Introduction

Natural gas analysis for hydrocarbons and hydrogen sulfide (H₂S) is required to avoid natural gas and oil escaping from the hole and is part of the ship's standard drilling safety plan.
The absolute quantity of hydrocarbons is the primary safety risk during shipboard operations. Gas monitoring via gas chromatography is a means of quantifying the hydrocarbon risk. H₂S is another significant risk factor for individuals working in the area. Emergency monitors on the drill floor provide early detection of H₂S, while later quantification is performed on the natural gas analyzer (NGA). A primary method of monitoring safety conditions is the concentration ratio of methane to ethane versus temperature (Figure 1). 

Image Added

Figure 1. Risk Assessment for Drilling Safety (IODP).

Hydrocarbon Generation

Hydrocarbon generation in sediments is a result of thermal decomposition (maturation) of biogenic organic matter. C₁–C₄ hydrocarbons may be generated in significant quantities in sediment via two processes:

• Biogenic: biogenic hydrocarbons, typically characterized by methane, are produced in a sulfate-free environment via the reduction of dissolved bicarbonate.
• Thermogenic: thermogenic hydrocarbons are produced in sediments in direct proportion to temperature. C₅ and other heavier hydrocarbons are almost always the result of thermal generation of hydrogen-rich organic matter at temperatures typically ~100°C or greater.

The evolution of sedimentary biogenic organic matter under increasing burial depth and consequent temperature rise is divided into three stages:

• Diagenesis
  • biological, physical, and chemical alteration of sedimentary organic matter that occurs at low temperature (<50°C) in relatively recently deposited sediments (Peters et al., 2005).
• Catagenesis
  • principal zone of oil formation, refers to a temperature range of 50°C~150°C. Liquid and gaseous hydrocarbons together with organic compounds with heteroatoms (oxygen, sulfur, and nitrogen) are released from the kerogen (Figure 2), so the catagenesis stage is called the "oil window."
• Metagenesis
  • Dry gases (mainly methane) are derived from liquid hydrocarbon accumulation in the crust (Figure 3)

GC3-Natural Gas Analysis User Guide: Drilling Safety Monitoring

Manual Information

Author(s):

C. Bennight

Reviewer(s):

L. Brandt, C. Neal, K. Marsaglia

Editor(s):

K. Graber, L. Peters

Management Approval (Name, Title, Date):

D.J. Houpt, Supervisor of Analytical Systems, 9/24/2010

Audience:

Scientists, Laboratory Technicians

Origination date:

5/12/2008

Current version:

Version 1.0 9/24/2010

Revised:

Domain:

Chemistry

System:

Gas Chromatography

Keywords:

Hydrocarbons, Natural Gas, Headspace

Changes to User Guide

Summarize requested modifications to this user guide in an e-mail and/or annotate the PDF file and e-mail change requests to techdoc@iodp.tamu.edu.

User Guide Contents

Topic

See page…

Introduction

Apparatus, Reagents, & Materials

Instrument Calibration/Calibration Verification

Sample Preparation & Analysis

Quality Assurance/Quality Control

LIMS Integration

Health, Safety, & Environment

Maintenance & Troubleshooting (HP6890GC)

Introduction

Overview

Natural gas analysis for hydrocarbons and hydrogen sulfide (H₂S) is required to avoid natural gas and oil escaping from the hole and is part of the ship's standard drilling safety plan.
The absolute quantity of hydrocarbons is the primary safety risk during shipboard operations. Gas monitoring via gas chromatography is a means of quantifying the hydrocarbon risk. H₂S is another significant risk factor for individuals working in the area. Emergency monitors on the drill floor provide early detection of H₂S, while later quantification is performed on the natural gas analyzer (NGA).

Hydrocarbon Gases

• • . C₁–C₄ hydrocarbons may be generated in significant quantities in sediment via

• • biogenic and thermogenic processes.

Image Added
Figure 2. Hydrocarbon Formation Pathways in Geological Situations (Rullkotter, 1993).
Image Added
Figure 3. Hydrocarbon Generation Resulting from Burial of Organic Matter during Geologic Time.

Hydrogen Sulfide

Sulfate-reducing bacteria produce hydrogen sulfide in euxinic sediments. This may occur in a relatively shallow part of the sediment. Thermochemical sulfate reduction of sulfate by hydrocarbons in reservoirs occurs under high temperature (>127°C ~ 140°C).

Theory of Method

Two instruments monitor gases in core headspace and core void samples:

Instruments

The NGA systems are both based on an Agilent 7890 GCs. These systems were further customized with specialized gas injection inlets and various column, detector, and valving systems for gas monitoring

Gases

The GC requires that hydrogen and air are connected to the marked fittings on the back of the instrument. The type of makeup gas must be identified in the method file.

• Air, compressed (Zero-Air +): >50 psi
• Helium, compressed (99.9995% +): >50 psi
• Hydrogen, compressed (99.9995% +): >50 psi

Method

Theory of method

The NGA gas chromatograph is equipped with 2 detectors:

• Flame ionization detector (FID)
• Thermal conductivity detector (TCD)

The TCD flow path travels through a 6 ft x 2.0 mm ID stainless steel (SS) column packed with Poropak T (50/80 mesh), a 3 ft x 2.0 mm ID SS column packed with molecular sieve 13x (60/80 mesh), and 6 ft x 2.0 mm ID SS column packed with 80/100 mesh HayeSep R (acid washed).
The FID flow path traverses a 60 m x 0.25 mm ID capillary column with 0.25 µm DB-1 film.

