Application Note
Energy and Chemicals

Rapid Analysis of Mud Logging Well
Gas Using the Agilent 990 Micro GCAuthor
Jie Zhang
Agilent Technologies, Inc.

Introduction
Mud logging is a process of obtaining information about lithology and fluid content
of a drill area. The monitoring of gas, both types and amount, is one of the mostcritical tasks in mud logging. Accurate gas data recorded during drilling are ofgreat value in proper reservoir evaluation, and may pinpoint potentially overlooked
producing zones. Gas chromatography (GC) is the primarily used technique for gas
identification and measurement during the mud logging process. The most common
component in mud logging well gas is methane; heavier hydrocarbons such asethane (C2), propane (C3), and butane (C4) may indicate an oil or wet gas zone.
Heavier molecules, up to C7, are also required to be monitored.
The analysis speed is important in the mud logging process, because the moredetailed information generated for the unit drilling depth, the more accurate thereservoir evaluation. The Agilent Micro GC is an ideal chromatograph for fast andreliable analysis of well gas. The 990 Micro GC has inherited the characteristics ofthe previous generation1: compactness, energy-friendly, and rapid analysis speed. Inaddition to the listed features, the 990 Micro GC can deliver a better user experience.
The installation of the analytical channel is much easier. It can be done in threesteps within several minutes. A full-color touch screen is used to show the statusof the instrument and key settings such as network setting, available instrument
license, and firmware version. The standard cabinet version can accommodate twoanalytical channels. The extended cabinet version can easily be made by integrating
two standard version mainframes with one main board and one LCD touch screen.
Up to four channels can be accommodated in the extended version. The dynamic
electronic gas control (DEGC) module has been developed to give pressure control
with higher precision, accuracy, and stability.
This study demonstrates the analysis of hydrocarbons in the mud logging process
on the 990 Micro GC platform. A standard version equipped with two analyticalchannels was used for analysis of C1 to C5 hydrocarbons. An extended version,configured with three channels, was used for extended mud logging gas analysis ofheavier components (up to C8).
Tables 1 and 2 show the test conditions
for each channel. Simulated mud logging
well gas was used for configuration
verification. Table 3 lists detailed sampleinformation.

Standard mud logging analysis
Hydrocarbons from C1 to C5 wereanalyzed. The 4 m, CP-PoraPLOT
Q channel (straight DEGC option,no precolumn backflush) was used
for the analysis of propane, butane,isobutane, pentane, and isopentane.
The 10 m, CP-PoraPLOT Q channelwith backflush option was used for theanalysis of C1 and C2. The backflush
option was deployed to flush the heavier
components out from the precolumn
before they entered the analyticalcolumn. This helped reduce the analysis
time, otherwise the analysis would
have lasted longer due to the heavier
components’ late elution on the 10 m
PPQ column.

Extended mud logging analysis
Hydrocarbons as high as C8 wereanalyzed. The 10 m, CP-PoraPLOT Qchannel (backflush DEGC option) wasfor analysis of C1 to C2 hydrocarbons
and CO2; the 4 m, CP-Sil 5CB column
with backflush option was for theanalysis of C3 to C5 hydrocarbons. On
this channel, analytes heavier than C5
were backflushed before they enter
the analytical column, which helped
guarantee a short analysis time and aclean baseline for the next run. The 4m, CP-Sil 5CB channel (straight DEGCoption) was for the analysis of C6 to C82

Instrumentation
Standard Mud Logging

Extended Mud Logging

Components forAnalysis

Channel Type
10 m, CP-PoraPLOT Q, backflush
4 m, CP-PoraPLOT Q, straight

C1, C2, and CO2
C3 to C5

Components forAnalysis

Channel Type
10 m, CP-PoraPLOT Q, backflush

C1, C2, and CO2

4 m CP-Sil 5CB, backflush

C3 to C5

4 m CP-Sil 5CB, straight

C6 to C8

Table 1. Test conditions for standard mug logging well gas analysis.
Channel Type
10 m, CP-PoraPLOT Q, Backflush

