For those people who don’t work in the US onshore oil sector, names such as the Permian and the Appalachian may still sound familiar, as it is these basins that feature in the news so much. But what about the Uinta Basin? It was a new name for me, even though I must admit that I had visited some sites during a field trip to Utah more than 10 years ago. During the latest NAPE Conference, when asked about it, people were adamant, saying that the Uinta is the most prolific US onshore oil play at the moment.
So, why is the Uinta performing so well these days? The following things stand out.
“There is an extensive stratigraphic succession that has access to prolific and mature source rocks, ranging in age from the Cretaceous to the Tertiary Green River Formation. Basically, almost every foot of rock has got oil in it,” says John Sinclair, a geologist who has worked in the basin for five years.
The Unita is not a classic structural play either, with the oil being produced from four-way closures of a limited geographic extent. Instead, the biggest fields in the basin, the Altamont and Bluebell fields, should be considered as basin-centre deposits. “It’s not a big structure,” says John. “When you look at the map, you might think it is a big anticline or something like that, but it is just the deeper part of the basin, only with a few structural perturbations. There are no closures.”
The Uinta Basin also stands out for a very practical reason. “It is one of the few places I’ve seen where you can run a single-rig drilling programme and still ramp up production,” John says. “In other basins, you will see that production declines more rapidly than new production coming online through the completion of a new well, which requires more rigs to be involved to ensure growth. That is not the case in the best parts of the Uinta Basin, where newly drilled wells can easily achieve up to 3,000 barrels a day.”
Production in the Uinta started by drilling vertical wells into the deepest parts of the play. This has now evolved into operators drilling long horizontal wells that also require fracking. The water required for these operations is not of great abundance in Utah, but the flip-side is that most, if not all, the frack water is produced back so that it can be re-used.
And when it comes to water cut, that is also a factor that puts the Uinta in a good position. “Rather than in the Permian, where water cuts of 75 % are common, the Uinta hovers around 50 %. It is probably the high oil saturation and relative permeability to oil remaining quite high over time,” John argues.
What limits the Uinta Basin to increase production even more is the nature of the oil, which is quite waxy and cannot be transported by pipeline. It, therefore, needs to be either trucked to local refineries with limited capacity or hauled to the Gulf coast by rail,” says John, “which is not as cost-effective as local refining but still pays off.”
