ISO 18871:2015

Method of determining coalbed methane content

ISO 18871:2015 provides methodology for measuring coalbed methane content of coal core samples obtained by coring or sidewall coring during well drilling. It shall be also applied to drill cuttings samples, if the equipment for the determination of the coalbed methane content according to a respective national standard is not available. The selection of the most appropriate method shall consider the purpose of the test and the possibilities of sampling. ISO 18871:2015 is applicable for the direct method of measuring coalbed methane content. It includes sample preparation, experimental procedures and calculation methods. Indirect methods of measuring gas content of coal (not included in this standard) are generally based on either the gas sorption characteristics of coal under defined/specified pressure and temperature conditions. ISO 18871:2015 includes three types of direct measuring methods: conventional desorption (slow desorption) of core samples, fast desorption of core samples, fast desorption of cuttings or lump samples. The difference among them lies in the time allowed for gas to desorb before final crushing and in sample size and shape. ISO 18871:2015 is applicable for the determination of the methane content of coal during coal and coalbed methane exploration for the determination of free gas content of low rank coals is included.

Méthode de dosage de la teneur en méthane de houille

General Information

• Status: Published
• Publication Date: 28-Sep-2015
• ICS: 73.020 - Mining and quarrying
• Technical Committee: ISO/TC 263 - Coalbed methane (CBM)
• Drafting Committee: ISO/TC 263 - Coalbed methane (CBM)
• Current Stage: 9093 - International Standard confirmed
• Completion Date: 05-Aug-2021

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 18871
First edition
2015-09-15
Method of determining coalbed
methane content
Méthode de dosage de la teneur en méthane de houille
Reference number
ISO 18871:2015(E)
©
ISO 2015

---------------------- Page: 1 ----------------------
ISO 18871:2015(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2015, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. [phone]
Fax [phone]
[e-mail]
www.iso.org
ii © ISO 2015 – All rights reserved

---------------------- Page: 2 ----------------------
ISO 18871:2015(E)

Contents Page
Foreword .v
1 Scope . 1
2 Terms and definitions . 1
3 Apparatus . 3
3.1 Desorption canister . 3
3.2 Metering device . 3
3.3 Thermostat . 5
3.4 Temperature measuring devices . 5
3.5 Barometer . 5
3.6 Electronic balance (top load) . 5
3.7 Standard sieve . 5
3.8 Coal crusher . 5
3.9 Hose . 6
3.10 Gas-sample bottles . 6
3.11 Padding . 6
3.12 Quick connector . 6
3.13 Gas analyser . 6
4 Sample collection . 7
4.1 Preparation of sampling . 7
4.1.1 General. 7
4.1.2 Desorption canister . 7
4.1.3 Metering device. 7
4.1.4 Thermostat . 7
4.2 Sampling principle . 7
4.2.1 Sample quality . 7
4.2.2 Sampling time . 8
4.3 Sampling procedure . 8
4.3.1 General. 8
4.3.2 Core samples . 8
4.3.3 Cutting samples . 8
4.4 Coal lump samples . 8
4.4.1 General. 8
4.4.2 Parameters to record . 8
5 Measuring method and process . 9
5.1 Use of core samples . . 9
5.1.1 Natural desorption . 9
5.1.2 Measurement of residual gas .10
5.1.3 Gas sampling, composition analysis and isotope analysis .10
5.2 Use of cuttings samples or coal lump samples .12
5.2.1 Q2 measurement . . .12
5.2.2 Q3 measurement . . .12
6 Data processing .13
6.1 Conversion of the desorbed gas volume .13
6.2 Reporting of gas content .13
6.3 Calculation of gas composition .13
6.4 Calculation of gas content .13
6.4.1 General.13
6.4.2 Calculation of lost gas content (Q1) .13
6.4.3 Calculation of gas desorption content (Q2) .15
6.4.4 Calculation of residual gas content (Q3) .15
6.4.5 Calculation of free gas content .16
6.4.6 Calculation of gas content .16
© ISO 2015 – All rights reserved iii

---------------------- Page: 3 ----------------------
ISO 18871:2015(E)

