M2 Objectives%2Epdf

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PART-2: CBM EXPLORATION

PROGRAM OBJECTIVES

Dr Alan Bayrak

Managing Director

Coal Seam Gas Exploration & Production Services


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IDENTIFY THE CBM PROSPECTIVITY OF THE POTENTIAL

COAL SEAMS

Definition of prospective coal seam:

A prospective coal seam must hold a certain amount of

recoverable gas with high concentration of methane (95>)

to be extracted economically in current market and

technological conditions.

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Gas composition;

Gas content;

Coal thickness;

Coal Depth;

Permeability; and

Identify potential CBM production zones.

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Gas composition analysis is very

important in assessment of CBM

in coal reservoirs. CBM consists

predominantly of methane (90-

99%) with minor amounts ofother gases like carbon dioxide

and nitrogen.

Inert gases (carbon dioxide and

nitrogen) having content >5% isnot accepted in most of the

pipelines.


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Gas content testing is the most important stage in an

exploration program and needs high quality, reliable data

to evaluate the resource potential of CSG in a prospect

area. Gas content test includes three main gas estimation

stages as follows:

Q1-Lost Gas

Q2-Measurable Gas

Q3-Residual Gas

All measurements must be conducted at reservoir

temperature conditions. Desorption process is a

continuous event and sometimes it takes up to three

months (depends on natural permeability in the coal). It

starts right after coal sample is sealed off in the canister

(at the field) and continues till all gas is released from the

coal (at the lab). In this method, gas content is determined

by collecting and measuring the volume of gas released

from a sample of coal taken out from the coal seam by

drilling.


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Total net coal thickness is an

important parameter in

constraining the CBM resources,

however it is thickness of individual coal seams and their

proximity to each other that affects

the design and cost of the gas fielddevelopment. A minimum of 8-10

metres net coal can be considered a

potential reservoir.


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A practical depth range of

commercial CBM develop-

ments is 250 metres up to

1200metres under favourablepermeability and gas content.


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Total Test

1050

1100

1150

1200

1250

1300

Pressure(psi(a))

0

100

200

300

400

LiquidRate(bbl/d)

-12

-10

-8

-6

-4

-2

0

Error(%)

0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00

Time (h)

pdata

pmodel

qwater

% Error

pi (syn) 1320.8 psi(a)

p*model 1320.8 psi(a)

Cumwater 0.00 MbblW IPmodel Mstb

kh 385.63 md.ft

h 34.449 ft

k 11.1944 md

sd -0.109

Xe ft

Ye ft

Xw ft

Yw ft

Total Test

1050

1100

1150

1200

1250

1300

Pressure(psi(a))

0

100

200

300

400

LiquidRate(bbl/d)

-12

-10

-8

-6

-4

-2

0

Error(%)

0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00

Time (h)

pdata

pmodel

qwater

% Error

pi (syn) 1320.8 psi(a)

p*model 1320.8 psi(a)

Cumwater 0.00 MbblW IPmodel Mstb

kh 385.63 md.ft

h 34.449 ft

k 11.1944 md

sd -0.109

Xe ft

Ye ft

Xw ft

Yw ft

The most critical factor in CSG play is the presence of permeability.Properties of the natural fracture system (cleats) have the greatest

effect on gas and water production rates. Absolute permeability

and relative permeability are two of the most important naturalfracture system flow properties. Permeability of a coal bed is

determined by its fracture (cleat) system, which in turn is largelycontrolled by the tectonic/structural setting. Whilst permeability

testing provides useful information the key for any area is to

demonstrate production from the seams. Permeability testingdetermines the in-situ reservoir permeability of target coal seams

utilis-ing injection/falloff tests, which are very effective andefficient for testing water saturated coal seams.


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Define the composition and content

of the coal seam gas within the coals

attributable to economic gas

production;

Identify potential CBM targets;

To advance the understanding of the

extend of the coal seams;

To incorporate the borehole datainto the database program to

improve geological model for the

area;

To assist in geological correlation ofexisting seismic data in the prospect

area.

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