The unconventional Uinta Basin shale play in Utah has been called “quirky.”
Call that an understatement.
It didn’t take long for oil and gas operators to realize there are two types of unconventional resources: the more “conventional” and common unconventional plays, and a variety of other types.
Conventional unconventionals still dominate development activity and production, but lately the oil and gas industry has seen an expanding interest in less-typical unconventional plays.
This month’s Unconventional Resources Technology Conference in Houston will include presentations on both kinds of plays – with an interesting sample of the un-unconventionals.
A Wednesday morning June 19 session, “Emerging Plays and Challenges,” offers a pair of presentations on lacustrine shale plays. It’s an antidote to thinking the unconventional world is all about dark marine shales or tight sands.
Both involve the basin remnants of huge, ancient lakes, one site in present-day China, the other in the United States, in Utah and Colorado.
The ‘Next Great Play’
“Unpacking the Uinta Basin: The Next Great Oil Play?” will look at this growing unconventionals play, where operators have boosted production several years in a row. It combines prolific stacked-pay possibilities with several unusual features.
If nothing else, the phrase “next great oil play” is a grabber.
“Unconventional plays in the Uinta Basin have a number of unique geological characteristics because of the lacustrine geological setting,” said Ted Cross, vice president of product management for Novi Labs in Austin and co-author on the presentation paper with Josh Sigler and Lucas Fidler of XCL Resources.
“But despite those differences, it shares a lot in common with other plays like the Permian or Bakken. We say ‘next great’ play because of the well results and tremendous stacked pay in the basin,” he added.
Cross and his fellow authors identified outstanding productivity potential in multiple Uinta zones, primarily in the Uteland Butte and Lower Green River formations, with additional targets in the basin’s Wasatch and Middle/Upper Green River formations.
Stacked deposition of deep lacustrine source rocks enables operators to target multiple benches of the Green River and Wasatch/Colton formations, they note. Horizontal development yields as many as 17 horizontal wells within a 1,280-acre development unit, “with several thousands of feet of lacustrine pay left to be developed.”
Like many other unconventionals, key play variables include total porosity, oil in place and depth as a proxy for pressure and maturity, the authors noted. Lateral length and completion design are both major factors in Uinta well productivity, they found.
“The maturation of the source rock generated overpressure in parts of the basin, which improves well performance,” Cross said.
That’s all normal so far. But Uinta shale oil is a high-API gravity, paraffinic waxy crude that ships by truck or rail, not pipeline. Moving that oil out of the basin has challenged and bedeviled operators in the past.
“The Uinta geology is unique compared to other U.S. unconventionals because of its lacustrine setting and extreme source richness. The crude oil also has a high wax content, which makes it solidify at room temperature,” Cross noted.
Also, Uinta oil is abnormally low in contaminants, low in sulfur and metals and nitrogen. Operators and refiners have promoted it as an environmentally friendly alternative to other available crude in the region. Refiners prize the waxy crude as feedstock for producing lubricant base stocks and low-sulfur fuel. (Note: Uinta shale oil is unrelated to Utah oil shale, rock that must be heated to covert its kerogen content into oil.)
But environmentalists have taken an oddly specific dislike to Uinta production. They’ve challenged plans to build a proposed Uinta Basin Railway, primarily designed to carry the waxy oil to a rail link toward Gulf Coast and West Coast refineries. A court order last year blocked construction on the project.
Meanwhile, other transportation options have improved and Uinta producers look to have even more room to increase output. Utah oil production reached a record total of more than 56 million barrels per year in 2023, according to the U.S. Energy Information Administration.
“Comparatively, the basin’s productivity aligns closely with that of the Delaware and Williston basins, indicating its competitive stature in the unconventional oil play landscape. Expected long-term development density ranks above the Williston but slightly below the Permian,” the authors wrote.
They based their projections on statistical analysis of completions, spacing and subsurface characteristics, then used a machine learning approach to develop an overall play assessment.
“We trained machine learning models using Novi Labs software. These models learn what drives production across geology, completions, spacing and parent-child relationships. They are able to predict withheld data in the basin with strong accuracy, similar to other basins,” Cross said.
Sichuan Basin Insights
The same URTeC session on emerging plays includes the presentation, “Geological Insights into Lacustrine Shale Oil and Gas: The Jurassic Ziliujing Formation in China’s Sichuan Basin.” Several researchers from Chinese institutes have compiled an analysis of this potential unconventional play.
Their work focuses on the lacustrine shale characteristics of the Dongyuemiao and Da’anzhai sections of the Ziliujing. The Da’anzhai member, especially, has been cited as a high-potential target in previous studies, with shows of both oil and gas.
Two sets of organic-rich shale are present in the Ziliujing, characterized by varied mineral composition associated with interlayer lithology, the researchers found. Total organic carbon, shale porosity and interlayer porosity were key indicators in evaluating source-storage coupling, they wrote.
Argillaceous shale shows the most effective coupling, they noted, along with shell-bearing calcareous and silty shales.
With multiple shale prospects, including its lacustrine deposits, the Sichuan Basin has become a center of unconventional resource development in China. Another June 19 URTeC presentation examines a different play in the basin, “Geological Controls and Characteristics of Shale Gas Sweet Spots in Sichuan Basin’s Reservoirs.”
In addition to describing this unconventional gas resource, the study addresses an intriguing question: What contributes to the development of sweet spots in shale plays?
Research focused on the interaction of organic richness, lithofacies and preservation in shaping pore development and sweet-spot formation. Among other findings, it showed that local preservation conditions produced significant variations in initial production and estimated ultimate recovery.
In both the Uinta and Sichuan basins, understanding the geological parameters of shale plays is essential to understanding their potential development, the studies found. That’s especially true in light of their lacustrine histories.
Asked to identify the best and worst aspect of Uinta shale, Cross replied, “The play has, one, excellent well performance and, two, many stacked targets, which makes for a great play.”
“As far as worst – I’ll just say that it’s misunderstood, both from an offtake-infrastructure perspective and from a geological perspective,” he said.