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4. Mining Natural Gas

See Climate Change (Stationary Energy and Industrial Processes) Regulations 2009: 15–17

4.1   Overview

The formula for calculating emissions associated with the activity of mining natural gas accounts for greenhouse gas emissions generated during the production, processing and eventual combustion of the natural gas. Any natural gas exported or sold to an opt-in participant may be explicitly deducted from your calculated emissions. Fugitive emissions lost during the distribution and use of natural gas have already been included in the equation and do not need to be reported on separately.

Data must be sourced from direct measurement of the carbon content and other properties of classes of natural gas by gas chromatography and other techniques at the point of sale. As the measured gas properties are used to calculate emissions instead of default emissions factors for CO2, no provision is made for unique emissions factors.

Emissions from venting, flaring and own use of gas during production and processing must be estimated using the hydrocarbon accounting system needed for process control.

4.2   Information you are required to collect

The following information must be collected for natural gas mined in the year:

Information to collect How to collect
For each class of gas sold, including to opt-in participants or exported:
  • tonnes of each class of gas sold domestically during the year
  • terajoules of each class of gas sold during the year
  • mass fraction of carbon (mC)
  • directly measured physical quantities
  • at the point of sale ie, the first fiscal metre downstream of gas processing
  • using gas chromatography for chemical properties according to standards specified in Regulation 16(3)
  • tonnes of each class of gas exported during the year
  • measured at the customs point
  • gas can be exported directly or by a third party
For each class of processing emissions (flaring, venting and own use):
  • tonnes of gas of each class from gas processing
  • terajoules of gas of each class from gas processing
  • may be estimated
  • using the processing facility hydrocarbon accounting system needed for process control
For vented gas, you must also report::
  • mass fraction of carbon dioxide (mCO2) and methane (mCH4)
  • may be estimated
  • using the processing facility hydrocarbon accounting system needed for process control

4.3   Record keeping

The determination of carbon content in mined natural gas can be undertaken using high-precision measurement and analysis equipment which is already in place and used for commercial and technical management reasons.

A hydrocarbon accounting system (HAS) must be used to estimate and report on emissions from flaring, venting and the combustion of natural gas for own use upstream of the sales meter. The HAS is a process model used to manage the gas processing system and not all of the required parameters will be directly measured. The gas miner will need to provide records to show how the values reported were obtained.

Participants must retain sufficient records to enable the Chief Executive of the Ministry of Economic Development to verify the emissions a participant reports in their emissions return. Records must be retained for a period of at least seven years after the end of the year to which they relate.

4.4   Example calculation

Western Cape Pty Ltd is involved in natural gas mining activities at one field in New Zealand. In one year, the company sold 200,000 tonnes of pipeline gas (50,000 of which was to an opt-in participant) and 2675 tonnes of LPG of which 1000 tonnes was exported.

Activity Quantity (tonnes/ year) Quantity (TJ/year) Oxidation factor Mass fraction of carbon Emissions factor for carbon Mass fraction CO2 in vented gas Mass fraction CH4 in vented gas Aggregate CH4 & N2O emission factor Emissions (tCO2-e)
Term used in regulations C D OFGAS mC EFC mCO2 mCH4 EFM+N E
Mined gas – pipeline sales 200,000 9,351 1.0 0.698 3.6641 N/A N/A 0.054 512,013
Mined gas – LPG sales 2675 131.8 0.995 0.82 3.6641 N/A N/A 0.054 8,004
Exports 1000 49.3 0.995 0.82 3.6641 N/A N/A 0.054 2,992
Sold to opt-in 50,000 2338 1.0 0.698 3.6641 N/A N/A 0.054 128,003
Own use 4000 187 0.995 0.698 3.6641 N/A N/A 0.054 10,189
Flaring 600 28 0.980 0.698 3.6641 N/A N/A 0.054 1,505
Venting 1000 N/A N/A N/A N/A 0.12 0.75 N/A 15,870
Total                 416,586

The standard emission equation is E = (OFGAS × mC × EFC × C) + (D × EFM+N)

For sales gas:
Pipeline sales (include to opt in and for export):
(1.0 × 0.698 × 3.6641 × 200,000) + (9351 × 0.054) = 512,013 tCO2-e
LPG sales        (0.995 × 0.820 × 3.6641 × 2675) + (131.8 × 0.054) = 8004 tCO2-e


For processing emissions:
Own use gas       (0.995 × 0.698 × 3.6641 × 4000) + (187 × 0.054) = 10,189 tCO2-e
Flared gas           (0.980 × 0.698 × 3.6641 × 600) + (28 × 0.054) = 1505 tCO2-e
Vented gas (using the equation V = [mCO2 + (21 × mCH4)] × C)
[0.12 + (21 ×0.75)] × 1000 = 15,870 tCO2-e

The total emissions to be reported for the activity of mining natural gas are:
TE = Σ(EFIELD)    = (512,013 + 8004) + 10,189 + 1505 + 15,870 – 2992 – 128,003

= 416,586 tCO2-e

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