1. Russell Thomas Gas Drainage Coordinator – Appin Colliery November 2014
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Update on Outburst Management at Appin Gas & Coal Outburst Committee - Wollongong
Russell Thomas
Gas Drainage Coordinator – Appin Colliery
November 2014 1

2. Update on Outburst Management
Outbursts during Dyke Extraction
Alterations to Appin Outburst Management Plan
This talk is intended to provide a brief update on a few issues related to Outburst Management recently. That is, a number of small outbursts that have occurred during the extraction of a dyke by shotfiring, and some minor alterations to the Outburst Management Plan at Appin that have been implemented to make the plan more focussed on the high risk areas.
Russell Thomas, Gas Drainage Coordinator - Appin Colliery, November 2014

3. Outbursts During Dyke Extraction
Typical Outburst Cone
Dykes are extracted by shotfiring ahead of longwall extraction
Multiple small outbursts have resulted:
Usually small amounts of material (~10t)
Usually small amounts of gas (<100m3)
>90% methane gas composition
Above 10m3t-1 total gas content.
No personnel exposed – all outbursts triggered remotely
Locations of outburst identified through tight regime of gas sampling
~ mm
Appin extracts a couple of dykes that run across the longwall blocks by shotfiring ahead of longwall extraction.
During the extraction of these dykes there have been a number (over 20) small outbursts that have all been triggered by shotfiring.
The outbursts are all reasonably small – generally less than 10t of material disloged and usually less than 100m3 of gas released. In this case, the gas is almost entirely methane. The gas content is generally above 10m3t-1, which is above Appin’s outburst threhsold.
The main reason for the outbursts occurring is the extremely complex geology of the dyke – the dyke where the outbursts have occurred has a number of related structures running parallel or sub-parallel to it – mainly a couple of slip/strike faults close to the dyke. These create small pockets of gas between the dyke and secondary structure.
The most important aspect to note is that no personnel have been exposed to these outbursts. They have been predicted and managed using a tiered threshold system, together with a very intensive tight pattern of coring and testing for gas content.
Russell Thomas, Gas Drainage Coordinator - Appin Colliery, November 2014

4. Management of Outburst Risk in Dyke
Multiple categories of risk management
“Zone A” – no restrictions
“Zone B” – corresponds to Gas Pressure of less than 500kPa, and accounts for small pockets of gas against the dyke – relieving shots required before slotting
“Zone C” – above Appin’s threshold – no slotting
“Zone D” – 3m3t-1 above Appin’s threhsold – no rotary/percussive in coal or cinder
Geological inspections at maximum intervals of a week to identify changes, particularly additional structures adjacent to dyke
Close spacing of gas content cores – approx 10m spacing along length of dyke
To manage the outburst risk during dyke extraction, the outburst threshold that apply to all mining at Appin have been extended beyond the “normal” or “remote” mining distinction that we apply to development with a continuous miner.
The threshold chart has been divided into four regions.
The best drained areas (below 5m3/t CH4 – 3m3/t CO2) are extracted without restriction from an outburst management perspective. (Zone A)
Once the gas content is above 5m3/t CH4 / 3m3/t CO2, but below the outburst threshold that Appin works to, we don’t allow a slot to be cut unless a number of relieving shots have been fired in the location of the slot. This serves two purposes – it accounts for any small pockets of gas that may exist adjacent to the dyke, and also opens any natural voids that do occur adjacent to the dyke and hold gas at around 600kPa (ie won’t “outburst” in the traditional sense, but will release gas under pressure if cut into). Once the area that the slot is intended for has been disturbed by a relieving round, a slot may be mechanically cut. This philosophy is consistent with the idea that men can work at the face up to the outburst threshold, but not above it. It also allows for the management of risks associated with a small pocket of gas – either held as free gas, or as a small pocket of seam gas that may have been missed between two cores.
Once the gas content is above the outburst threshold, there is no mechanical cutting performed at the face. This is consistent with the philosophy that cutting the face with men at the face is not allowed above threshold – whether it be on a continuous miner in a development panel, or in a dyke extaction panel. In this instance, we can either stop extraction, and drill/drain to reduce gas content, or ammend shotfiring patterns so that a slot is not used to create a free face adjacent to the dyke. Work has been carried out to determine whether it is safe to drill shotholes at the face above threshold, and it has been determined that it is acceptable to do so. A comprehensive review of experience drilling above threshold was conducted – some anecdotal evidence that could not be confirmed existed to indicate that some outbursts may have been triggered by drilling above 20-25m3/t, but significant experience in grunching on the South Coast indicated that it is acceptable to drill with men at the face.
Once more than 3m3/t above the outburst threshold the use of percussive drilling in coal or cinder is removed.
All this is backed by cores at 10m spacing – any small pockets of gas will be small and confined to areas between these cores – and is managed by the controls around Zone B and C.
The absence of cores in the right location is taken to be Zone D (high-high) cores and no slotting or percussive drilling in coal or cinder is allowed.
Where the cores on either side of the dyke are in different zones – the ability to mechanically cut a slot is determined by the cores on the side where the slot will be cut. This has required the use of reversing the hand of the mechanical slotter to facilitate slotting on the low gas side.
Given the complex geology of the area, the dyke is inspected by a geologist at least once a week – this confirms the presence and the location of secondary structures and allows the correct placement of cores so that they are positioned in a zone that will be between the dyke and any secondary structure that may be present.
Using these controls – there have been no outbursts that have been unexpected. That is, outbursts that have occurred have occurred on shotfiring with nobody at the face, and have occurred either when gas contents are above threshold or there have been insufficient cores to accurately determine gas content is below threshold.
Russell Thomas, Gas Drainage Coordinator - Appin Colliery, November 2014

