Recent releases of information from Pantheon Resources plc offered encouraging results on the Talitha A exploration/appraisal well drilled by affiliate Great Bear Pantheon on Alaska’s central North Slope, despite the fact well testing was interrupted by operational challenges resulting in the well being suspended until next winter when testing can be completed.
Reaching a total depth of 10,456 feet, the well encountered five stacked oil-bearing reservoir zones over a 3,700-foot interval which “management believes has validated its earlier assertion of over 1 billion barrels recoverable oil potential from this multi-billion barrel oil in place play at Talitha,” Pantheon said in its April 19 operational update.
“Testing of the deepest of these zones, the Kuparuk formation, which flowed high-quality light oil intermittently at rates up to 100 barrels of oil per day, a disappointing rate, encountered a number of operational issues. The Kuparuk horizon at this location was over-pressured which was both unexpected and unlike any known Kuparuk well regionally, which caused challenges in testing,” Pantheon said.
Why did Pantheon persevere with the Kuparuk and not abandon it and move to the shallower horizons?
Per its April 20 investor presentation, the Kuparuk was “too good to let go.” The company pointed to the “340 million barrel target with exceptional logs and gas chromatograph readings.”
The four normally pressured shallower Brookian zones, “all of which encountered light oil and offer excellent potential based upon analysis to date,” will be flow tested as early as next winter, dependent on a farmout, which the company has started.
In the meantime, the “enormous amount of drilling, logging and testing data” collected from Talitha A will be evaluated.
Kuparuk horizon testing
The Kuparuk proved more “geologically complex” than expected.
The well encountered more than 60 feet of “well-developed sand with high resistivity readings, indicating the presence of hydrocarbons,” Pantheon said.
Talitha A “demonstrated the key elements of a proven hydrocarbon system in the Kuparuk formation with the presence of movable high-quality (plus-42% API) oil. However, during testing the well-produced oil intermittently along with solution gas, with formation water fresher than anticipated,” the company said. “The 100 barrels of oil per day flow rates were not consistent with our expectation based on Talitha logs compared to nearby Kuparuk field production.”
A comprehensive analysis of the Kuparuk has already started, Pantheon said, “to gain a greater understanding of the atypical reservoir characteristics encountered” in Talitha A.
Early analysis “suggests that the Kuparuk horizon at this location might respond better to different drilling fluids and techniques,” Pantheon said.
The shallower horizons
The shallower Shelf Margin Deltaic horizon was the primary well target. The Kuparuk formation at this location is some 800 feet downdip from its ideal “updip” position, Pantheon said.
The reservoir qualities in the four shallower zones are “in line with expectations,” the company said. The oil “appears to be lighter than expected and an additional significant zone has been discovered, increasing the total resource potential significantly. These zones … will be tested next winter.”
From shallowest to deepest, the five oil bearing zones encountered in Talitha A are as follows: Shelf Margin Deltaic, Slope Fan System, Upper Basin Floor Fan, Lower Basin Floor Fan and Kuparuk.
The Basin Floor Fan zone was thicker than expected, encountering more reservoir, with the Upper BFF an additional zone with good reservoir properties.
The Slope Fan System was not as well developed as anticipated, however, but the company “now interprets that the SMD extends across the Alkaid project, and is better developed as it extends south east across the Dalton Highway,” Pantheon said.
Baker Hughes and Advanced Hydrocarbon Stratigraphy, or AHS, provided Volatile Analysis Service, or VAS, a “comprehensive, sophisticated and independent evaluation of hydrocarbon presence in the well bore, using mass spectrometry analysis of well cuttings.”
VAS entailed taking samples every 10-20 feet, “hermetically sealing approximately half of those samples to avoid any evaporation of hydrocarbons, with the other half of the samples tested after exposure to air,” Pantheon said.
These samples are subjected to mass spectrometry analysis in the Baker Hughes AHS VAS lab. VAS analysis confirmed the presence of continuous stacked oil-bearing reservoir zones. Every sample extracted oil, Pantheon said.
The company said it also used conventional data collection techniques including “Logging While Drilling, mud logging, side wall cores and an entire suite of wireline logs.”
Increasing resource estimate
Pantheon has started work on updating its resource estimates across the shallower Talitha A zones.
The discovery of oil in the Basin Floor Fan will become “an area of intense focus as this is part of the significant Theta West prospect, Pantheon’s largest target, now considerably de-risked” by Talitha A results.
“Theta West will test the exceptionally large Basin Floor Fan in a better structural location and hence should attract strong partner interest in drilling this significant prospect,” the company said.
A silver lining
“A great frustration is that we simply ran out of time to test all the zones. … when we … come back this coming winter, we will have the twin luxuries of a testing program incorporating the results of a thorough analysis of the dataset, and a much longer testing window. This can be accomplished with a small rig and at a much reduced cost,” Jay Cheatham, Pantheon CEO, said, which is especially good news combined with the fact this past winter’s drilling and testing of Talitha A came in one-third under budget.