This instrument measures C₁–C₇ hydrocarbons as well as some additional compounds:

• Methane (CH₄)
• Ethene (C₂H₄)
• Ethane (C₂H₆)
• Propene (C₃H₆)
• Popane (C₃H₈)
• n-Butane (C₄H₁₀)
• iso-Butane (CH₃-C₃H₇)
• n-Pentane (C₅H₁₂)
• iso-Pentane (CH₃-
• GC3: Agilent 6890 gas chromatograph (GC) with flame ionization detector (FID). This instrument measures C₁–C₃ hydrocarbons:
• Methane (CH₄)
• Ethene (C₂H₄)
• Ethane (C₂H₆)
• Propene (C₃H₆)
• Propane (C₃H₈)
• NGA: Agilent 6890 GC with FID and thermal conductivity detector (TCD). This instrument measures C₁–C₇ hydrocarbons as well as some additional compounds:
• Methane (CH₄)
• Ethene (C₂H₄)
• Ethane (C₂H₆)
• Propene (C₃H₆)
• Popane (C₃H₈)
• n-Butane (C₄H₁₀)
• iso-Butane (CH₃-C₃H₇)
• n-Pentane (C₅H₁₂)
• iso-Pentane (CH₃-C₄H₉)
• n-Hexane (C₆H₁₄)
• iso-Hexane (CH₃-C₅H₁₁)
• n-Heptane (C₇H₁₆)
• iso-Heptane (CH₃-C₆H₁₃)
• Nitrogen (N₂)
• Oxygen (O₂)
• Carbon dioxide (CO₂)

The FID column on the NGA cannot separately quantify ethene/ethane and propene/propane, and they are reported as combined values. The TCD column does separate these components.

Instruments

The GC3 and NGA systems are both based on an Agilent 6890 GCs. These systems were further customized with specialized gas injection inlets and various column, detector, and valving systems for gas monitoring.

GC 3

The GC3 system is equipped with a 1/6 inch VALCO union injector with 2 µm screen and an electronically switched 10 port VALCO valve. The column is an 80/100 mesh, 8 ft HayeSep "R" packed column (2.0 mm ID x 1/8 inch OD).
The detector is an FID.

NGA

The NGA gas chromatograph is equipped with 2 detectors:

• Flame ionization detector (FID)
• Thermal conductivity detector (TCD)

NGA Sample Flow Schematics

Standby Mode

He gas flow for standby mode (green lines).

• Line 1: Aux-3—V1-4—V2-5—V2-3—capillary column—V2-4—V2-1—FID
• Line 2: Aux-4—sample inlet—V1-2—V1-3—V1-6—V1-1—V3-3—V3-4—V3-1—V4-3—V4-2—V4-5—V4-4—Vent
• Line 3: Front inlet—V3-5—V3-6—HaySep R column—V3-8—V3-7—V4-9—V4-8—TCD
• Line 4: Back inlet—V4-6—V4-7—MolSieve column—V4-1—V4-10—Vent

Image Added
Figure 9. NGA in Standby Mode.

Injection mode

He carrier gas (green line) and sample gas (red line) flows in the NGA in injection mode. Sample gas fills the sample loops connected to V1 (25 µL), V3 (1 cm³), and V4 (0.5 cm³). He flushes the separation columns.
He gas flow (green):

• Line 1: Aux-3—V1-4—V1-5—V2-3—V2-2—capillary column—V2-4—V2-1—FID
• Line 3: Front inlet—V3-5—V3-6—HaySep R column—V3-8—V3-7—V4-9—V4-8—TCD
• Line 4: Back inlet—V4-6—V4-7—MolSieve column—V4-1—V4-10—Vent

Sample gas flow (purge; red):

• Sample inlet—V1-2—V1-3—V1-6—V1-1—V3-3—V3-4—V3-1—V3-2—V4-3—V4-2—V4-5—V4-4—Vent

Image Added
Figure 10. NGA in Injection Mode.

Run Mode at 0.01 min (open Valve V4)

He (green) and sample gas (red) flows in the NGA 0.01 min after start of run. Sample gas remains in the sample loop connected to V1 (25 µL) and V3 (1 cm³). After V4 opens, He returning from the back inlet pushes the sample gas out of the sample loop and into the molecular sieve column. Separated elements are detected by TCD.
He gas flow:

• Line 1: Aux-3—V1-4—V1-5—V2-3—V2-2—capillary column—V2-4—V2-1—FID
• Line 2: Aux-4—V1-2
• Line 3: Front inlet—V3-5—V3-6—HayeSep R column—V3-8—V3-7—V4-9—V4-10—Vent
• Line 4: Back inlet—V4-6—V4-5

Sample gas flow (purge):

• V1-2—V1-3—V1-6—V1-1—V3-3—V3-4—V3-1—V3-2—V4-3—V4-4—out

Sample gas flow with He:

• V4-5—V4-2—V4-1—MolSieve column—V4-7—V4-8—TCD

Image Added
Figure 11. NGA in Run Mode: 0.01 min after starting run.

