Coal Gas

CoalGAS awarded an ACARP Project

Dennis Black — Sun, 14 Apr 2019 06:49:13 +0000

CoalGAS has been awarded an ACARP Project (C28007) to investigate the impact of core sample recovery time on accuracy of gas content measurement

It is generally accepted in core sample gas content testing in Australian underground coal mines that a “correction factor” is added to the measured gas content when the time to recover the core sample from the coal seam exceeds 40 minutes. The addition of the measured gas content and the correction factor amounts to the reported gas content (QM) provided to coal mines.

For mines that require the use of gas drainage to reduce gas content below defined outburst threshold limits (OBTLV), the addition of the correction factor may cause the reported gas content value to be greater than the OBTLV. In such cases, these mines are required to further reduce gas content and retest the area to confirm the gas content (reported gas content) has been reduced below the OBTLV prior to the area being approved for mining, in accordance with the mine’s Permit to Mine approval process. The potential impact of delays to achieve gas content compliance for a mining area may cause delays to mine development operations while additional work, such as increased gas drainage drilling, extended gas drainage time and additional core sample collection and gas content testing, is carried out to reduce gas content and confirm the gas content has been reduced below OBTLV.

CoalGAS has completed some initial testing at one mine that shows recovery time has minimal impact on the accuracy of gas content measurement. This is a potentially significant finding that suggests the addition of the gas content correction factor is unnecessary and may overstate the gas content in the area where the coal sample was collected.

With support from ACARP, CoalGAS plans to expand the testing program to carry out similar tests in a broad range of Australian coal seam conditions. All Australian coal mines that employ underground-to-inseam (UIS) drilling to pre-drain coal seam gas prior to mining are invited to participate in this study.

What do you get?

Site specific assessment of the impact of core sample recovery time on gas content accuracy;
Potential to avoid the addition of a gas content correction factor to reported gas content values;
Potential to avoid a situation where measured QM is below OBTLV and the addition of the gas content correction factor causes the reported QM value to be greater than the OBTLV

What does it cost?

Mines participating in this study will be required to undertake a program of core sample collection and testing in accordance with a standard testing program defined by CoalGAS;
The test program requires a series of core samples to be collected from a UIS borehole that are tested to determine the impact of extended core sample recovery time on the accuracy of gas content measurement.

Want to participate?

For more information and to find out how your mine can participate and benefit from this study, contact Dennis Black via Email: db@coalgas.com.au or Mobile: 0401999542

Coal Seam Gas Drainage

sarah — Tue, 20 Mar 2018 04:33:08 +0000

Coal Seam Gas Drainage – Improving performance

Gas drainage systems in underground coal mines often fail to deliver the planned / expected gas production rates and subsequently fail to reduce the gas content of the coal seam within the scheduled timeframe.

Underperforming and ineffective gas drainage can result in delays to mine production due to high residual gas content (above outburst threshold limits), or methane gas concentrations in the ventilation system that exceed statutory limits. When faced with such conditions it is a common response from mine operators to drill more boreholes in the area (over drilling the area) which not only increases operating cost but also affects the drilling schedule as drill rigs are diverted away from scheduled works. In extreme cases, mine plans have been altered to avoid ‘difficult-to drain’ areas which reduces coal reserves and shortens mine life.

It is important that those responsible for the design and management of gas drainage systems understand the geological factors that must be considered in the initial design and the operational factors that impact gas drainage performance. Geological conditions vary between mines and often change significantly over short distances within the bounds of a mining lease. It is necessary to collect sufficient detail to understand the geological setting and the potential effect on gas drainage design.

Prevailing geological conditions, whilst unable to be changed, should be considered to design gas drainage programs that maximise gas production potential within those set constraints. The operational factors, if understood and managed effectively, can significantly affect gas drainage performance within the limitations imposed by the prevailing geological conditions. Significant operational factors that should be considered in the design and ongoing monitoring and management of gas drainage systems are listed in the table below.

The control and ongoing maintenance of gas drainage boreholes and gas reticulation pipelines, specifically the removal of water and coal fines, has arguably the greatest impact on gas drainage performance. I often find mines have going to significant effort and expense to design and implement gas drainage however failing to remove water accumulations from the boreholes and the pipe range which significantly reduces gas production. The design of gas drainage boreholes and gas reticulation networks should provide for the effective separation and removal of both gas and water. The presence of water in boreholes impedes gas desorption, and water accumulation in gas reticulation pipes/hoses increases resistance and reduces the effective gas carrying capacity of the system. Downhole water removal, standpipe design and water separators should be incorporated into the gas drainage system. The performance of the system should be regularly checked and maintained, as often as necessary, to clear water and fines accumulation.

References:

Black, D J, 2011. Factors affecting the drainage of gas from coal and methods to improve drainage effectiveness, PhD thesis, University of Wollongong. p.384.

Black, D J and Aziz, N I, 2011. Actions to improve coal seam gas drainage performance, in Proceedings of the 2011 Underground Coal Operators Conference, University of Wollongong, Wollongong, 10-11 February, pp. 309-316.

Black, D J and Aziz, N I, 2010. Impact of coal properties and operational factors on mine gas drainage, in Proceedings of the 2010 Underground Coal Operators Conference, University of Wollongong, Wollongong, 11-12 February, pp 229-240.

Black, D J and Aziz, N I, 2008. Improving UIS gas drainage in underground coal mines, in Proceedings of the 16th Coal Congress of Turkey, Chamber of Mining Engineers of Turkey, Zonguldak, Turkey, 26-28 May, pp 157-170.

