Carbon intensity (CI) measures carbon generated per unit of energy. It can be used to compare alternative sources of energy or even various crude oils. The CI of oil and gas production varies widely across global oil plays. Life cycle extraction from some unconventional plays (e.g., tar sands) have very high Cis. North American shale plays have relatively high carbon intensity.

This paper applies peer-reviewed processes across broad averages of shale activity in North America for the Eagle Ford, Permian and Bakken plays. We compare them with Middle East activity. This approach accounts for emissions from exploration, drilling and completions, production, processing, and transportation. The analysis tool is an open-source engineering-based model, developed at Stanford University, called the Oil Production Greenhouse Gas Emissions Estimator (OPGEE). OPGEE makes estimates of emissions by using up to 50 parameters for each modeled field. Data sources include government sources, technical papers, satellite observations, and commercial databases.

OPGEE estimates show the highest values are in areas with extensive flaring of natural gas and for very heavy crude oils. Heavy oils requiring large energy inputs (e.g., steam flooding) and/or the use of light hydrocarbon diluents for transportation have much higher values of carbon intensity. Examples illustrating how OPGEE can be used to evaluate the CI of public policy actions are provided. Further sensitivity analyses to pad drilling and improving well performance are shown, and the CI impacts associated with hydraulic fracturing.

While Middle East crude will remain vital to global supplies, unconventional production, especially from light tight oil (LTO), is the most significant new source of fossil fuels in the last decade. Under almost any conceivable carbon constraints, oil usage will continue for many decades and increase in the near term. Operators, governments and regulators should avoid "locking in" the development of sub-optimal resources and provide incentives for LTO operators to manage resources sustainably. Oil producers must prepare by eliminating development of marginal projects, eliminating flaring, optimizing hydraulic fracture treatments, increasing the use of pad drilling, using improved recovery methods (e.g., enhanced oil recovery using anthropogenic CO2), reducing energy use, and eliminating unnecessary gas waste.

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