Run Mode at 0.07 min (open Valves V1 and V2)

He (green) and sample gas (red) flows in the NGA 0.07–1.79 min after start of run. Sample gas remains in the sample loop connected to V3 (1 cm³). After V1 and V2 open, He from Aux-3 pushes the sample gas out of the sample loop connected to V1 (25 µL) and into the capillary column (60 m) through V2, where it passes into the FID.
He gas flow:

• Line 1: Aux-3—V1-4
• Line 2: Aux-4—V1-2
• Line 3: Front inlet—V3-5—V3-6—HaySep R column—V3-8—V3-7—V4-9—V4-10—vent
• Line 4: Back inlet—V4-6—V4-5—V4-2—V4-1—MolSieve column—V4-7—V4-8

Sample gas flow (purge):

• V3-4—V3-1—V3-2—V4-3—V4-4—out

Sample gas flow with He:

• V4-8—TCD
• V1-3—V1-6—V1-5—V2-3—V2-4—capillary column—V2-2—V2-1—FID
• V1-1—V3-3

Image Added
Figure 12. NGA in Run Mode: 0.07–1.79 min after starting run.

Run Mode at 1.80 min (open Valve V3)

He (green) and sample gas (red) flows in the NGA 1.80–1.82 min after start of run. After V3 opens, He from the front inlet pushes the sample gas out of the 1 cm³ sample loop into the HaySep column.
He gas flow:

• Line 1: Aux-3—V1-4—V1-3—V1-6—V1-5—V2-3—V2-4
• Line 2: Aux-4—V1-2—V1-1—V3-3—V3-2—V4-3—V4-4—out
• Line 3: Front inlet—V3-5—V3-4
• Line 4: Back inlet—V4-6—V4-5—V4-2—V4-1—MolSieve column—V4-7—V4-8—TCD

Sample gas flow with He:

• Capillary column—V2-2—V2-1—FID
• B3-4—V3-1—V3-8—HaySep R column—V3-6—V3-7

Image Added
Figure 13. NGA in Run Mode: 1.80–1.82 min after starting run.

Run Mode at 1.83 min (close Valve V4)

He (green) and sample gas (red) flows in the NGA 1.83–8.49 min after start of run. After V4 closes, He from the back inlet flushes the molecular sieve column (backflush). Gas samples separated by the HaySep column enter the TCD through V4.
Helium gas flow:

• Line 1: Aux-3—V1-4—V1-3—V1-6—V1-5—V2-3—V2-4—capillary column—V2-2—V2-1—FID
• Line 2: Aux-4—V1-2—V1-1—V3-3—V3-2—V4-3—V4-2—V4-5—V4-4—out
• Line 3: Front inlet—V3-5—V3-4—V3-1—V3-8

Sample gas flow with He:

• HaySep R column—V3-6—V3-7—V4-9—V4-8—TCD

Backflush:

• Line 4: Back inlet—V4-6—V4-7—MolSieve column—V4-1—V4-10—vent

Image Added
Figure 14. NGA in Run Mode: 1.83–8.49 min after starting run.

Run Mode at 8.50 min (close Valve V3)

He gas (green) and sample gas (red) flows in the NGA 8.50–9.09 min after start of run. After V3 closes, He from the front inlet flushes the HaySep column and the line leading to the TCD (backflush).
He gas flow:

• Line 1: Aux-3—V1-4—V1-3—V1-6—V1-5—V2-3—V2-4—capillary column—V2-2—V2-1—FID
• Line 2: Aux-4—V1-2—V1-1—V3-3—V3-4—V3-1—V3-2—V4-3—V4-2—V4-5—V4-4—out
• Line 3: Back inlet—V4-6—V4-7—MolSieve column—V4-1—V4-10—vent

Backflush:

• Line 3: Front inlet—V3-5—V3-6—HaySep R column—V3-8—V3-7—V4-9—V4-8—TCD

Image Added
Figure 15. NGA in Run Mode: 8.50–9.09 min after starting run.

Run Mode at 10.0 min (close Valves V1 and V2)

He (green) and sample gas (red) flows in the NGA 9.09–10.0 min after start of run. After V1 and V2 close, He flow returns to standby mode.
He gas flow:

• Line 1: Aux-3—V1-4—V1-5—V2-3—V2-2—capillary column—V2-4—V2-1—FID
• Line 2: Aux-4—V1-2—V1-3—V1-6—V1-1—V3-3—V3-4—V3-1—V3-2—V4-3—V4-2—V4-5—V4-4—out
• Line 3: Front inlet—V3-5—V3-6—HaySep R column—V3-8—V3-7—V4-9—V4-8—TCD
• Line 4: Back inlet—V4-6—V4-7—MolSieve column—V4-1—V4-10—vent

Image Added
Figure 16. NGA in Run Mode: 9.09–10.0 min after starting run.

NGA Startup

The chromatography application ChemStation controls GC data acquisition and processing. It can be run either online or offline. Offline mode can be run without communication with the GCs, so it is useful for reintegrating or reprocessing chromatograms. Online mode requires communication with the GC.

