possible; where not possible try & drill long holes parallel to hdgs, avoiding line of hdg Usually drill on fan pattern from 10m stubs off gate roads Try & limit branches to 1 (ie 2 holes per standpipe) Work on approx 15m spacing as standard 96mm holes from 100mm standpipes (copper)
Drill patterns (contd) Cross measure: Work on approx 20m spacing, avoiding c/t s Drill at 90 degrees to hdg on approx 17 degrees dip 65mm holes with 50mm standpipes (steel)
Plumbing All holes fitted with measuring sets In seam holes connected to gas mains via 100mm suction hoses, usually connected to a 150mm manifold valve at standpipe & at manifold Cross measure holes usually direct onto mains via 50mm suction hoses Gas mains are 350mm in panels & 450mm in main roads oversize to allow for water/silt. Ideally valves at every branch & approx every 800m or so Water traps (manual) at potential collection points
Hole monitoring Purpose to check hole is working (blocked or hard to drain area), estimate drainage effectiveness & identify air leakage sources Contractor on approx 3 days/week Readings on each hole weekly initially then decreasing frequency (also affected by access) Bag samples as often as practical
Flow Rate (l/min/m) 803 6 C/T Flow Rate per Hole 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 803D01 803D02 803D03 803D04 803D05 803D06 803D07 803D08 803D09 0 20 40 60 80 100 120 140 160 180 Days
Flow Rate (l/min/m) 803 10 C/T Flow Rate per Hole 6.0 5.0 4.0 3.0 2.0 1.0 0.0 802D31 802D32 802D33 802D34 802D35 802D36 802D37 802DD 0 50 100 150 200 250 300 350 Days
Outburst TLV s Originally the standard of approx 6.5 m3/t for 100% CO2 to 9.5% m3/t for 100%CH4 All life threatening outbursts at Tahmoor have occurred on structures which would be readily identified by drilling (dykes & large faults) Based on the above & Ripu Lama s work now have 3 TLV s allowing normal mining or mining at reduced rates (structured & non structured)
Qm=Q1+Q2+Q3 (m 3 /t) Tahmoor TLV s Thresholds for Outburst Procedures Unrestricted Mining Mining Structured Coal Mining Unstructured Coal 14 12 No mining 14 12 10 10 8 8 6 4 5.60 6 4 2 2 0 0 0 10 20 30 40 50 60 70 80 90 100 % CH 4 (rest is CO 2 )
Borehole maintenance Not a lot Monitoring contractor will identify obvious problems at hole collar/ plumbing area Monitoring results may indicate a possible blockage Sealing or hosing over after intersection a major leakage problem
Hard to drain areas Only apparent from 513 panel, possibly because of longer drainage times before then Occur in zones, but not consistently within those zones No readily apparent difference in coal in hard to drain areas (often, but not always, harder & stronger) Plainly areas of low permeability, but not sure of cause Work done on relating filling of micro fractures by foreign material to these areas (ongoing)
Overcoming hard to drain problem Have not yet succeeded When/if cause identified need to extend this to locating these zones & then to fixing them Hole slotting using high pressure water cutting some indications of success Hydrofraccing some indications of success Systems not easy to include in normal operations (time, resources, space, power supply, etc)
Post drainage Effectiveness not really known, but not game to find out Tried various patterns but parallel holes works best Not all holes produce large flows & no pattern evident Need gas from these holes to dilute air in the gas ranges or greatly improve hole sealing
Flow Rate (l/min/m) 801 post drain holes 30-44 45.0 40.0 35.0 30.0 25.0 20.0 15.0 10.0 5.0 Flow Rate per Hole XM30 XM31 XM32 XM33 XM34 XM35 XM36 XM37 XM38 XM39 XM40 XM41 XM42 XM43 XM44 0.0 0 20 40 60 80 100 120 Days
Flow Rate (l/min/m) 802 post drain holes 30-44 45.0 40.0 35.0 30.0 25.0 20.0 15.0 10.0 Flow Rate per Hole XM30 XM31 XM32 XM33 XM34 XM35 XM36 XM37 XM38 XM39 XM40 XM41 XM42 XM43 XM44 5.0 0.0 0 20 40 60 80 100 120 Days
Airway gas problem Problem maintaining statutory limits on l/wall face & in returns working with exemptions at present, 2% on face & 3% in returns Largely a vent problem & plans in place for new fans with much higher pressures (+4.5kPa vs 2.7kPa) Problem worse on L/W 22 even though vent much the same as previous walls
Airway gas problem (contd) Source of bulk of gas not clear do not believe it comes from roof, but source must be close to seam Balgownie seam suspected. Bulli seam remaining gas content low Tried holes drilled into Balgownie seam which produced reasonable flows but no clear benefit on face
Flow Rate (l/min/m) Holes in Balgownie seam Flow Rate per Hole 12.0 10.0 8.0 6.0 800B6D01 800B6D02 800B6D03 800B6D04 800B6D06 4.0 2.0 0.0 0 10 20 30 40 50 60 70 80 Days
Plans to overcome airway gas problem New fans with upgrade of vent control devices necessary Possibly continue trials of holes in Balgownie seam but not as easy as for L/W 22 Possibly improve goaf seals behind wall & apply suction to back of goaf
What developments would we like to see? Any improvements in drilling always welcome faster, cheaper or whatever Quick, cheap & effective method of sealing intersected holes Good automatic system for draining dirty water from gas lines Method to readily identify hard to drain coal Method to improve permeability Method to identify outburst prone areas other than gas content