USGS prepares new assessment of Delaware Wolfcamp

From the Midland Reporter-Telegram

By year’s end, Permian Basin oil and gas producers active in the Delaware Basin should have a better idea of the undiscovered, technically recoverable resources in the Wolfcamp Shale and Bone Spring formations.

Stephanie Gaswirth with the U.S. Geological Survey’s Central Energy Resources Science Center, told those attending the recent West Texas Geological Society Fall Symposium that the agency will release its assessment by the end of the year.

She declined to discuss any findings before the assessment is released, but said the assessment focuses on the Delaware Basin portion of the Permian, as opposed to the assessment released in 2016 that looked at the Midland Basin portion of the Wolfcamp and Spraberry formations.

The agency said in 2016 that the estimated resource for the Wolfcamp and Spraberry in the Midland Basin was 24 billion barrels, at the time the largest domestic continuous oil assessment the survey had issued to date.

Gaswirth described how the agency conducts its assessments and the challenges it faces in assessing resources.

“We emphasize technically recoverable,” she said. “We look at the resources extracted today. We don’t do economically recoverable resource estimates; this is not an in-place resource estimate, it’s not a reserves estimate.”

In 2007 when the USGS issued its last assessment, it found 100 million barrels in five conventional formations in the Bone Spring, Spraberry and Wolfcamp formations. At the time, wells producing from those formations were primarily vertical, and in the ensuing 11 years there has been a huge shift to horizontal wells, she said.

She said the Delaware Basin differs from the Midland Basin in that its strata is deeper – 16,000 feet to the top of the Strawn, compared to 9,500 feet in the Midland Basin. The Wolfcamp formation is thicker by thousands of feet, and the Delaware has a higher thermal maturity, she said.

In assessing the two formations, the USGS identified and utilized 11 assessment units: the Delaware Basin Wolfcamp D continuous gas, the Delaware Basin Wolfcamp C continuous gas, the Delaware Basin Wolfcamp C continuous oil, the Delaware Basin Wolfcamp B Lower continuous oil, the Delaware Basin Wolfcamp B Upper continuous oil, Delaware Basin Wolfcamp A continuous oil, Third Bone Spring continuous oil, Second Bone Spring continuous oil, First Bone Spring continuous oil, Lower Avalon Shale continuous oil and Upper Avalon Shale continuous oil.

According to Gaswirth, the challenges in assessing the Delaware lie in stratigraphic nomenclature. Some operators have different names for the formations and their benches, she said. Another challenge was obtaining the landing zones for horizontal wells to determine which assessment unit they fell into and establishing the division of the Wolfcamp and Bone Spring units based on geologic criteria. Another question to be answered in the assessment was where, vertically and spatially is the transition from gas to oil, she said.

“The Delaware Basin is an anomaly in that its higher thermal maturity is to the west despite the uplift,” she said. “The deepest basin adjacent to the Central Basin Platform is the least mature.”


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