• Turn on the GC. WARNING: Before turning on the GC, make sure the gas lines are open.
  The 6890 GC performs a comprehensive self-evaluation and shows real-time diagnostics on the screen. Warning, Fault, or Bad Main Board & Fatal Error messages require troubleshooting before moving to the next step (see Maintenance & Troubleshooting (HP6890GC)).
• Click the Agilent Control Panel, then select NGA1 or NGA2, then Launch to start ChemStation. The Method and Run Control window opens. At startup, ChemStation uses the method last used (shown on the main screen). In addition, the GC LCD shows the loaded settings from ChemStation. Settings changed on the GC using the GC control panel are also made to ChemStation, and parameter changes entered into ChemStation are made to the GC. ChemStation will prompt to save changes.

• To load a different method in Chemstation:

  • Click Method > Load Method, select the method from the list, and press OK or
  • Click the Method tab on the left side of the window and select a method to load
• The system automatically loads the new method selected in ChemStation to the appropriate GC. Oven and detector temperatures may increase immediately after a new method is loaded, and the FID will ignite when the detector temperature reaches 150°C. Sometimes, the GC beeps because the FID flame is out, especially after a long idle period. See Maintenance & Troubleshooting (HP6890GC).
• If the GC has been turned off for longer than a week, then bake the column for 8 hr with gas flowing (manually set the oven temperature to 175°C for GC3 or 275°C for NGA).

Instrument Operation

Before unknown samples can be analyzed for headspace gases, each GC system must have a valid calibration curve and the calibration curve must have been verified using a calibration verification standard.

Creating a Calibration Curve

Running a Calibration Verification Standard

Running a Blank

Running a Gas Sample

Sample Preparation 

There are two primary sample types used for natural gas analysis.

• Headspace gas, which is obtained from core samples by heating a sample to ~70°C.

• Void gas collected with a vacuum vial.

Occasionally, cores that come on deck have voids with large amounts of free gas. Free gas must be sampled using a sampling device that penetrates the liner and provides a channel for the gas to be drawn into a gas-tight syringe, vacuum vial, or gas sampling bag.

Headspace Gas

Collect samples from a freshly cut core section at a position within 0.5 inch of the inner side of the core liner (where sample has not been disturbed by contact with drilling fluid or core liner). In addition, the sample must be taken prior to the use of acetone or any other organic solvent in the catwalk area.
The curator authorizes the sampling plan before coring; therefore, the chemistry specialist must know the catwalk sampling plan before taking samples.

Collecting a Void Gas Sample

Data Upload

Data is uploaded from the NGA via a multi-step process:

1. When the run is complete, a macro (NGA_MUT.MAC) is automatically called, as configured in the method file. The macro copies information from the method directory to C:\LIMS\NGA\data
2. An in-house program called MegaUploadaTron (MUT) monitors the data folder locations and when a file is copied in initiates the next steps of the upload process.

• The file is opened and read, and data points are uploaded to LIMS
• The data files are compressed (zipped) and uploaded as well
• LIMS analysis codes are NGAFID, and NGATCD

1. After the upload to LIMS is complete, MUT moves the data files to an archive directory at C:\DATA\GC3\archive or C:\DATA\NGA\archive.
2. If an upload error occurs, the files are not archived and MUT will report the error in the main window (only).

Quality Assurance/Quality Control

QA/QC for GC3/NGA analysis consists of instrument calibration and continuing calibration verification using check standards, instrument blanks, and replicate samples.

Analytical Batch

An analytical batch is a method-defined number of samples with which QC samples including calibration verification, blank, and replicate samples are run. Samples are implicitly grouped into batches based on the spacing between CV samples.

QC Samples

Blank

• The blank determines the level of contamination originating from the laboratory environment (air) and sample path in the GC (injection port with screen, sample loop, and separation column).
• Run a blank with each batch of samples by injecting 5 mL of ambient laboratory air into the GC using the same syringe used to inject headspace gas samples.
• All calibrated values other than O₂ and N₂ should be nondetectable in the blank. If aberrant peaks appear, bake the column for 8 hr and repeat the blank analysis.

Calibration Sample

• Five to seven levels of calibration samples (standard gases) are used to create a calibration curve, which is saved with the measurement data (see Instrument Calibration/Calibration Verification).
• Correlation coefficient values for calibration curves should be 0.99 or better, except O₂ and N₂, which should be 0.95 or better.

Calibration Verification (CV) Sample

• Select one of the 5–7 calibration samples from the calibration curve for the calibration verification sample.
• Run a CV sample at least every shift that samples are taken (see Instrument Calibration/Calibration Verification).
• The CV should fall within 3% of the calibrated value; O₂ and N₂ should be within 10% of the calibrated value.

Control Limits

For a system to be considered in control, all QA/QC samples (blank and calibration verification) must be in control.

In Control

A QA/QC sample is in control when the sample analysis result is within a certain tolerance of acceptable limits (see above). Calibration verification samples should be within acceptable limits of the actual value calculated against the calibration curve (see Calibration Verification (CV) Sample) and blanks should be within acceptable limits of background levels of headspace hydrocarbons and gases (see Blank). When the system is in control, as indicated by acceptable results on QA/QC samples, analytical results for unknown samples are considered to be reliable.