4 m, CP-PoraPLOT Q, Straight

Carrier Gas

HeliumHeliumInjector Temperature

110 °C

110 °CInjection Time

40 ms

40 ms

Column Head Pressure

240 kPa

200 kPa

Column Temperature

60 °C

150 °C

Backflush Time

5.5 seconds

NATable 2. Test conditions for extended mug logging well gas analysis.
Channel Type
10 m, CP-PoraPLOT Q,
Backflush

4 m, CP-Sil 5CB,
Backflush

4 m, CP-Sil 5CB,
Straight

Carrier Gas

HeliumHeliumHeliumInjector Temperature

110 °C

110 °C

110 °CInjection Time

40 ms

80 ms

40 ms

Column Head Pressure

240 kPa

150 kPa

200 kPa

Column Temperature

60 °C

60 °C

120 °C

Backflush Time

5.5 seconds

13 seconds

NA

Table 3. Simulated mud logging well gas.
Compound No.

Compound Name

Concentration (mol/mol)

1Methane

2.02%

2Ethane0.251%

3

Propane997 ppm

4Isobutane

495 ppm

5Butane300 ppm

6Isopentane

173 ppm

7Pentane

204 ppm

8Hexane52.6 ppm

9

Methylcyclopentane

50.1 ppm

10Benzene

49.1 ppm

11

Cyclohexane

47.7 ppm

12Heptane49.0 ppm

13

Methylcyclohexane49.2 ppm

14

Toluene49.3 ppm

15Octane

50.4 ppm

16

Nitrogen

Balancehydrocarbons.

Results and discussion
Figure 1 shows the chromatogram forseparation of methane and ethane on the10 m, CP-PoraPLOT Q backflush channel.
There is no CO2 in simulated mug logging
well gas. A natural gas standard withmethane, CO2, and ethane was injected
to find the position of the CO2 peak. The
chromatogram in Figure 1B can be used
as a reference, if the real mud logging
sample contains CO2. Figure 2 shows thechromatogram of C3 to C5 compounds
on the 4 m, CP-PoraPLOT Q channel. In
the mud logging process, separation
speed is a challenge for GC analysis. The
990 Micro GC addresses the separationof the whole sample by analyzing
subsets of sample on different channels.
The stationary phase type, column headpressure, and column temperature are
selected and optimized according to
the specific subset of analytes. This
analysis approach can help accelerate
total analysis speed. The analysis timeis determined by the channel on which
the separation takes the longest time.
In the standard mud logging analysis,
the separation on each channel canbe completed within 30 seconds. The
combination of the analysis results
on different channels gives complete

MethaneEthane

0.1

0.2

0.3

0.4

Figure 1A. Standard mud logging analysis, channel 1: methane and ethane analysis on
10 m, CP‑PoraPLOT Q, backflush.
MethaneCarbon dioxide

Ethane

0.1

0.2

0.3

0.4

RT (min)Figure 1B. Standard mud logging analysis, channel 1: CO2 peak determination by natural gas standard
analysis on 10 m, CP-PoraPLOT Q, backflush.

PropaneIsobutane
ButaneIsopentane

0.11

0.21

0.31

Pentane0.41

RT(min)Figure 2. Standard mud logging analysis, channel 2: C 3 to C5 components analysis on
4 m, CP‑PoraPLOT Q, straight.

3

qualitative and quantitative informationon the entire sample.
Tables 4A and 4B show the retention
time (RT) and area repeatability for
10 injections. The area RSD% is below
0.2% and RT RSD% is in the range of
0.003% to 0.02%, which demonstrates
the excellent performance of the990 Micro GC and guarantees qualitative
Table 4A. Peak area precision of 10 consecutive injections on the 10 m, CP-PoraPLOT Q and
4 m, CP-PoraPLOT Q channels.
CompoundArea(mv × s)