6.4.7 Calculation of adsorption time .17
6.5 Numerical accuracy requirements .17
7 Measurement report .17
8 Quality commentaries .17
8.1 Quality commentary of sample collection .17
8.1.1 Situations should be noted on the record .17
8.2 Quality commentary on measuring operation .18
8.3 Conclusion of quality commentary .18
8.3.1 Qualified samples .18
8.3.2 Reference samples .18
8.3.3 Discard .18
Annex A (normative) Raw data of gas natural desorption .19
Annex B (normative) Lost gas original records table.21
Annex C (normative) Lost gas volume calculation of Sample XX (direct method) .22
Annex D (normative) Cumulative gas desorption curve of sample XX .23
Annex E (normative) Measurement results table of CBM content .24
Annex F (normative) Sampling form for in-seam drilling .25
Annex G (normative) Sampling form for core drilling .26
Annex H (normative) Laboratory test form.27
Annex I (normative) Short report .28
Bibliography .29
iv © ISO 2015 – All rights reserved

---------------------- Page: 4 ----------------------
ISO 18871:2015(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2. www.iso.org/directives
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received. www.iso.org/patents
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical
Barriers to Trade (TBT), see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 263, Coalbed methane (CBM).
© ISO 2015 – All rights reserved v

---------------------- Page: 5 ----------------------
INTERNATIONAL STANDARD ISO 18871:2015(E)
Method of determining coalbed methane content
1 Scope
This International standard provides methodology for measuring coalbed methane content of coal
core samples obtained by coring or sidewall coring during well drilling. This standard has to be also
applied to drill cuttings samples, if the equipment for the determination of the coalbed methane content
according to a respective national standard is not available. The selection of the most appropriate
method shall consider the purpose of the test and the possibilities of sampling.
This International standard is applicable for the direct method of measuring coalbed methane content.
It includes sample preparation, experimental procedures and calculation methods. Indirect methods of
measuring gas content of coal (not included in this International standard) are generally based on either
the gas sorption characteristics of coal under defined/specified pressure and temperature conditions.
This International standard includes three types of direct measuring methods: conventional desorption
(slow desorption) of core samples, fast desorption of core samples, fast desorption of cuttings or lump
samples. The difference among them lies in the time allowed for gas to desorb before final crushing and
in sample size and shape.
This International standard is applicable for the determination of the methane content of coal during coal
and coalbed methane exploration for the determination of free gas content of low rank coals is included.
Procedure of free gas content determination of low rank coals need to be defined.
All units used and referred to in this International standard are international standard units. Reference
temperature is 0 °C (273,15 K) if not stated differently. Reference pressure is 0,1 MPa (1 bar) if not
stated differently.
This International standard does not point out all the potential safety hazards associated with its use.
The users are responsible for establishing appropriate safety measures and health practices when
applying the procedures defined in this standard.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1
coalbed gas content
under natural conditions, quantity of gas contained in the unit mass of coal
Note 1 to entry: It is the sum of lost gas, measurable gas and residual gas.
2.2
coalbed methane content
methane content, which is commonly the major component of coalbed gas
Note 1 to entry: The terms “coalbed methane”, “coalbed gas” and “coal seam gas” are frequently used
synonymously.
Note 2 to entry: If a component other than methane is the predominant component of coalbed gas this should be
stated explicitly.
© ISO 2015 – All rights reserved 1

---------------------- Page: 6 ----------------------
ISO 18871:2015(E)