Contact:

For further information or assistance with design, audit and improvement of coal mine gas drainage system performance, contact CoalGAS.

Presenting at the Coal Operators Conference 2018

sheen — Wed, 17 Jan 2018 04:41:13 +0000

Presenting at the Coal Operators Conference 2018

The 2018 Coal Operators Conference is being held on 7-8 February 2018 in Wollongong. The conference, has been held by the Mining and Engineering Group of the Faculty of Engineering and Information Sciences, University of Wollongong, since 1998. The conference is supported by the Illawarra Branch of The Australasian Institute of Mining and Metallurgy (AusIMM) and the Mine Managers Association of Australia (MMAA).

The conference aims to address issues related to various aspects of modern coal mining operations, both surface and underground and offers the opportunity for industry experts to share advice and insights in this area.

Dennis, from CoalGAS, is pleased to be presenting on his recent investigations into the use of the DRI method ( Desorption Rate Index ) to determine outburst threshold limits for Australian underground coal mines. Book your tickets now and come and meet the team.

ABSTRACTS

Title: Analysis of Bulli Seam Benchmark and DRI to determine outburst threshold limits

Abstract: Following the introduction of the Desorption Rate Index (DRI) and Bulli Seam Benchmark to the Australian coal industry in 1995, the use of the DRI900 method was adopted and continues to be used as the primary method to assess outburst risk and to determine gas content threshold values for outburst risk management in Australian coal seams. In addition to assessing outburst risk based on gas content threshold values, several Australian coal mines also include DRI900 as a threshold level in assessing outburst risk. It is apparent that there is a broad lack of awareness and understanding of the limitations and deficiencies of using DRI to assess outburst risk and to determine appropriate outburst threshold limit values.

A comprehensive set of gas test results from Australian coal seams has been collected as part of research into control and management of outburst risk in Australian underground mines and the results of specific investigation into DRI and its applicability for use in assessing outburst risk and determining appropriate gas content threshold levels has identified significant deficiencies which are presented and discussed.

Title: Control and management of outburst in Australian underground coal mines

Abstract: Outbursts represent a major safety hazard to mine personnel working near the coal face in areas of increased outburst risk. There have been over 878 outburst events recorded in twenty two Australian underground coal mines and most outburst have been associated with abnormal geological conditions.

Details of Australian outburst incidents and mining experience in conditions where gas content was above current threshold levels is presented and discussed. Mining experience suggests that for gas content below 9.0 m 3 /t, mining in CO2 rich seam gas conditions does not pose a greater risk of outburst than mining in CH4 rich seam gas conditions.

Mining experience also suggests that where no abnormal geological structures are present, mining in areas with gas content greater than the current accepted threshold levels can be undertaken with no discernible increase in outburst risk.

The current approach to determining gas content threshold limits in Australian mines has been effective in preventing injury from outburst however operational experience suggests the current method is overly conservative and in some cases the threshold limits are low to the point that they provide no significant reduction in outburst risk.

Other factors that affect outburst risk, such as gas pressure, coal toughness and stress and geological structures are presently not incorporated into outburst threshold limits adopted in Australian mines. These factors and the development of an Outburst Risk Index applicable to Australian underground coal mining conditions is the subject of ongoing research.

Find out more about the Coal Operators Conference

How to Reduce Gas-Related Production Delays

sheen — Wed, 17 Jan 2018 04:30:48 +0000

How to Reduce Gas-Related Production Delays

Gas-related production delays can be reduced through gas reservoir modelling and emissions forecasting to support gas drainage design.

The process of excavating and mining coal causes fractures in the overlying and underlying strata. The fractures provide pathways for gas released from coal seams and other gas-bearing strata to flow into the mine workings. Coal seam gas typically contains high concentrations of methane with lesser concentrations of carbon dioxide. Low concentrations of other gases such as nitrogen, hydrogen sulphide and ethane may also be present in some coal seams. In certain geological settings, particularly in close proximity to geological structures, such as faults and dykes, the concentration of gases contained in a coal seam can vary significantly between methane-rich to carbon dioxide-rich.

In mine design and planning it is vital that mining engineers gather sufficient information to accurately determine the content and composition of the gas present in the coal seam and develop an understanding of changes in these parameters within the planned mining area.

The longwall method of mining coal causes fracturing of the overlying and underlying strata behind the retreating longwall face. Where coal seams and other gas-bearing strata are present within the caving zone, gas will be released from the strata leading to contamination of the mine workings. If the rate of gas emission exceeds the diluting capacity of the mine ventilation, the concentration of gas in the mine may exceed the statutory limit, resulting in production delays and potentially unsafe conditions.

The frequency of gas concentrations in ventilation air exceeding the defined statutory limit has increased, in part due to reduced expenditure on gas drainage but often due to a lack of understanding of the strata, gas reserves and gas emission potential into the mine workings. This results in development and production delays and avoidance of ‘difficult-to-drain’ areas. It is apparent that many operations are not effectively utilising gas reservoir and emission modelling to identify high gas emission areas and are not completing sufficient gas drainage in advance of planned mining. These production delays result in significant economic impacts.

The process of gas reservoir and emission modelling, in conjunction with the design of efficient and effective gas drainage, is an essential component of the mine planning process to control tailgate gas concentrations, reduce gas-related production delays, reduce fugitive emissions and ensure the continued economic success of your project.