Out of Control

If the control limits are exceeded, the instrument system is considered out of control and all samples in the current analytical batch are invalid and must be rerun after the system is proved to be in control.

LIMS Integration

LIMS Components

Health, Safety & Environment

Safety

• The following parts are dangerously hot. Avoid touching these areas and cool completely to room temperature before servicing them:
• Inlets
• Oven
• Detectors
• Column nuts
• Be careful when working behind the instrument; during cooldown cycle the oven emits hot exhaust that can cause burns.
• Do not place temperature-sensitive items (e.g., gas cylinders, chemicals, regulators, and plastic tubing) in the path of the heated exhaust.
• Insulation around inlets, detectors, and valve box contains refractory ceramic fibers. Avoid inhaling particles and wear personal protective equipment including gloves, safety glasses, and dust/mist respirator when working in these areas.
• Do not leave flammable gas flows on if GC will be unmonitored for long periods of time (however, leave carrier gas on for column flow).
• Always operate the instrument with the cover properly installed.

Maintenance & Troubleshooting (HP6890GC)

Use the Status and Info keys on the GC keypad as a first check when something goes wrong.

Troubleshooting

Faults

• Beeping instrument (cancel beep by pressing Clear on the instrument keyboard)
• One beep: instrument fault, warning, or shutdown
• Series of beeps: gas flow cannot reach setpoint and flow will be shut down after 1–2 min
• Continuous beep: thermal shutdown
• Blinking setpoint on GC display
• Control table setpoint blinking: gas flow, valve, or oven shutdown
• Detector On/Off line blinking: pneumatics or detector failure
• Instrument screen messages (press Clear to remove message)
• Caution: configuration problems
• Error: setpoint out of range or incorrect hardware
• Popup: shutdown, fault, or warning (see error table)
• FID will not stay lit
• Make sure the dessicant in the hydrogen generator is not saturated with water (replace/recharge as necessary).
• Check water level in hydrogen generator

Leak Checking

When checking for leaks, check both parts of the system:

• External leaks: gas cylinders, gas purifiers/traps, regulator fittings, supply shutoff valves, GC supply fittings.
• GC leaks: inlets, purge vents; column connections to inlets, detectors, valves, splitters, adapters, and unions.

For safe leak-checking and flow measurement:

• Purge flowmeters with inert gas after measuring a flammable gas (such as hydrogen).
• Measure gases individually.
• Turn off detectors while measuring gas flows.

Column Size and Carrier Gas Flow Rate

LIMS Component Tables

The following tables represent all of the LIMS components for the following analysis codes:

• NGAFID - C1-C7 hydrocarbons by flame ionization detector
• NGATCD - C1-C3 hydrocarbons and fixed gases by thermal conductivity detector
• GC3 (legacy) - C1-C3 hydrocarbons by flame ionization detector; this system is no longer aboard, but at the time was faster than the previous version of the NGA; the Agilent 7890 NGA GCs are fast enough to make the separate GC3 unnecessary

Archive Version

NGA User Guide: 29th September 2022

Instrument Calibration/Calibration Verification

Overview

Before unknown samples can be analyzed for headspace gases, each GC system must have a valid calibration curve and the calibration curve must have been verified using a calibration verification standard.

1

Create/refresh calibration curve (start at least 1 day before reaching site) (see Creating a Calibration Curve).

2

Verify calibration (Running a Calibration Verification Standard).

3

Perform a work flow test (Running a Gas Sample).

Creating a Calibration Curve

1

Prepare 5–7 registered standard gases.

2

Activate GC3/NGA LIMS uploader located at Start > Program Files > IODP > MegaUploadaTron. The uploader must be activated before the calibration is run.

3

In the ChemStation Main menu, click Run Control > Sample Info.

4

Fill in the specific fields on the screen as follows:

• Operator name: LIMS user account (your last name)
• Sample name: name of the standard (e.g., STD_D) and the replicate number (STD_D-1, STD_D-2, etc.)
• Comment: text ID of the standard (scan the label)
  Click OK to close screen.

5

Slowly inject 5000 µL of the first standard gas and observe the floating ball in the flow meter move upward.
Keep the outflow rate on the flow meter <80 mL/min.

6

When the ball in the flow meter indicates flow has fallen to just above 0 (is about to hit 0), press the Start button on the control panel of the GC.

7

When the run has finished, open the Data Analysis screen in ChemStation and click Calibration.

8

On the Main ChemStation menu, select Calibration > Recalibrate.

9

On the Recalibration screen, select Level # and Replace (or Average) as applicable for that level.

10

Repeat Steps 5–9 for 3 replicate standards (CH₄: A 25%, B = 50%, C 75%, D = 99%).

11

Click OK to change the calibration value. For NGA calibration, the same standard can be applied to both the appropriate TCD and FID level; you do not need separate standards for TCD and FID.

Running a Calibration Verification Standard

1

Ensure the uploader is activated and the CV standard is registered in LIMS.

2

Click Run Control in the main menu of ChemStation and select Sample Info.

