ISO 24835-1:2025

ISO/DISPRF 24835-1:2025(en)
ISO/TC 193/SC 3/WG 9
Secretariat: SAC
Date: 2025-07-31
Natural gas upstream area — Determination and calculation of shale
brittleness index —
Part 1:
Determination of shale mineral characteristics based on X-ray
diffraction method
PROOF
ISO/DISPRF 24835-1:2024（2）2025(en)
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© ISO/DIS 24835-1:2024(1)– 2025 – All rights reserved
ii
ISO/DISPRF 24835-1:2025(en)
Contents
Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principles . 2
5 Apparatus and materials . 4
5.1 Apparatus . 4
5.2 Materials and tools . 6
6 Sampling and sample preparation . 6
6.1 Sampling . 6
6.2 Sample preparation . 7
7 Composition analysis . 7
7.1 X-ray diffractometer testing . 7
7.2 Data processing . 8
7.3 Reference intensity analysis . 9
7.4 Composition calculation . 9
8 Calculation of shale mineral brittleness index. 9
9 Precision . 9
9.1 Repeatability . 9
9.2 Reproducibility . 9
10 Test report . 10
Annex A (normative) X-ray diffraction data . 11
Annex B (normative) Reference intensity testing and calculation method . 21
Bibliography . 24

iii
ISO/DISPRF 24835-1:2024（2）2025(en)
Foreword
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This document was prepared by Technical Committee ISO/TC 193, Natural gas, Subcommittee SC 3, Upstream
area.
A list of all parts in the ISO 24835 series can be found on the ISO website.
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© ISO/DIS 24835-1:2024(1)– 2025 – All rights reserved
iv
ISO/DISPRF 24835-1:2025(en)
Introduction
This document has been developed to address the need for evaluating shale brittleness in the production of
shale gas. In order to boost shale gas production, , it is essential to create flow paths within shale gas reservoirs
through hydraulic fracturing. The shale brittleness index, serving as a crucial parameter for forecasting the
complexity of hydraulic fracturing cracks, is a vital benchmark for identifying high-quality shale gas reservoirs.
Therefore, a standardized approach for calculating the shale brittleness index can assist stakeholders,
including (e.g. oil companies, oilfield service providers, investment firms and governments, in) to accurately
pinpointingpinpoint "sweet spots" within shale gas reservoirs, selectingselect promising areas with
development potential, and facilitatingfacilitate efficient shale gas development.
In the global shale gas production industry, two types of optimal methods for characterizing shale brittleness
index are preferred: the mineral composition method and the rock mechanics method. these methods are
preferredThis is due to their theoretical effectiveness, operational generality and result reliability. The ISO
24835 series has been developed on the basis of these two methods.
v
ISO/DIS 24835-1:2025(en)
DRAFT International Standard
Natural gas upstream area — Determination and calculation of shale
brittleness index — —
Part 1:
Determination of shale mineral characteristics based on X-ray
diffraction method
1 Scope
This document specifies the principles, instruments, materials, experimental conditions and the sampling and
composition analysis steps required for testing mineral composition using the X-ray diffraction method, as
well as the method and precision requirements for calculating shale brittleness index based on mineral
composition.
This document is applicable to reservoir quality evaluation and sweet spot identification in shale gas
production.
2 Normative references
The following documents are essential to the application of the standard. For dated references, only the edition
cited applies. For undated references, their latest edition of the referenced document (including any
amendments) applies.
ISO 3310--1, Test sieves — Technical requirements and testing — Part 1: Test sieves of metal wire cloth
ISO 5725--2, Accuracy (trueness and precision) of measurement methods and results Part 2: Basic method for
the determination of repeatability and reproducibility of a standard measurement method
ISO 5725--6, Accuracy (trueness and precision) of measurement methods and results — Part 6: Use in practice
of accuracy values
ISO 14532, Natural gas — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions in ISO 14532 and the following apply:
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— — ISO Online browsing platform: available at https://www.iso.org/obp
— — IEC Electropedia: available at https://www.electropedia.org/
3.1 3.1
brittle mineral
mineral that exhibits virtually no plastic deformation prior to fracturing under external forces
ISO/DISPRF 24835-1:2024（2）2025(en)
Note 1 to entry: Brittle minerals are typically found in global shale gas reservoirs, include quartz, plagioclase,
kalifeldspar, calcite, dolomite and pyrite (see References [2 [2]] to [9 [9])]) and can also include ankerite and siderite.
