[sub heading] [date] 13 th Longwall Conference 2014, Hunter Valley 27 th -28 th October Shoba Keys, Guy Mitchell
[sub heading] [date]
13th Longwall Conference 2014, Hunter Valley 27th -28th October
Shoba Keys, Guy Mitchell
Introduction
Slide 2
To optimise production and safety objectives, early understanding of the
size and extent of gas emissions is required through:
Acquiring quality data from gas testing samples as input to:
Reservoir assessment and
Models for gas emissions, allowing
Timely planning and implementation of gas management strategies,
and
Monitoring, review and refinement.
Introduction
Slide 3
Understanding the size and extent of gas emissions leads to:
Potentially cheaper but correct implementation of solutions,
Reduction in safety risk,
Increased productivity,
Lower cost, larger profit margin, and
Job security.
Conduct a risk assessment to determine the impact of lost tonnes to
costs, as a result of limited understanding of the gas reservoir and
emissions.
The next few slides
Slide 4
Trends for mines and projects.
Challenges for mines and projects.
Reservoir assessment
Reservoir properties
Qld and NSW Coalfields
Slide 5
Production
from longwall
mines
increased
33%, or
22Mtpa in 13
years.
Trend for Mines
Slide 6
Towards longer panels, wider faces, greater extraction heights and
increased production rates.
Increasing depth of mine workings resulting in higher seam gas contents
combined with lower in situ permeability.
Mine ventilation is increasingly unable to meet statutory limits relating to
CH4 or CO2 levels.
Excess gas emissions can only be controlled through gas drainage
and gas capture techniques to allow operation within statutory limits at
planned development and production rates.
Challenges for Mines and Projects
Slide 7
To understand the size and capacity of the gas reservoir (ie reservoir
characterisation), in a timely manner to allow planning and investment
decisions to be made and implemented.
Acquisition of quality data is essential.
Knowing the time required for drainage.
This may take a relatively long time to effect, with gas drainage times
normally in the range of months to years.
Reservoir Assessment
Early understanding of the size and extent of gas emissions that may
impact on development and longwall production.
Well designed and relevant gas management strategy.
Time to execute the plan, monitor and review. (PDCA cycle).
Execute necessary changes in a more controlled and deliberate
manner.
Slide 8
Gas Content Gradients Mapped as Domains
Slide 9
0 100 200 300 400 500
Depth below surface (m)
Mea
su
red
ga
s co
nte
nt
(m3
/t at
15%
Ash
)
Domain 1
Domain 2
Domain 3
DomainExample.xls Domains
0 100 200 300 400 500
Depth below surface (m)
Mea
su
red
ga
s co
nte
nt
(m3
/t at
15%
Ash
)
Domain 1
Domain 2
Domain 3
DomainExample.xls Domains
A quality validated data set allows variability across mine lease areas to
be identified.
Understand Gas Emissions by Timely Data Capture
Slide 10
Additional Properties for Gateroad
• Gas sorption capacity at reservoir
temperature
• Pore pressure
• Coal porosity and compressibility
Additional Properties for Longwall
• Distances of gas sources from worked seam
• Gas desorption pressure
• Non coal strata gas
• Non coal rock porosity
• Faulting and other geological discontinuties
Properties Common
to Gateroad and
Longwall
• Gas content and
composition
• Gas desorption rate
• Seam thickness
• Permeability
Permeability Regional Variation in Sydney / Bowen Basins
Slide 11
0.0
0.1
1.0
10.0
100.0
1000.0
0 50 100 150 200 250 300 350 400 450
Depth (m)
Pe
rme
ab
ilit
y (
mD
)
Allperm.xls
Typically there is
insufficient
investment in
obtaining
permeability
data. Improved
understanding
leads to good
assumptions
and better
design for gas
drainage. Think about spending a little bit of money earlier to
avoid spending heaps more later in a lost
production stress situation, avoid “too little, too late”.
Gas Reservoir Size (GRS) Variations
Slide 12
Understanding the variation in gas reservoir size is key to spending
the right amount for gas management – not over or undersized.
Av GRS
84m3/m2
Av GRS
6m3/m2
Benefits
Slide 13
Effective reservoir assessment and modelling of emissions leads to
improved cutting hours for the longwall and development.
For example increasing productivity for say
1 hour per day, 7 days per week, for 45 weeks,
results in 315 hours per year.
for a longwall producing an average of 1,800tph, this leads to a
significant increase of potentially up to 567,000t per year (utilisation
dependent).
For a mine producing $3Mtpa, this increases production by 19% to
$3.6Mtpa
Even at the current low sale price of USD$66 per tonne, this is significant
increase in revenue of more than USD$37M. The increased costs for
power, wear and tear and other consumables are small, for 19% more
tonnes.
How to determine Gas Emissions
Slide 14
The next few slides looks briefly at different models.
Determine development emissions by:
• Empirical models
• Gas reservoir simulation
Determine longwall emissions by:
• Flugge models
• Pore pressure models
Determining Development Emissions
Slide 15
Empirical models
Gas reservoir simulation (multi-phase)
Determining Longwall Emissions
Slide 16
Highly complex processes being modelled
Pore Pressure Model
Slide 17
Rear
Abutment
Zone
Front
Abutment
Zone
goaf
faceDirection of travel
Rear
Abutment
Zone
Front
Abutment
Zone
goaf
faceDirection of travel
Rear
Abutment
Zone
Front
Abutment
Zone
goaf
faceDirection of travel
Rear
Abutment
Zone
Front
Abutment
Zone
goaf
faceDirection of travel
Active Gas Zone
Rear
Abutment
Zone
Front
Abutment
Zone
goaf
faceDirection of travel
Rear
Abutment
Zone
Front
Abutment
Zone
goaf
faceDirection of travel
Rear
Abutment
Zone
Front
Abutment
Zone
goaf
faceDirection of travel
Rear
Abutment
Zone
Front
Abutment
Zone
goaf
faceDirection of travel
Active Gas Zone The extent of degassing
above and below the
working seam depends
on pore pressure post
mining and the gas
desorption pressure,
which is dependent on
gas content and
composition.
Requirements include
pore pressure and
isotherms.
Confidence
Slide 18
-0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6
Langmuir
Volume
Gas content
Water Level
from Surface
Langmuir
pressure
Q3
Coefficient Value
DesP&SatUncertainty.xls{Sensitivit
y}
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0.20
30 34 38 42 46 50 54 58 62 66 70 74 78 82 86 90 94 98
Gas Saturation%
Pro
bab
ilit
y
DesP&SatUncertainty.xls{S
aturation}
Gas reservoir assessment, and emission modelling has many inputs.
Understanding their importance to the results determines priorities for data
acquisition.
Conclusion
Slide 19
In the example earlier of increasing productivity by:
1 hour per day for a 45 week period (that is 315 hours),
the outcome for a longwall producing an average of 1,800tph is
significant at potentially up to 567,000t (utilisation dependent).
A pro-active, professional and timely approach to determine gas
emissions by gas testing samples is essential to achieve reduced
production downtime.
The reservoir assessment (quality data acquisition) leading to good
assumptions in models for gas emissions, is significant in working
towards this outcome.