Lacustrine source rocks and unconventional oil resource plays
A case study from the Eocene Green River Formation of the Uinta Basin, Utah
Abstract
Much information exists on unconventional oil resource plays, their drivers to success and sweet-spot fair- ways. To date, most of the successful oil resource plays are marine Type II kerogen driven systems. Little to no information is available on successful oil resource plays with lacustrine type I kerogen source rocks and in rock as young as Tertiary age. This paper sets out to define the drivers and provide a case study for such plays with the Green River oil resource play of Utah’s Uinta Basin as an example. The Green River petroleum sys- tem of the Uinta Basin has generated vast amounts of hydrocarbons, in the form of gilsonite (~10 billion bar- rels), tar sands (~12 billion barrels), and oil (>700 million barrels) (Johnson, 2016; Schamel, 2015). In addi- tion, the USGS estimates an additional 1.32 trillion barrels of in-place resource in the oil shales of the Green River Formation. Lacustrine source rocks and their type I kerogen follow a different generative path to immis- cible oil generation than the more common marine derived type II kerogens. The oil generative capacity of this lacustrine source is much greater than that of type II kerogen and is characterized by a distinctive highly paraf- finic crude oil. These unique aspects provide exceptionally elevated formation pressures within the source rock in the oil generative window, setting it apart from other unconventional oil resource plays. As in all unconven- tional oil resource plays, identification and mapping of the best source rock is key to defining sweet-spots within the play. With an understanding of source rock distribution and thermal maturity, the extents of the play and resource in-place can be defined aerially for the numerous productive intervals of the Green River For- mation. Finally, we will address the key attributes of this petroleum system such that it may be used as a model for other possible lacustrine sourced unconventional oil resource plays.
