In this post I want to share with you how to estimate greenhouse gas emissions in oil and gas industry.
Greenhouse gas (GHG) emissions from oil and gas production activities must be accurately estimated to enhance accountability and formulate efficient mitigation strategies. Particularly, the oil and gas industry is the largest source of methane (CH4) emissions within the energy sector. As the primary component of natural gas, methane is a significantly more potent GHG than carbon dioxide (CO2), trapping up to 25 times more heat in the atmosphere over a standard timeline.
Classification of Greenhouse Gas Emission Sources
Greenhouse gas (GHG) emissions are classified into two main categories: direct emissions, which originate from sources owned or controlled by an organization, and indirect emissions, which result from the organization’s activities but occur at sources owned or controlled by another entity (such as purchased electricity or supply chain logistics).
Direct emission sources are categorized into combustion, process, and fugitive sources. Combustion sources comprise all equipment utilizing fossil fuel combustion, which releases key greenhouse gases such as carbon dioxide (CO2) and methane (CH4). Typical combustion assets include furnaces, heaters, boilers, turbogenerators, flares, incinerators, oxidizers, diesel engines, and burning pits.
Process (or discharge) emissions are released by design through specific equipment configurations, chemical processes, or operational measures. These encompass emissions from processing units, gas transmission discharge systems, and other facility equipment.
Fugitive emissions consist of unintentional releases from piping components, sealed surfaces, and underground pipeline leaks. These typically manifest as low-volume process fluid leaks from seals, packing, and gaskets due to the gradual wear of mechanical joints, seals, and rotating components over time. Specific fugitive sources include valves, connectors, instrument or sampling systems, and seals on pumps, compressors, and agitators. Additionally, fugitive emissions encompass non-point evaporative sources, such as wastewater treatment units, open pits, and surface impoundments.
Indirect emissions occur because of the reporting company’s operations but are generated by sources owned or controlled by another entity. This category primarily includes emissions from the combustion of hydrocarbon fuels used to generate imported or purchased electricity, heating, steam, or cooling.
Calculation of Greenhouse Gas Emissions
One method to estimate greenhouse gas emissions is using API Compendium Methodology. This method is basically from field measurement data by analyse the fuel composition, emitted gas composition, and flow measurement of fuel consumption. Based on this method, the formula used to estimate greenhouse gas emissions are below.
Direct Source – Gas Fuel Combustion Emissions
ECO2 = FC × MWgas × wt% C × (MW CO2/MW C) / 23.685
Where:
ECO2 = emission from CO2 (kg per year)
FC = volume of fuel consumed
MWgas = molecular weight of fuel gas
Wt% C = weight % of atom carbon in gas fuel
MW C = molecular weight of carbon
Direct Source – Emission from Flares
Where:
EF,CO2 = CO2 emission from flare (Gg/year)
QF = annual amount of flow to flare (Sm3)
xi = molar fraction of hydrocarbon compound (i) in the flow sent to flares (fraction of 1)
CNi = some carbons in hydrocarbon composition (i)
FE = flare efficiency (fraction of 1)
XCO2 = molar fraction of CO2 in the flow sent to flare (fraction of 1)
Indirect Source – Emission due to Electricity Imports from National Electricity Network
Where:
EI,CO2 = indirect CO2 emissions from electricity imports from national grid (Gg CO2/year)
Ei,grid = annual amount of electricity received from national grid (MWh)
EF,GE,CO2 = CO2 emission factor for national grid electricity (tonCO2/MWh)
TDL = Power transmission and distribution losses
References:
- Eslamidoost, Z., Arabzadeh, M., Oskoie, V. and Dehghani, S., 2022. Carbon footprint calculation in one of the largest Gas Refinery Companies in the Middle East. Environmental Science and Pollution Research, 29, pp.81609–81623
- Pinem, S., Karuniasa, M. and Abdini, C., 2020. Estimating GHG emission level from oil and gas offshore production facility. In E3S Web of Conferences (Vol. 202, p. 09004). EDP Sciences.