3

Fill in the specific section on the window as follows:

• Operator name: LIMS user account (your last name)
• Sample name: common name for standard (e.g., STD_D-1)
• Comment: text ID of the standard (scan the label)
  Click OK to close the sample info screen.

4

Prepare the CV standard at approximately the mid-point concentration of the curve.

5

Slowly inject 5000 µL of the standard gas, keeping the outflow rate <80 mL/min.

6

Press Start on the GC control panel when the flow meter is just above 0.

7

When the run is finished, the report will automatically display the values. Click Upload in the uploader to submit the data to LIMS.

Running a Blank

1

To run a blank, in the Main menu click RunControl > Sample Info.

2

Fill in the following fields:

• Operator name: your last name
• Sample name: "BLANK"
• Comment: text ID of the blank (scan the label)
  Click OK to close window and save information.

3

Prepare laboratory air (5000 µL) and inject it into the GC in the same fashion as the standards above when the ChemStation software shows Ready.

4

Press the Start button on the GC control panel to start the run.

5

Confirm the chromatogram on the screen shows no peaks. If peaks are present, the system contamination must be found (injector, detector, sample loop, etc.).

Running a Gas Sample

1

Ensure the uploader has been activated.

2

Click Run Control in the main menu of ChemStation and select Sample Info.

3

Fill in the specific section on the window as follows:

• Operator name: LIMS user account (your last name)
• Sample name: Exp/site/hole/core/coretype/section/interval (e.g., 324-U1351A 5H4 32-35)
• Comment: text ID of sample (scan label)
  Click OK to close sample info screen.

4

Prepare a headspace or void gas sample.

5

Slowly inject 5000 µL of the gas sample, keeping the maximum gas outflow <80 mL/min.

6

Press Start on the GC control panel when the ball on the flow meter is just above 0.

Sample Preparation & Analysis

Overview

There are two primary sample types used for natural gas analysis.

• Headspace gas, which is obtained from core samples by heating a sample to ~70°C.
• Void gas collected with a vacuum vial.

Occasionally, cores that come on deck have voids with large amounts of free gas. Free gas must be sampled using a sampling device that penetrates the liner and provides a channel for the gas to be drawn into a gas-tight syringe, vacuum vial, or gas sampling bag.

Sampling Tools

• Sample coring tool (metal cylinder)
• Sample coring plunger
• Puncture tool (to penetrate plastic liner)
• Headspace vial
• Headspace gasket with crimp top
• Crimping tool
• Permanent marker for labeling

Sampling Procedure and Gas Sample Preparation

Headspace Gas

Collect samples from a freshly cut core section at a position within 0.5 inch of the inner side of the core liner (where sample has not been disturbed by contact with drilling fluid or core liner). In addition, the sample must be taken prior to the use of acetone or any other organic solvent in the catwalk area.
The curator authorizes the sampling plan before coring; therefore, the chemistry specialist must know the catwalk sampling plan before taking samples.

Collecting a Headspace Gas Sample

1

Locate a freshly sectioned core (consult with the curator).

2

Gently push the sample coring tool into the core section slightly inward of the edge.

3

Gently pull out the tool. If the sample recovery (% of coring tool with sample) is >80% (~5–7 cm³), proceed; otherwise repeat Steps 1 and 2.

4

Place the open end of the sample coring tool over a clean headspace gas vial and use the plunger to push the sediment into the vial.

5

Immediately place a gasket with a crimp top over the vial and crimp shut.

6

After sealing the vial, immediately write down the sampling interval, location, and any other information for the sample that was just taken. Generate a proper label and apply it to the vial as soon as possible.

7

Place the vial with the sample in a 70°C oven for 30 min to degas the sediment (use timer).

8

Inject extracted gas sample into the GC using syringe (see
Running a Sample).

Collecting a Void Gas Sample

1

Use the puncture tool to make a hole in the core liner to make a channel for the gas.

2

Quickly collect a free gas sample from the small hole with a syringe.

3

Immediately introduce the gas sample into the GC instruments in the same manner as the headspace samples.

Running a Sample

1

Start GC and operation system at least 1 day before reaching site (the system should be fully calibrated and ready for analysis) (see Advanced User Guide).

2

Ensure LIMS uploader is running.

3

Inject 5 mL of headspace gas after the sample has heated in the oven for 30 min.

4

Click Upload if the uploader is not in automatic mode.

Quality Assurance/Quality Control

Overview

QA/QC for GC3/NGA analysis consists of instrument calibration and continuing calibration verification using check standards, instrument blanks, and replicate samples.

Analytical Batch

An analytical batch is a method-defined number of samples with which QC samples including calibration verification, blank, and replicate samples are run. Samples are implicitly grouped into batches based on the spacing between CV samples.

QC Samples

Blank

• The blank determines the level of contamination originating from the laboratory environment (air) and sample path in the GC (injection port with screen, sample loop, and separation column).
• Run a blank with each batch of samples by injecting 5 mL of ambient laboratory air into the GC using the same syringe used to inject headspace gas samples.
• All calibrated values other than O₂ and N₂ should be nondetectable in the blank. If aberrant peaks appear, bake the column for 8 hr and repeat the blank analysis.