Area RSD%Methane

EthanePropaneIsobutane

ButaneIsopentane

Pentane

8.568

1.585

1.429

0.806

0.512

0.312

0.386

8.567

1.585

1.429

0.806

0.511

0.312

0.386

8.566

1.586

1.429

0.8060.511

0.311

0.386

8.574

1.586

1.429

0.806

0.512

0.313

0.385

8.576

1.588

1.430

0.805

0.511

0.312

0.386

8.576

1.588

1.430

0.806

0.512

0.311

0.386

8.565

1.587

1.429

0.805

0.511

0.311

0.386

8.566

1.585

1.430

0.805

0.511

0.312

0.386

8.581

1.588

1.430

0.805

0.512

0.312

0.386

8.568

1.587

1.430

0.806

0.511

0.312

0.386

0.065

0.080

0.037

0.064

0.101

0.203

0.082

Table 4B. RT and RT repeatability of 10 injections on the 10 m, CP-PoraPLOT Q and 4 m, CP-PoraPLOT Q channels.
MethaneEthanePropaneIsobutane

ButaneIsopentane

PentaneRT (min)Compound

0.224

0.373

0.121

0.176

0.198

0.362

0.407

RT RSD%

0.003

0.004

0.011

0.033

0.006

0.003

0.003

4

and quantitative results with a high levelof confidence.

PropaneFor extended mud logging analysis,channel 1 is same as the standard
version: 10 m, CP-PoraPLOT Q, backflush
for methane, CO2 and ethane analysis.
Figure 3 shows the chromatogram of theC3 to C5 components on channel 2, the4 m, CP-Sil 5CB, backflush channel.
Figure 4 shows the chromatogram ofthe C6 to C8 components on channel 3,the 4 m, CP-Sil 5CB, straight channel.
The last peak, octane, eluted within
35 seconds. Table 5 shows the RT andarea RSD% for the C3 to C8 components
analyzed on the extended mud logging
configuration. The RT RSD% for the C3
to C8 components are better than 0.02%,
and area RSD% are below 1%, which is

Isobutane

ButanePentaneIsopentane

0.1

0.2

0.3
RT (min)0.4

0.5

Figure 3. Extended mud logging analysis, channel 2: C 3 to C5 compounds on 4 m, CP-Sil 5CB, backflush.

Benzene
Methyl-cyclopentane

Cyclohexanen-C7n-C60.15

0.25

Methyl-cyclohexane

0.35
RT (min)Toluene0.45

n-C80.55

Figure 4. Extended mud logging analysis, channel 3: C6 to C8 compounds on 4 m, CP-Sil 5CB, straight.
Table 5. RT and area repeatability for extended mud logging analysis, C 3 to C5
on the 4 m, CP-Sil 5CB backflush channel, and C6 to C8 on the 4 m, CP-Sil 5CB
straight channel.
CompoundRT/min

RT RSD%

Area (mv × s)

Area RSD%

Propane

0.206

0.02

0.446

0.144

Isobutane

0.237

0.018

0.294

0.184

Butane

0.261

0.011

0.162

0.060

Isopentane

0.342

0.007

0.104

0.169

Pentane

0.381

0.008

0.125

0.082

Hexane

0.228

0.004

0.051

0.33

Methylcyclopentane

0.262

0.006

0.077

0.571

Benzene

0.290

0.006

0.065

0.219

Cyclohexane

0.303

0.006

0.068

0.221

Heptane

0.332

0.006

0.074

0.547

Methylcyclohexane

0.392

0.009

0.075

0.290

Toluene

0.450

0.007

0.071

1.024

Octane

0.520

0.008

0.078

0.7685proof of the stable pressure and column
temperature control, and the repeatable
response of the 990 TCD.

Conclusion
This study demonstrates fastanalysis of mud logging well gas
using an Agilent 990 Micro GC. A
two-channel standard configuration
and a three‑channel extended
configuration were used to analyze
C1 to C5 hydrocarbons and C1 to C8hydrocarbons, respectively. The analysis
speed on each channel was optimized
to finish within 35 seconds. The RT

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Printed in the USA, August 7, 20195994-1039EN

and area repeatability were excellent,demonstrating that the 990 Micro GC
is an ideal platform for fast and reliable
mud logging well gas analysis.

Reference
1.

Van Loon, R. Mud Logging –Rapid Analyses of Well Gases
with an Agilent Micro GC,
Agilent Technologies Application
Note, publication number
5991‑2699EN, 2013.