5. Analysis of Outbursts during Dyke Extraction
Multiple outbursts at approx 10-16m3t-1 during shotfiring
No outbursts below Appin’s Outburst threshold
All reasonably small outbursts
Based on this experience, it appears the current Outburst Threshold Appin use is appropriate
Reviewing where the outbursts have occurred in the dyke (refer to graph), it can be seen that no outbursts have occurred below Appin’s outburst threshold – so this experience reinforces that the threshold being used by Appin is appropriate. The fact that we have been able to identify areas that may outburst and have put in controls to manage the risk highlights that the combination of understanding the gas regime, understanding the stress environment, and understanding the geology of an area are key to managing the outburst risk.
Further, it appears that the outbursts triggered by shotfiring are occuring at slightly lower levels than outbursts that have been triggered by remote mining. The Gas Drainage Coordinator suspects there may be a slightly different mechanism (or at least a modification of the mechanism around a CM face) at play due to speed of stress redistribution around the face when shotfiring compared to cutting with a CM, but there is not enough evidence of analysis to confirm this yet.
Russell Thomas, Gas Drainage Coordinator - Appin Colliery, November 2014

6. Alteration to Outburst Management Plan
Appin & West Cliff amalgamation is getting close – first roadway from West Cliff to Appin holed during November 2014
Appin & West Cliff have different ways of managing the outburst risk – each evolving of time based on the circumstances of the mine
Process undertaken to review the processes at each mine and use “best practice” in each area.
With available longwall blocks at West Cliff being almost exhausted, much work has been going on at Appin to prepare a second longwall at Appin to replace the West Cliff longwall. Appin and West Cliff will eventually combine to form Illawarra Coal’s Bulli Seam Operations (statutarily West Cliff will become part of Appin).
The first roadways connecting the mines holed during November 2014, and the completion of longwall extraction at West Cliff and commencement of the second longwall at Appin is scheduled for mid 2016.
As part of the amalgamation of Appin and West Cliff, all management plans are being reviewed – including the outburst mgt plan.
This review has very clearly identified that Appin and West Cliff have very different ways of managing the outburst risk. Both plans evolved from a similar starting point in the mid-1990’s but each has evolved to a very different place now.
As such, a process was undertaken over approx 9 months to review both plans and determine what is “best practice”, and determine what is the best outburst management philosophy moving forward.
Artwork Courtesy Iain Brown
Russell Thomas, Gas Drainage Coordinator - Appin Colliery, November 2014

