Coproduct Accounting.

In addition to oil, Bakken wells produce water and (associated) gas. Associated gas is used as a fuel for equipment at the well pad, sold as a coproduct, or flared when no infrastructure exists or is insufficient. Therefore, environmental impacts associated with drilling, completion, and production (including flaring) are allocated to both oil and gas.

Upstream GHG emissions and freshwater consumption are allocated to oil and associated gas that is delivered to a gathering pipeline. GHG emissions associated with the flaring of associated gas due to the absence of a pipeline connection are completely allocated to crude because there is no coproduct in this case. However, GHG emissions associated with flaring caused by capacity constraints are allocated to both associated gas and oil. In the base case, 78.4% of the upstream GHG emissions and freshwater consumption are allocated to crude oil, corresponding to the relative amounts of energy of crude oil and associated gas sold. We explore the sensitivity of this allocation in SI Appendix, section 5.3.1 and 5.3.2.

Downstream GHG emissions are allocated to gasoline, jet fuel, ultra-low sulfur diesel, heating fuel oil, bunker fuel/asphalt, petcoke, and surplus H₂ generated via catalytic reforming of naphtha (if any), subject to the limitations of the PRELIM model. The product slate is defined by the refinery configuration and crude characteristics. Light end products are used as refinery fuel gas, representing an upper bound for GHG emissions and a lower bound for resource utilization (e.g., LPG is not part of the product slate, nor are chemical feedstocks such as ethylene).

In plant-level allocation, refinery impacts are allocated to refined products in proportion to their fractions of the energy (or mass) of total refined products. Process-level allocation, by contrast, requires explicit accounting of material through each unit of the refinery. The PRELIM model used for the estimation of refinery impacts accounts for the flows of hydrocarbons through individual refinery process units. Therefore, we were able to investigate the effect of both allocation methods. In our base case, we use process-level allocation.

Environmental impacts for all operations up to and including the refinery are allocated to the aforementioned refined products via energy content.