ConocoPhillips Alaska Provides Final Report on Alpine CD1 Natural Gas Release

The 2022 Alpine CD1 natural gas release was a unique event, with nothing similar ever occurring at a ConocoPhillips Alaska site. Going back over 20 years, we have drilled forty-nine wells through the C10-Halo interval on the CD1 pad without incident.

The WD-03 well at CD1 was constructed in accordance with regulatory requirements, including cementing and casing regulations. U.S. Environmental Protection Agency authorized construction of WD-03 as an Underground Injection Control Class 1 disposal well, in compliance with Safe Drinking Water Act regulations, and the Alaska Oil and Gas Conservation Commission (AOGCC) approved ConocoPhillips Alaska’s application for a permit to drill WD-03, in compliance with AOGCC regulations.

ConocoPhillips Alaska stood up an incident management team immediately on March 4, when the natural gas release was initially observed, and had a team of engineers and scientists working 24 hours per day to identify, control and remediate the release as quickly and safely as possible.

By March 8, ConocoPhillips Alaska had secured the location, determined the most probable gas source, and established a controlled flow path for the gas up the outer annulus (OA) of the WD-03 well into the Alpine Central Facility. This prevented additional release of gas into the subsurface strata under the CD1 pad, four days after the release was initially observed.

As of March 29, the flow of gas from the C10-Halo source was stopped, and controlled flow to the Alpine Central Facility was no longer required. The flow that occurred from the C10-Halo in the period from March 8-29 was captured by ConocoPhillips Alaska.

As of May 2, WD-03 was cemented to the surface, and operations with Doyon drilling rig 142 were completed. The rig was moved off location and, as of Dec. 6, 2022, the well was sealed with a welded steel plate in compliance with AOGCC regulations.

No gas was detected beyond the CD1 pad, no recordable injuries were reported, no damage to the tundra was observed, and no wildlife impacts were reported.

An investigation team determined that the cause of the natural gas release was a surface casing shoe in WD-03 that broke down when pressure limits were exceeded during freeze protect operations. The source of the release was determined to be from a shallow gas formation at the C10-Halo interval. The corrective actions include:

• Develop a standard freeze protect operating procedure for the North Slope with pressure limits and contingent solutions when pumping operations reach limits.
• Develop OA maximum pressure limits in the drilling program and communication protocols to the Wells Support Center and consider OA pressure sensors on drilling rigs to allow for alarms and/or trending.
• Review critical section plan operations with the personnel performing the work prior to execution, recognizing that section plan execution can occur across multiple personnel shift patterns.
• Conduct a review of the overburden and adjust the associated processes (i.e., log models) as necessary to improve identification of drilling risks, flowability assessments, and zones requiring cement isolation.
• Integrate additional well intervention and well integrity information into well planning (both pre-spud and during operations).

We submitted our final written report to the AOGCC on May 3, 2022 (see menu at right), and will incorporate learnings from our investigation into future projects and operations. Throughout this event, our primary concern was to protect the safety and well-being of our workforce, the local community of Nuiqsut, and the environment.