7. Comparison of Outburst Management at Appin and West Cliff
Comparing Appin & West Cliff Outburst Management Practices (Core location, Hole Patterns, Thresholds) revealed 15x gas regimes.
Appin & West Cliff practice approximately the same outburst management techniques in 3 of these (including undrained areas which are not normally mined)
Appin & West Cliff practice different outburst management techniques in 12 gas regimes.
Outburst Management techniques used in each regime at each pit were compared and evaluated against the risk at Appin, and best practice determined.
Multiple stages of consultation undertaken, including workforce reps, and Appin & West Cliff gas drainage personnel. Steps included:
Initial review by Appin Gas Drainage dept
Full review by Outburst Risk Review Team
Review by Appin HSEC committee
Shift briefings to workforce
Risk assessment on proposed changes
More Shift briefings to workforce
Final review by General Manager, Manager of Mining Engineering and Site Check Inspector
The plot in this slide shows the overall threshold plots for Appin and West Cliff (threshold plots of coring and flanking as well as threshold). The areas highlighted blue are areas where both Appin and West Cliff do the same thing. The areas highlighted in red are areas where Appin and West Cliff manage outbursts differently.
It can be seen that there are three areas (including very high gas contents where neither mine would mine normally) that both mines do the same thing. There are 12x areas where we do things differently.
A number of review stages were undertaken to determine best practice, which included multiple stages of consultation, including:
An initial review by Appin’s Gas Drainage Department
Full review by the Outburst Mgt Team, including representative from West Cliff’s Outburst Mgt team to explain the details of how things work at W/C. This produced a recommendation.
Then a review by the Appin HSEC committee of the recommendation from the Outburst Risk Review Team.
Then shift briefings to the workforce
The a risk assessment reviewing the recommendation
The more shift briefings to the workforce
Then a final review by the General Manager, Manager of Mining Engineering, and the Site Check inspector before implementing.
Russell Thomas, Gas Drainage Coordinator - Appin Colliery, November 2014

8. The case to raise thresholds?
Both Appin and West Cliff use a threshold of approx 9.4m3t-1 (100% CH4) / 6.0m3t-1 (100% CO2)
Above this threshold – West Cliff has a “Level 2” threshold of 10.0m3t-1 (100% CH4) / 7.8m3t-1 (100% CO2)
Gas Contents that Appin has remote mined on indicate that little mining falls within this range
Where mining falls within this range, it is generally just the edge of remote mining – with the bulk of the remote mining well above the West Cliff Level 2
Drainage at Appin has tended to be either a spectacular failure or a complete success.
Areas where drainage has failed are generally due to inability to drill and drain around structures
Mining between Appin threshold and West Cliff Level 2 threshold requires heavy use of flanking holes through structure – where drainage has failed due to structure this would not be practicable
Dyke extraction experience indicates the current threshold is appropriate
As such, it was determined there was no case to attempt to raise Appin’s threshold
One of the most obvious differences between the Appin and West Cliff plan is the different threshold in place. Both mines mine normally up to the 9.4m3/tCH4-6.0m3/tCO2 threshold. However, West Cliff has a second threshold that allows mining up to 10m3/tCH4-7.2m3/tCO2 under very certain conditions, with additional controls – mainly flanking holes to provide greater assurance regarding the geological environment.
Reviewing the gas contents that Appin has remote mined on (see graph) indicates that if Appin did use a second threshold, it would only slightly reduce the need to remote mine – most cores taken between the Appin threhsold and WC L2 threshold are basically the edge of remote mining, and the use of a higher threshold would bring in the edges of remote mining a couple of metres.
Further, the remote mining areas are generally areas that Appin cannot drill due to complex structures – so the lack of drilling has led to an obvious lack of drainage. This tends to make drainage at Appin a dazzling success or a dismal failure. So using a higher threshold wouldn’t really help in areas above threhsold. Further, the additional controls required to mine up to the L2 threhsold are not really practicable in an area we couldn’t drain because we couldn’t drill – if we can’t drill an area to drain, how could we drill the required flank holes to be sure of structure.
Further, experience in remote mining and dyke extraction indicates that the complex geology and stress environment at Appin is better suited to a slightly lower threshold.
That is, there is a weak business case to devote the reosurces that would be required to justify a raising of Appin’s threshold, and the technical case behind it, looks weak as well.
Russell Thomas, Gas Drainage Coordinator - Appin Colliery, November 2014

9. Final Outcome The final outcome is shown here.
A simplified outburst threshold.
Russell Thomas, Gas Drainage Coordinator - Appin Colliery, November 2014

10. Russell Thomas, Gas Drainage Coordinator - Appin Colliery, November 2014