Before Guyana approves an offshore oil development, operators must first estimate the greenhouse gas (GHG) emissions expected from the project. Those projections form part of the environmental impact assessment (EIA), providing regulators with an early picture of a project’s environmental footprint long before the first barrel of oil is produced.
The estimates provide the EPA with an assessment of the project’s expected greenhouse gas emissions, allowing regulators to evaluate environmental impacts, review proposed mitigation measures, and compare projected emissions with actual performance once production begins.
This has become standard practice for developments in the Stabroek Block, leading up to Longtail.
The estimates draw on planned production activities, equipment specifications, fuel consumption, expected operating hours, and internationally recognized emission factors.
The EIA for ExxonMobil Guyana’s proposed Longtail development illustrates how this process works.
The assessment identifies two main categories of direct GHG emissions. Point sources include diesel combustion from power generation units, drillships, the floating production, storage and offloading (FPSO) vessel, and routine flaring. Area sources include fuel consumed by marine support vessels and helicopters supporting offshore operations.
For example, the Longtail EIA estimates that “total estimated annual direct GHG emissions during drilling and installation are expected to grow from 235 kilotonnes per year in 2027 through 2029 to 2,530 kilotonnes per year in 2030 through 2031”.
To prepare these projections, developers use equipment specifications, vendor information, projected operating conditions, and emission factors published by organizations such as the American Petroleum Institute and the U.S. Environmental Protection Agency.
The emissions estimate, however, is only one part of the process.
The agency considers the wider environmental assessment, including potential impacts on air quality, marine ecosystems, biodiversity, fisheries, nearby communities, and the mitigation measures proposed by the developer before deciding whether to grant environmental authorization.
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Once a project receives approval and production begins, those estimates are used as a starting point for monitoring how the project performs against its original projections.
Operators monitor and report actual greenhouse gas emissions under environmental permit requirements and industry standards. Actual emissions can differ from original projections because of changes in production levels, equipment performance, maintenance activities, or operational events. Where necessary, emissions assessments are updated as projects move through commissioning, start-up, and long-term production.
According to the Longtail EIA, Guyana’s GHG emissions were estimated at approximately 14.96 million tonnes of carbon dioxide equivalent in 2022. While new offshore developments are expected to increase national emissions, the assessment concludes that individual projects represent a relatively small contribution compared with Guyana’s overall carbon sink and only a fraction of regional GHG emissions.
The findings align with the government’s position that petroleum development, even with production above 900,000 barrels per day, can coexist with Guyana’s broader climate strategy.