Note 2 to entry: Adapted from ISO 18684:2020, 3.4.
3.2 3.2
shale brittleness index
index derived from a particular brittleness characterization principle and algorithm among various options,
used for comparing the brittleness levels of different shales
3.3 3.3
shale mineral brittleness index
shale brittleness index derived through calculation based on the mineral composition of the shale
4 Principles
Each crystal mineral features a specific X-ray diffraction pattern. The intensity of characteristic peaks is
functionally proportional to the specific mineral content. The reference intensity of single mineral is tested by
means of mixed comparison. Shale mineral brittleness index is calculated from brittle mineral content. The
brittle mineral content is obtained from the X-ray diffraction pattern of shale powder sample and
Formula (1)Formula (1). .
n
𝐼𝐼 𝐼𝐼
𝑖𝑖 𝑖𝑖
𝑋𝑋 = /[� ] (1)
𝑖𝑖
𝐾𝐾 𝐾𝐾
𝑖𝑖 𝑖𝑖
𝑖𝑖=1
where
𝑋𝑋 is the mass percentage content of mineral i, %;
𝑖𝑖
𝐼𝐼 is the integral intensity of the selected diffraction peak of mineral i, counts per second;
𝑖𝑖
𝐾𝐾 is the reference intensity of mineral i, dimensionless;
𝑖𝑖
𝑖𝑖 is a specific mineral in shale, such as quartz and calcite;
n is the total number of mineral categories in shale.
The process for determining and calculating the shale mineral brittleness index is shown in Figure 1Figure 1.
© ISO/DIS 24835-1:2024(1)– 2025 – All rights reserved
ISO/DISPRF 24835-1:2025(en)
Start
Shale sampling
X-ray diffraction sample preparation
X-ray diffraction testing
Identi�ication of shale mineral composition and
their characteristic peak integral intensity
NO
Has the reference
Aluminum oxide powder + quartz and other
intensity data table
mineral standard sample
been established?
X-ray diffraction sample preparation
YES
Typical mineral reference strength
X-raw diffraction testing
data table
Integral intensity of characteristic peaks of
mineral standards such as aluminium oxide and
quartz
Reference intensity of common minerals
Calculation of shale mineral composition
content
Shale mineral brittleness index
End
ISO/DISPRF 24835-1:2024（2）2025(en)

Figure 1 — Flowchart of shale mineral brittleness index determination and calculation
5 Apparatus and materials
5.1 Apparatus
5.1.1 5.1.1 X-ray diffractometer (see Figure 2Figure 2),), which shall meet the following requirements:
a) a) X-ray source shall select CuKα.
© ISO/DIS 24835-1:2024(1)– 2025 – All rights reserved
ISO/DISPRF 24835-1:2025(en)
b) b) Absolute value of current and voltage stability deviation shall not exceed 0,005 %.
c) c) X-ray tube power shall be equal to or higher than 2 kW.
d) d) Monochromator efficiency shall be at least 25 %.
e) e) Resolution of X-ray diffraction receiver shall be better than 0,05°.
f) f) Lower limit of narrow-angle diffraction angle testing range shall be equal to or less than 3°.
Testing range of wide-angle shall cover 5° to 90°.
g) g) For verification of main peak using standard substances (5.2.5(5.2.5), ), 𝜃𝜃 deviation shall
double
be equal to or less than 0,05°.

