Vol. 26, No.9 Week of February 28, 2021
Providing coverage of Alaska and northern Canada's oil and gas industry

ConocoPhillips says Harpoon 2 dry but prospect still promising

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Kay Cashman

Petroleum News

In its Feb. 21, 10-K 2020 annual report, ConocoPhillips expensed its North Slope Harpoon 2 exploration well as a dry hole after “evaluations confirmed the well intersected sub-commercial volumes of hydrocarbons in the upper Harpoon interval which will not be developed.” But the company still views the prospect as having commercial potential and intends to do more drilling there in the future.

In the National Petroleum Reserve-Alaska, Harpoon 2 was one of three Harpoon prospect wells that were supposed to be drilled in the 2020 winter drilling season. But the drilling season was cut short due to concerns for worker safety connected to the coronavirus.

ConocoPhillips appraisal of the Willow oil discovery in the Bear Tooth unit in NPR-A also ended early with the drilling of two of four planned wells, per the 10-K NYSE filing.

The reduced 2020 Willow appraisal program “consisted of drilling a horizontal well in the eastern portion of the field, informing the reservoir’s connectivity, and a vertical well in the field’s southern extent, reducing the original oil in place uncertainty,” the company reported.

The initial development plan for the Willow discovery, approved in the fourth quarter, did not include the Cassin discovery from 2013; “therefore, we recognized dry hole expense for two previously suspended Cassin wells in 2020,” ConocoPhillips said in its filing.

In its description of the winter 2020 exploration of the “Harpoon Complex - Harpoon, Lower Harpoon and West Harpoon,” ConocoPhillips said “future exploration plans include returning to the Harpoon Complex to explore the remaining potential.”

One of the North Slope’s most successful explorers, Bill Armstrong, has leased acreage to the west of Harpoon, confirming his bullish view of the exploration outlook for the area.

Remember what Matt Fox said

In its first quarter 2020 earnings webcast ConocoPhillips Executive VP & COO Matt said it appears that the Harpoon 2 well “clipped the edge of the topset based on its log response. … We won’t know that for sure until we get a chance to drill the second well,” a reminder that ConocoPhillips executive Michael Hatfield said in November that 3D seismic imaging indicates Harpoon has “high-potential Brookian topset targets with stacked plays.”

When asked about encountering hydrocarbon fluids in Harpoon 2, Fox said: “Yes, we did encounter hydrocarbons. … It looks from a lithological perspective similar to other lithological signatures we’re seeing on the edge of these topsets.”

More exploration, Brookian sequence

Finally, in its Feb. 16 10-K 2020 annual report ConocoPhillips also reported that a 3D seismic survey was completed in 2020 over a 234-mile area of the region on state and federal lands, noting it was “currently evaluating this seismic data for future exploration opportunities.”

What it and others are chasing appears to be the Nanushuk formation, which forms part of the Brookian sequence, the youngest and shallowest of the major North Slope petroleum bearing rock sequences. Although rocks of the Brookian are found across the entire North Slope, the Nanushuk is found mainly west of the central Slope.

The rocks of the formation were generated from sediment pouring from the west into an ancient marine basin. As these sediments accumulated on and down the basin margin, the margin migrated from west to east, eventually coming to a halt at what is referred to as the ultimate shelf margin, a few miles to the east of what is now the Colville River delta.

Following the discoveries of the Prudhoe Bay and Kuparuk River fields in rock reservoirs much older and deeper than the Nanushuk, subsequent exploration mainly focused on these deeper rocks, with Brookian strata such as the Nanushuk generally being ignored. Until that is, 2015, when Armstrong Oil & Gas Inc. and partner Repsol E&P USA Inc., taking a contrarian view of conventional North Slope exploration strategies, made the Pikka discovery to the east of the Colville delta. (Oil Search and Repsol own the working interest in Pikka today.)

That discovery upended expectations for potential oil volumes in the Brookian.

The Nanushuk oil reservoirs consist of a series of sand bodies that were deposited at the top and down the upper slope of the ancient marine basin margin, as that margin migrated east. While the sand bodies can be identified in seismic cross sections, anomalously high seismic amplitudes, particularly in high resolution 3D seismic, can point to potential oil accumulations.

U.S. Geological Survey geologist Dave Houseknecht told Petroleum News in May that these potential oil reservoirs have distinctive geometries. Some, such as those of the Pikka discovery, tend to be thick but narrow, fairly elongated and generally oriented north to south. Others, such as ConocoPhillips’ Willow discovery tend to be more oval in shape. He said the different geometries may lead to different reservoir performances.


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