[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.