Key
1 X-ray generator
2 angular instrument
3 sample
4 computer system
5 measurement recording system
6 X-ray diffraction receiver
ISO/DISPRF 24835-1:2024（2）2025(en)
Figure 2 — Schematic diagram of X-ray diffractometer
NOTE 1 Typical X-ray sources include CuKα and CoKα. CuKα is generated by electrons transitioned from L layer to K
layer by high-energy electron stream bombardment on copper as the target. CoKα is generated by electrons transitioned
from L layer to K layer by high-energy electron stream bombardment on cobalt as the target. The selection of X-ray source
is mainly based on the sample properties and the crystal structure to be measured.
NOTE 2, 𝜃𝜃 , also known as 2,2𝜃𝜃, refers to the angle between incoming X-ray beam and the diffraction detector. In
double
an X-ray diffraction device, the ray sent from the X-ray source arrives at the sample with certain angle ().(𝜃𝜃). When
Bragg’s Law is met, X-ray diffraction occurs on the crystal face of sample. The X-ray after diffraction is received by the
detector with an angle ().(𝜃𝜃). Therefore, a double angle ()(𝜃𝜃 ) is formed by the combination of the incoming angle (𝜃𝜃)
double
and the diffraction angle ().(𝜃𝜃).
5.1.2 5.1.2 Grinder, the grinding chamber diameter of which should be higher than 35 mm.
5.1.3 5.1.3 Convection oven, the temperature control accuracy of which should be better than ±2 K.
5.1.4 5.1.4 Electronic balance, which can be read to the nearest 0,001 g.
5.1.5 5.1.5 Drilling machine, which can be equipped with a diamond drill bit of a diameter 10 mm.
5.2 Materials and tools
5.2.1 5.2.1 Agate mortar, which should have a diameter higher than 50 mm.
5.2.2 5.2.2 Sample box, which should have a diameter higher than 50 mm.
5.2.3 5.2.3 Standard sieve, with round perforations of diameter 45 μm, which shall be compliant
withconform to ISO 3310-1 requirements.
5.2.4 5.2.4 Chloroform, analytical purity of which shall be 99 %.
5.2.5 5.2.5 Aluminium oxide powder standard substance, which shall have a purity higher than 99,9.
NOTE 1 Either NIST SRM 640 — Aluminium oxide powder or GBW(E)130592 — Aluminium oxide powder is a suitable
standard substance for the performance of X-ray diffractometer.
5.2.6 5.2.6 Single mineral sample, which shall be well-crystallized quartz, calcite, dolomite, siderite,
feldspar, anhydrite, plagioclase, gypsum, pyrite, siderite, Thenardite, barite, halite, glauberite, laumontite,
analcime, illite, kaolinite and chlorite samples with known accurate contents.
6 Sampling and sample preparation
6.1 Sampling
6.1.1 6.1.1 Obtain a full-hole shale core from downhole. Sampling shall be carried out in accordance with
the sampling rule (see Figure 3Figure 3).). As a vertical sampling rule, designate a certain depth as the first
sampling surface. Then, determine the second sampling surface, which shall be 50 mm below. As a horizontal
sampling rule, mark a sampling line every 120° on the cylindrical surface between the two sampling surfaces.
Samples shall be drilled evenly along the sampling line. Sequentially drill 20 g ± 0,5 g of debris samples from
each line using a drilling machine (5.1.5(5.1.5).). Mix the samples from the three sampling lines evenly and
place them in the sample box (5.2.2(5.2.2).).
6.1.2 6.1.2 Information on the sample source shall be recorded, including well number, sampling point
depth, stratigraphic position and appearance description.
© ISO/DIS 24835-1:2024(1)– 2025 – All rights reserved
ISO/DISPRF 24835-1:2025(en)
Key
1 full-hole core
2 first sampling surface
3 second sampling surface
4 longitudinal sampling interval
5 0° sampling line
6 0° sampling line
7 0° sampling line
Figure 3 — Schematic diagram of sampling rule
6.2 Sample preparation
6.2.1 6.2.1 Chloroform (5.2.4(5.2.4)) shall be used to wash for oil-containing samples.
