Shale Potential to be Tested
Gas Powering Utah Activity
Elk Petroleum’s “Nielsen 3-22,” True Rig 24, with Pelican Lake in the background, targeting tight gas sands in the Tertiary Wasatch Formation and Cretaceous Mesaverde Group, eastern Uinta Basin, Utah. More Utah Scenes
Photo by David Hackford, Utah Division of Oil, Gas & Mining
Utah is a happening place, where the industry action just keeps escalating.
“We’re seeing record drilling permits in Utah, mainly for tight gas,” said Tom Chidsey, petroleum section chief at the Utah Geological Survey (UGS). “Just last year, more than 2,000 drilling permits were issued, with most of these in the Uinta Basin area for gas.
“In fact, out of the 1,057 wells spudded in 2006, 656 were in Uintah County in the eastern Uinta Basin where the tight gas is,” Chidsey noted. “They’re going mainly for Wasatch and Mesaverde tight gas at depths from 7,000 to 10,000 feet.”
The 2006 permit numbers contrast markedly with earlier times. For instance, 253 drilling permits were issued in 1990 and 673 in 2000.
The presence of gas held hostage by tight sandstone reservoirs was recognized in this region years ago, but getting it out of the ground economically was not an option. Today, favorable commodity prices and advanced technology have vastly altered the economics of producing this resource.
Utah is the tenth largest producer of natural gas by state in the United States, according to the UGS, and most of it comes from the Uinta Basin, which produced more than 19 BCF in November 2006. Of this total, 14.1 BCF originated in the eastern part of the Basin at Natural Buttes field, which is the largest natural gas field in Utah.
Not to worry, there’s plenty left.
Estimates from the U.S. Geological Survey reveal that the Uinta Basin harbors reserves of more than 16 TCF of undiscovered, technically recoverable resources.
Tom Chidsey standing at Desolation Canyon in the southern Uinta Basin, with outcrops of Tertiary Green River and Wasatch Formations, and Cretaceous Mesaverde Group -- major hydrocarbon producers in the basin.
Photo by Craig D. Morgan, Utah Geological Survey.
Shale Gas Activity
If tight gas sandstones fail to excite you, another option is to take a look at shale gas, which also has the potential to become the next big thing for the prospectors.
Only a few years ago, there was plenty of talk about shale gas prospectivity but nothing to show for it. Some old wells -- think mid-1960s -- drilled into the shales, but operators lacked the expertise and technology to complete them to get good gas production.
Any production was serendipity for the most part, coming up the pipe as “add-on” gas.
The continuing speculation and rumors about the shales’ potential productivity encouraged consultant and AAPG member Steve Schamel to approach the UGS in 2004 seeking its support to undertake a study of shale gas in the state.
“There had been a few discoveries early on that no one had done anything with,” Schamel said, “and some consultants were out looking at possibilities for clients, but none of this information was being reported. So I proposed a project to the Survey to systematically look at the characteristics of these shales in the state.”
Schamel’s proposal was approved, and the results of the ensuing study have been published by the UGS.
The effort included a look at analogs of producing gas shales such as the Barnett, the Lewis shale in the San Juan and others to determine which shales had potential and for what reason.
“A lot of the shale in Utah is not prospective because it hasn’t reached a high enough degree of thermal maturity,” Schamel said. “It’s too late now because it’s being eroded away. In fact, many of these shales are close to the surface and not being buried.”
The good news is a few areas harbor shales that hold considerable promise for gas production. In fact, Schamel identified several organic carbon-rich shale units that appeared to have strong potential for commercial exploitation. These include:
- Several intervals of the 3,000-3,800 feet thick Mancos Shale of the Upper Cretaceous in the southern and central Uinta Basin.
- Black Shale intervals of the Pennsylvanian Paradox Formation in the deeper northeast half of the Paradox Basin.
- Manning-Doughnut Shale identified as Mississippian-Pennsylvanian boundary age, east of the Wasatch Front.
It is noteworthy that shale gas potential will comprise one of many topics to be included in the upcoming AAPG Rocky Mountain Section meeting, to be held Oct. 6-9 in Snowbird, Utah. A number of papers, posters, short courses and three field trips will be presented dealing with recent gas and oil developments in the region.
A Prairie Canyon member of the Mancos Shale forming low cuestas east of Green River, Utah. The top of the mesa is supported by the basal sandstones of the Blackhawk Formation.
Photo courtesy of Steve Schamel
Prior to Schamel’s study for the UGS, a few wells were producing “add-on” natural gas from wells completed in specific intervals of the Mancos. He noted several other Uinta Basin wells currently are producing natural gas from the Mancos Shale, but well records are being held confidential.
“The Mancos Shale gas play is now established, at least in the Prairie Canyon and Lower Blue Gate members,” Schamel said. “I anticipate that this play will expand very rapidly in the next few years.
“There’s a well about to be drilled for gas in the Manning Canyon shale,” he added. “I think before the end of the year someone will know if it has real potential for shale gas.”
There’s also considerable buzz among the prospectors over a couple of wells drilled by Delta Petroleum in its Greentown project in the Paradox Basin -- but mum’s the word from Delta.
“The company hasn’t come out and said they’re testing in the Black Shale units,” Schamel noted. “They’ve just described them as clastics, so I’m reserving judgment until I know what they actually completed in.
“One figure I saw looks very much like a profile through the Paradox Formation of the individual shale units,” he added. “It’s likely the shales, but it could be the sands, because in that part of the basin there are some thick sandstones.
“Delta is being very cagey, sitting tight on the well report.”
Chidsey noted “we’re getting a lot of inquiries about the discovery.”