Calibration Sample

• Five to seven levels of calibration samples (standard gases) are used to create a calibration curve, which is saved with the measurement data (see Instrument Calibration/Calibration Verification).
• Correlation coefficient values for calibration curves should be 0.99 or better, except O₂ and N₂, which should be 0.95 or better.

Calibration Verification (CV) Sample

• Select one of the 5–7 calibration samples from the calibration curve for the calibration verification sample.
• Run a CV sample at least every shift that samples are taken (see Instrument Calibration/Calibration Verification).
• The CV should fall within 3% of the calibrated value; O₂ and N₂ should be within 10% of the calibrated value.

Control Limits

For a system to be considered in control, all QA/QC samples (blank and calibration verification) must be in control.

In Control

A QA/QC sample is in control when the sample analysis result is within a certain tolerance of acceptable limits (see above). Calibration verification samples should be within acceptable limits of the actual value calculated against the calibration curve (see Calibration Verification (CV) Sample) and blanks should be within acceptable limits of background levels of headspace hydrocarbons and gases (see Blank). When the system is in control, as indicated by acceptable results on QA/QC samples, analytical results for unknown samples are considered to be reliable.

Out of Control

If the control limits are exceeded, the instrument system is considered out of control and all samples in the current analytical batch are invalid and must be rerun after the system is proved to be in control.

LIMS Integration

LIMS Components

Analysis

Component

Unit

Description

GC3

dat_asman_id

—

Serial number of chromatographic data file in digital asset management database (ASMAN)