6.2.2 6.2.2 Place the samples (6.1.1(6.1.1 or 6.2.16.2.1)) into a 331,15 K convection oven (5.1.3(5.1.3).).
The samples shall be dried and weighed every 2 h until the weight change is below 0,01 g.
6.2.3 6.2.3 Grind samples in a grinder (5.1.2(5.1.2).). A standard sieve (5.2.3(5.2.3)) shall be utilized to
sieve the samples, ensuring that the resulting powder samples have a particle size of less than 45 μm.
6.2.4 6.2.4 Three powder samples (6.2.3(6.2.3)) shall be weighed to 0,5 g ± 0,001 g using the electronic
balance (5.1.4(5.1.4).). Subsequently, each sample shall be placed into a sample holder of an X-ray
diffractometer (5.1.1(5.1.1)) and properly compacted to achieve a flat and uniform surface.
7 Composition analysis
7.1 X-ray diffractometer testing
7.1.1 7.1.1 The X-ray diffractometer shall be switched on and warmed up for 30 min in accordance with
the operating instructions.
7.1.2 7.1.2 Place the sample holder (6.2.4(6.2.4)) on the sample rack of the X-ray diffractometer.
ISO/DISPRF 24835-1:2024（2）2025(en)
7.1.3 7.1.3 The 𝜽𝜽 scan speed shall be set to 2°/min and data shall be collected with a step width of
double
0,02°, scan range from 3° to 45°.
7.1.4 7.1.4 Start scanning and record the diffraction intensity at different 𝜽𝜽 angles.
double
7.1.5 7.1.5 Record the diffraction intensity at different 𝜽𝜽 angles.
double
7.1.6 7.1.6 Plot the X-ray diffraction patterns of the samples (6.2.4(6.2.4).).
7.2 Data processing
7.2.1 7.2.1 The X-ray diffraction spectrum baseline shall be determined in accordance with the baseline
determination schematic in Figure 4Figure 4 (a), processing the X-ray diffraction spectrum (7.1.6(7.1.6)) to
produce a background-subtracted diffraction pattern [see Figure 4Figure 4 (b)].

(a)  (b)
Key
Y I (cps)
Figure 4 — Schematic diagram of X-ray diffraction spectrum background subtracting
7.2.2 7.2.2 The identification of the types of minerals contained in the sample (6.2.4(6.2.4)) shall be based
on the background-subtracted diffraction spectrum (7.2.1(7.2.1),), utilizing the typical X-ray diffraction data
for minerals as outlined in Annex AAnnex A.
© ISO/DIS 24835-1:2024(1)– 2025 – All rights reserved
ISO/DISPRF 24835-1:2025(en)
7.2.3 7.2.3 Table B.1B.1 shall be utilized to identify the characteristic diffraction peaks of each mineral
component on the spectrum (7.2.2(7.2.2)) and subsequently, the integral intensity of each characteristic peak
shall be calculated.
7.3 Reference intensity analysis
7.3.1 7.3.1 For the X-ray diffractometer used for mineral composition analysis for the first time, the
reference intensity of the single mineral sample (5.2.6(5.2.6)) shall be determined using the method provided
in Annex BAnnex B.
NOTE The reference intensity test results are used as constants for calculating shale mineral composition using the
specified X-ray diffractometer. For the untested reference intensity of the X-ray diffractometer, Table B.1Table B.1
provides examples of test results as reference. Based on experience, the deviation in calculating shale mineral
composition is greater than that calculated based on measured reference intensity.
7.4 Composition calculation
7.4.1 7.4.1 The shale mineral composition shall be calculated in accordance with
Formula (1)Formula (1).
7.4.2 7.4.2 The same steps from 7.1.17.1.1 to 7.4.17.4.1 in this document shall be followed to complete
testing and mineral composition calculation for the remaining two samples (6.2.4(6.2.4).). Report the average
of the three test results for brittle mineral content.
8 Calculation of shale mineral brittleness index
The shale mineral brittleness index using the measured brittle mineral content results (
...