They might have to invent a new designation for the Anadarko Basin: “super-super basin.”
An extraordinarily deep basin, it towers far above the standard definition of a Super Basin – a basin containing multiple reservoirs and source rocks with cumulative production of at least 5 billion barrels of oil equivalent, and future production potential of more than 5 billion boe.
The Anadarko has all that and more, said Rick Fritz, industry consultant and president of Fritz Exploration and Production Co. in Tulsa. Fritz, a long-time Midcontinent geoscientist, served as AAPG’s executive director from 1999-2011 and is AAPG president-elect.
“The Anadarko Basin still has a lot of hydrocarbons remaining. With better commodity prices, another 50 billion boe could be discovered over time with horizontal drilling plus new conventional opportunities,” he said.
Those new opportunities include formations with underdeveloped potential as well as untapped reservoirs. Local geologists even speculate about a possible return to drilling vertical wells, driven by both economics and the basin’s characteristics.
Covering more than 50,000 square miles, the Anadarko Basin extends from west-central Oklahoma and the Oklahoma Panhandle into parts of southwest Kansas, southeast Colorado and the Texas Panhandle.
Recently, the Anadarko has been best known for its highly productive unconventional resource plays including the SCOOP, STACK and Cana-Woodford, and a multi-zone, mostly Cleveland sands play along both sides of the Oklahoma-Texas Panhandle border.
But the basin’s history of extensive and successful exploration stretches back to the early 20th century. Time and again, geologists have returned to this area for new hydrocarbon discoveries.
The Anadarko Basin is also a major producer of helium, and the only commercial source of iodine in the United States.
What Makes the Anadarko Special?
Fritz said several attributes make the basin an area of special interest for the oil and gas industry.
“Number one is the volume of hydrocarbons produced in barrels of oil equivalent. Almost 50 billion boe were produced from over 500,000 wells in the greater Anadarko Basin – the area contains 46 giant oil fields,” he noted.
“That includes the Oklahoma City and Panhandle fields plus the giant Hugoton embayment gas accumulation. The Anadarko Basin is really a natural gas giant, as two-thirds of the barrels-equivalent cumulative production is from gas,” Fritz said.
“Number two are the source rocks. The Anadarko Basin has multiple source rocks throughout the sedimentary section, source rocks with high TOC (total organic carbon) values and a favorable burial history and temperature profile – not too hot, not too cold,” he said.
The basin’s standout source, the Woodford Shale, is estimated to have generated more than 300 billion boe and “still has hydrocarbon-generating capacity and producing potential,” Fritz noted.
“The third characteristic is just the sheer volume of sediment and the number of reservoirs in the basin,” he said.
“Over 40,000 feet of sediment was deposited in the basin resulting in about 7,500 individual reservoirs and producing formations,” although some are the same with different names and zones, he observed.
Sediment in the Anadarko ranges from less than 2,000 feet to more than 40,000 feet at its deepest level, and the basin is home to a number of ultra-deep exploration wells. The deepest was the 31,441-foot Betha Rogers No. 1 dry-hole wildcat in Washita County, Okla., in 1974.
The Future of the Anadarko Basin
The Anadarko Basin still offers many attractive unconventional opportunities and its numerous source rocks remain potential targets, according to John Mitchell, consulting geologist for Rutherford Exploration in Fayetteville, Ark.
Mitchell’s career has included work as a senior geologist at both Apache Corp. and Newfield Exploration. He served as senior geologist-technical expert, Anadarko Basin asset team manager and exploration manager for SM Energy Company.
“There are source rock packages in the Anadarko Basin that are not as obvious as the Woodford,” Mitchell said.
“There are a lot of tight Pennsylvanian sands that are hydrocarbon-bearing. There are a lot of source rocks out there that have been overlooked because they aren’t ‘glamorous,’” he noted.
But Mitchell thinks the future of the basin might move away from unconventional resource plays.
“I’m not sure we’ll ever get back to the factory model” of continuous drilling, he explained.
“My guess is that the Anadarko will recover and go back more to the conventional or quasi-conventional model,” he said.
Fritz said “just about everything in the past 15 years in the Anadarko has been horizontal oil and related gas development. Conventional is out of vogue. But, that said, people are starting to look at conventional again.”
“There is a lot of 3-D seismic that was shot for unconventional plays that can be used to develop new conventional plays,” he added.
Depending on future economics, the basin also could see a resurgence of natural gas exploration and drilling, Fritz said.
“A lot of people now are looking at a long-term natural gas strategy. As a result, many of the plays will be followed down-dip into the deep gas zones,” he said.
Because of its variety, the Anadarko Basin offers multiple conventional and unconventional opportunities, in oil and gas, in both new and ongoing plays. The Granite Wash is an example of the established producers: a deep, liquids-rich tight sands play in western Oklahoma and the Texas Panhandle.
It’s one of the world’s largest resource plays in areal extent and covers the most ages of rock among Anadarko plays, from Cambrian through Permian.
Mitchell described the Granite Wash as “very meaningful,” even though it has received less attention than some other Anadarko plays. Also, a considerable area of the play’s acreage is held by existing production, he noted.
That’s less of a problem in other parts of the basin, according to Fritz. The Anadarko Basin generally offers large-scale tracts, lease turnover and industry-sophisticated minerals owners, he said. It also has few topographic issues and a long drilling history with plenty of good logs available, he added.
In recent years, “the Woodford Shale and the Mississippian carbonates and siltstones have been the primary horizontal targets in the basin. Companies are interested in the Springer-Goddard play, but it’s difficult to drill and fairly restricted in areal extent,” Fritz said.
“People are interested in the Viola shale and the Simpson shale, but they’re pretty restricted to the southeast portions of the basin and not as good as the Woodford. I’d say people are looking more at the Pennsylvanian right now—the Red Fork, Skinner, Oswego, Cottage Grove and Tonkawa sections,” he commented.
Fritz said the Pennsylvanian section “is very thick, overpressured and has resource potential -- the Cleveland-Marmaton was one of the early successful Penn plays in western Oklahoma and the Texas Panhandle.”
“In the eastern half of the basin we’ve been able to get a peek at the Pennsylvanian potential as we drilled through to the Miss and Woodford. For example, many wells have penetrated the prolific Morrow-Springer high-pressured section,” he noted.
Another major advantage for the Anadarko Basin is its history of technology development and detailed geology and engineering work. Seismic-reflection technology was developed in the Anadarko, and Vibroseis technology was advanced in the Conoco lab at Ponca City in the early 1950s, Fritz noted.
“The basin is a great laboratory. The technology that’s been developed is impressive,” he said.
“In some basins you may only see one or two waves of development over time. In the Anadarko there are multiple exploration and development phases resulting in a tremendous pile of data – logs, samples, cores, seismic – for research,” he added.
With so much to offer, a basin that’s been producing for a century might stay on the exploration map for another 100 years.
“As they say, ‘it’s a gift that keeps on giving.’ I’m sure the Anadarko super basin will continue to give well into the future, especially as economical commodity prices return,” Fritz said.
“There’s still a tremendous amount of hydrocarbons left in the Anadarko,” Mitchell observed. “The question is, how do we tackle it effectively and profitably?”