2.3
Q1 (lost gas)
gas lost from the samples subsequent to its removal from its in situ position and prior to its containment
in the canister, expressed as volume (at standard conditions) per unit mass of coal
2.4
Q2 (measurable gas)
measurable gas desorbed at atmospheric pressure from the non-pulverized coal sample, expressed as
the quantity per unit mass of coal
2.5
Q3 (residual gas)
gas still contained in the coal sample before its pulverisation, expressed as the quantity per unit mass
of coal
2.6
conventional desorption (slow desorption)
method of gas determination in which volumetric readings of canister gas content are taken frequently
(every 5 min) during the first few (2 to 6) h, followed by hourly measurements for several hours, and then
measurements on 24-h intervals until no or very little gas is being desorbed for an extended period of time
2.7
fast desorption
method of gas content determination in which a trend of gas desorbing from the coal sample is not
established
Note 1 to entry: Measurements are taken over a period of time typically less than 1 day
2.8
sampling
activity that take some representative part of coal from coalbed
2.9
core sample
cylindrical section of rock (coal) that is usually 5 cm to 10 cm in diameter taken as part of the interval
penetrated by a core bit and brought to the surface for geological examination, representative sampling,
and laboratory analysis
2.10
cuttings sample
rock (coal) fragments, chips, particles with a size of typically ≤5 mm that break off because of the action
of the drill bit and are transported to the surface by the drilling circulation system
2.11
coal lump samples
coal fragments or pieces of coal fragments that break off in the extraction or development process of
a coal mine operation, from coal transport or storage or by manual removal from the coal seam or an
intact core sample. The size is larger than that of cuttings and smaller than the inner diameter of the
canister used for transportation and desorption
2.12
low-rank coal
the coal and rock thermal evolution degree is low, vitrinite of oil-immersed maximum reflectance
R ≤ 0,65%, including lignite and long flame coal
v,max
[SOURCE: ISO 11760:2005]
2.13
high-rank coals
coal and rock thermal evolution degree is high, vitrinite of oil-immersed average random reflectance
R ≥ 2,0%, including anthracite coal
r
2 © ISO 2015 – All rights reserved

---------------------- Page: 7 ----------------------
ISO 18871:2015(E)

3 Apparatus
3.1 Desorption canister
The desorption canister is a sealable container into which the coal samples are placed to determine
their gas content. The canister should be designed such that the coal can be transferred into a pressure-
tight status as quickly as possible.
Canisters should be easy to handle and fill and should close rapidly to form a gas sealed space.
The material of the canister shall not absorb coalbed gas, or react with drilling fluid and coalbed
gas. Therefore, it is recommended to use aluminium alloy, coated aluminium, PVC and/or stainless
steel materials.
3
When using core samples, the canister volume shall be more than 1 000cm with a suitable inner
diameter. It should maintain gas tightness up to a pressure of 0,3 MPa.
3
When using cuttings samples or coal lump samples, the canister volume shall be ≥ 500 cm . The ratio
of canister volume and sample volume shall be between 70 and 150. The desorption canister shall
be equipped with a shut-off valve and a rubber hose to connect it to a gas metering device and gas
analyser (Figure 1).
Key
1 squeezing device
2 desorption canister
3 hose
4 flowmeter
5 gas analyser
Figure 1 — Desorption canister with connection to gas analyser
3.2 Metering device
The measurement of desorbed gas volumes shall be executed either by the displacement of water
(displacement method) or by flushing the crusher head with a defined volume of air and subsequent
analysis of the gas composition (flushing method).
For the displacement method, a graduated measuring cylinder (burette) is used. The volume and scale
of the measuring cylinder shall be appropriate to the desorption volume. The measuring cylinder and
storage reservoir are preferably of glass. Readings of the gas volume are taken at atmospheric pressure
by adjusting the liquid levels in the tube and the storage cup. The minimum graduation on the metering
3
scale shall be no more than 10 cm . The measuring cylinder is connected at the bottom to a storage
© ISO 2015 – All rights reserved 3

---------------------- Page: 8 ----------------------
ISO 18871:2015(E)

reservoir and at the top to the desorption canister head. The connections shall be made of flexible and
gas-tight plastic or rubber.
Key
1 desorption canister
2 hose
3 graduated cylinder
Figure 2 — Desorption canister with graduated cylinder for collection of desorbed gas
Key
1 desorption canister
2 hose
3 burette
4 storage reservoir
Figure 3 — Desorption canister with graduated burette and storage reservoir for pressure
equilibration
4 © ISO 2015 – All rights reserved

---------------------- Page: 9 ----------------------
ISO 18871:2015(E)