dat_filename

—

File name of chromatographic data file containing measurements

run_test

—

Test number of related calibration or QA/QC test

propene

ppmv

Relative concentration of propene in the sample

propane

ppmv

Relative concentration of propane in the sample

ethene

ppmv

Relative concentration of ethene in the sample

ethane

ppmv

Relative concentration of ethane in the sample

methane

ppmv

Relative concentration of methane in the sample

GC3_QAQC

dat_asman_id

—

Serial number of chromatographic data file in ASMAN

dat_filename

—

File name of chromatographic data file containing measurements

run_test

—

Test number of related calibration or QA/QC test

propene

ppmv

Relative concentration of propene in the sample

propane

ppmv

Relative concentration of propane in the sample

ethene

ppmv

Relative concentration of ethene in the sample

ethane

ppmv

Relative concentration of ethane in the sample

methane

ppmv

Relative concentration of methane in the sample

GC3_QCAL

mtd_asman_id

—

Serial number of chromatographic method in ASMAN

mtd_filename

—

File name of the chromatographic method file containing measurements

ethene_corr2

R²

Ethene calibration coefficient

ethene_intercept

—

Intercept of ethene calibration curve

ethene_slope

—

Slope of ethene calibration curve

ethane_corr2

R²

Ethane calibration coefficient

ethane_intercept

—

Intercept of ethane calibration curve

ethane_slope

—

Slope of ethane calibration curve

propene_corr2

R²

Propene calibration coefficient

propene_intercept

—

Intercept of propene calibration curve

propene_slope

—

Slope of propene calibration curve

propane_corr2

R²

Propane calibration coefficient

propane_intercept

—

Intercept of propane calibration curve

propane_slope

—

Slope of propene calibration curve

methane_corr2

R²

Methane calibration coefficient

methane_intercept

—

Intercept of methane calibration curve

methane_slope

—

Slope of methane calibration curve

NGAFID

dat_asman_id

—

Serial number of chromatographic data file in ASMAN

dat_filename

—

File name of chromatographic data file containing measurements

run_test

—

Test number of related calibration or QA/QC test

iso_butane

ppmv

Concentration of iso_butane in a sample

iso_heptane

ppmv

Concentration of iso_heptane in a sample

iso_hexane

ppmv

Concentration of iso_hexane in a sample

iso_pentane

ppmv

Concentration of iso_pentane in a sample

n_butane

ppmv

Concentration of n_butane in a sample

n_heptane

ppmv

Concentration of n_heptane in a sample

n_hexane

ppmv

Concentration of n_hexane in a sample

n_pentane

ppmv

Concentration of n_pentane in a sample

ethane_ethene

ppmv

Concentration of ethane + ethene in a sample

propane_propene

ppmv

Concentration of propane + propene in a sample

methane

ppmv

Concentration of methane in a sample

NGAFID_QA

dat_asman_id

—

Serial number of chromatographic data file in ASMAN

dat_filename

—

File name of chromatographic data file containing measurements

run_test

—

Test number of related calibration or QA/QC test

iso_butane

ppmv

Concentration of iso_butane in a sample

iso_heptane

ppmv

Concentration of iso_heptane in a sample

iso_hexane

ppmv

Concentration of iso_hexane in a sample

iso_pentane

ppmv

Concentration of iso_pentane in a sample

n_butane

ppmv

Concentration of n_butane in a sample

n_heptane

ppmv

Concentration of n_heptane in a sample

n_hexane

ppmv

Concentration of n_hexane in a sample

n_pentane

ppmv

Concentration of n_pentane in a sample

ethane_ethene

ppmv

Concentration of ethane + ethene in a sample

propane_propene

ppmv

Concentration of propane + propene in a sample

methane

ppmv

Concentration of methane in a sample

NGAFID_QC

mtd_asman_id

—

Serial number of chromatographic method in ASMAN

mtd_filename

—

File name of the chromatographic method file containing measurements

iso_butane_corr2

R²

Iso-butane calibration coefficient

iso_butane_intercept

—

Intercept of iso-butane calibration curve

iso_butane_slope

—

Slope of iso-butane calibration curve

iso_heptane_corr2

R²

Iso-heptane calibration coefficient

iso_heptane_intercept

—

Intercept of iso-heptane calibration curve

iso_heptane_slope

—

Slope of iso-heptane calibration curve

iso_hexane_corr2

R²

Iso-hexane calibration coefficient

iso_hexane_intercept

—

Intercept of iso-hexane calibration curve

iso_hexane_slope

—

Slope of iso-hexane calibration curve

iso_pentane_corr2

R²

Iso-pentane calibration coefficient

iso_pentane_intercept

—

Intercept of iso-pentane calibration curve

iso_pentane_slope

—

Slope of iso-pentane calibration curve

n_butane_corr2

R²

n-butane calibration coefficient

n_butane_intercept

—

Intercept of n-butane calibration curve

n_butane_slope

—

Slope of n-butane calibration curve

n_heptane_corr2

R²

n-heptane calibration coefficient

n_heptane_intercept

—

Intercept of n-heptane calibration curve

n_heptane_slope

—

Slope of n-heptane calibration curve

n_hexane_corr2

R²

n-hexane calibration coefficient

n_hexane_intercept

—

Intercept of n-hexane calibration curve

n_hexane_slope

—

Slope of n-hexane calibration curve

n_pentane_corr2

R²

n-pentane calibration coefficient

n_pentane_intercept

—

Intercept of n-pentane calibration curve

n_pentane_slope

—

Slope of n-pentane calibration curve

ethane_ethene_corr2

R²

Ethane + ethene calibration coefficient

ethane_ethene_intercept

—

Intercept of ethane + ethene calibration curve

ethane_ethene_slope

—

Slope of ethane + ethene calibration curve

propane_propene_corr2

R²

Propane + propene calibration coefficient

propane_propene_intercept

—

Intercept of propane + propene calibration curve

propane_propene_slope

—

Slope of propane + propene calibration curve

NGAFID_QC

methane_corr2

R²

Methane calibration coefficient

methane_intercept

—

Intercept of methane calibration curve

methane_slope

—

Slope of methane calibration curve

NGATCD

dat_asman_id

—

Serial number of chromatographic data file in ASMAN

dat_filename

—

File name of chromatographic data file containing measurements

run_test

—

Test number of related calibration or QA/QC test

carbon_dioxide

ppmv

Concentration of carbon dioxide in a sample

ethane

ppmv

Concentration of ethane in a sample

ethene

ppmv

Concentration of ethene in a sample

hydrogen_sulfide

ppmv

Concentration of hydrogen sulfide in a sample

methane

ppmv

Concentration of methane in a sample

nitrogen

ppmv

Concentration of nitrogen in a sample

oxygen

ppmv

Concentration of oxygen in a sample

propane

ppmv

Concentration of propane in a sample

propene

ppmv

Concentration of propene in a sample

Uploading Data to LIMS

Data are uploaded to LIMS automatically using a process explained in the GC3-NGA Advanced User Guide. If the data do not upload to LIMS, contact the laboratory technician.

Health, Safety, & Environment

Safety

• The following parts are dangerously hot. Avoid touching these areas and cool completely to room temperature before servicing them:
• Inlets
• Oven
• Detectors
• Column nuts
• Be careful when working behind the instrument; during cooldown cycle the oven emits hot exhaust that can cause burns.
• Do not place temperature-sensitive items (e.g., gas cylinders, chemicals, regulators, and plastic tubing) in the path of the heated exhaust.
• Insulation around inlets, detectors, and valve box contains refractory ceramic fibers. Avoid inhaling particles and wear personal protective equipment including gloves, safety glasses, and dust/mist respirator when working in these areas.
• Do not leave flammable gas flows on if GC will be unmonitored for long periods of time (however, leave carrier gas on for column flow).
• Always operate the instrument with the cover properly installed.

Maintenance & Troubleshooting (HP6890GC)

Troubleshooting

Faults

• Beeping instrument (cancel beep by pressing Clear on the instrument keyboard)
• One beep: instrument fault, warning, or shutdown
• Series of beeps: gas flow cannot reach setpoint and flow will be shut down after 1–2 min
• Continuous beep: thermal shutdown
• Blinking setpoint on GC display
• Control table setpoint blinking: gas flow, valve, or oven shutdown
• Detector On/Off line blinking: pneumatics or detector failure
• Instrument screen messages (press Clear to remove message)
• Caution: configuration problems
• Error: setpoint out of range or incorrect hardware
• Popup: shutdown, fault, or warning (see error table)
• FID will not stay lit
• Make sure the dessicant in the hydrogen generator is not saturated with water (replace/recharge as necessary).
• Check water level in hydrogen generator

LMUG-GC3-NGAUG2011-230220-1904-144.pdf