For the flushing method, a defined volume of air is passed through the crusher headspace and collected
in a vessel, preferably of glass. The collecting vessel shall be connected to the gas analyser [see 3.13] by
a flexible hose. The connections shall be flexible and gas tight plastic or rubber.
3.3 Thermostat
A water, oil or air thermostat shall be used with a temperature stability and controlling accuracy of ± 1°C.
3.4 Temperature measuring devices
Temperature should be measured with an accuracy of 1°C or better. The temperature range of the
measuring devices (thermometer, thermocouple, resistance thermometer) should cover both the
ambient temperature and the temperature in the thermostat holding the desorption canisters. Typically
this should correspond to a range from 10 °C to 80 °C.
3.5 Barometer
The measurement range of the barometer for metering the ambient pressure should cover the local
range of ambient pressure. Scale intervals should be 0,1 kPa.
3.6 Electronic balance (top load)
A precision (accuracy ± 1 %) electric, top-load balance with appropriate capacity is used to weigh empty
and filled canisters.
3.7 Standard sieve
The sieve shall be 60 mesh (maximum grain size 2 mm)
3.8 Coal crusher
A coal crusher is required for pulverization of the coal in order to release all remaining gas rapidly.
For conventional desorption test, samples are completely broken during the residual gas test in the
measurement process.
In case of using the displacement method, the crusher shall be gas tight and equipped with an adapter
for connecting a rubber or plastic hose to transfer gas to the metering device (Figure 4). The crusher
headspace shall be minimized.
In case of using the flushing method, the tightness of the crusher shall be adjusted to the flushing
process. The gas being released during crushing shall be mixed with inflowing air completely with all
mixed gas being captured in the collecting vessel.
© ISO 2015 – All rights reserved 5

---------------------- Page: 10 ----------------------
ISO 18871:2015(E)

Key
1 coal crusher
2 hose
3 burette
4 storage reservoir
Figure 4 — Coal crusher with graduated burette and storage reservoir for pressure
equilibration
3.9 Hose
The hose material shall not adsorb coalbed methane and not react with it.
3.10 Gas-sample bottles
Gas-sample bottles are used for collecting samples for subsequent analysis. The volume of the gas-
3
sample bottle shall not be less than 100 cm
3.11 Padding
Cylinders, glass spheres and hollow tubes are used to reduce the void volume of the desorption canister.
These should be made of materials not adsorbing coalbed methane and not reacting with coalbed methane.
3.12 Quick connector
Quick connector is a pipe fitting designed for easy and rapid connection and disconnection.
3.13 Gas analyser
The gas analyser shall be equipped with sensors for the main components of the adsorbed gas, at least
with a sensor for methane, preferably an infrared sensor. The accuracy of the analyser shall be ± 5 % of
the measured value or better.
6 © ISO 2015 – All rights reserved

---------------------- Page: 11 ----------------------
ISO 18871:2015(E)

4 Sample collection
4.1 Preparation of sampling
4.1.1 General
3
The container [3.1] volume shall be above 1 000 cm , and its diameter shall be suitable for coal cores,
and maintain gas tightness under pressure of 0,3 MPa. The material of the container shall not absorb
coalbed methane, or react with drilling fluid and coalbed methane. Therefore, it is recommended to use
aluminium alloy, coated aluminium, PVC and stainless steel materials.
4.1.2 Desorption canister
All desorption canisters (3.1) for measuring coalbed methane content shall pass an air tightness test
before use. For this test the desorption canister shall be pressurized with air to a pressure of 0,3 MPa.
The canister is usable if the pressure does not drop by more than 0,001 MPa within 12 h.
4.1.3 Metering device
Before use, the metering device shall be filled with water and initialized to check its air-tightness
and performance.
4.1.4 Thermostat
Before filling the coal samples into the canister for the desorption test, the thermostat shall be
adjusted to the reservoir temperature. Sufficient time shall be allowed for the thermostat to stabilize
at this temperature.
4.2 Sampling principle
4.2.1 Sample quality
4.2.1.1 Sample quality of core samples
The mass of coal sample placed into a canister shall not be less than 800 g.
If coal core recovery is not sufficient but the measurement is still required, the minimum sample mass
shall not be less than 300 g and only desorption gas could be measured in this situation. This fact shall
be explicitly stated in the report.
4.2.1.2 Requirements for cuttings samples and coal lump samples
For samples from in-seam drilling, cuttings with a defined grain size, preferably ≥ 2mm shall be taken
from the outbye end of the borehole without mixing coal from different positions within the borehole.
Cuttings and lump samples shall have a mass of about 10 g. The actual mass of the coal sample shall be
appropriate to the
...