ConocoPhillips Alaska has identified and controlled the source of a natural gas release which began March 4 at the CD1 pad at Alpine.
The company said in a March 24 update: “The natural gas that we are capturing from WD-03 is predominately methane and believed to be from the C-10 Halo formation, with lesser amounts from the Qannik formation. These low pressure, shallow formations are approximately 3,000 to 4,000 feet below the surface,” the company said.
On March 27 ConocoPhillips identified the C-10 Halo as the sole source of the gas, citing well logging results. The company said the CD1-03 well was being “restarted for water injection to promote a mitigation pathway for the natural gas while remediation activities on WD-03 take place.”
More importantly, the company said March 29: “WD-03 is no longer producing natural gas from the outer annulus due to source control operations that are in progress.”
The Alaska Oil and Gas Conservation Commission made the same observation in its March 29 situation report: “WD-03 is no longer producing gas due to source control operations.”
Release March 4
ConocoPhillips Alaska has been working to identify and control a natural gas release on the CD1 pad at its Alpine field on the North Slope since March 4 when gas was observed coming from the ground at the CD1-05 wellhouse. In situation reports the AOGCC said natural gas releases occurred at seven wells on the CD1 pad and through cracks on the pad near Doyon Rig 142. Oil production at CD1 was shut in.
The source was identified as a disposal well being drilled at the field, WD-03.
AOGCC said March 25 that plugging of the planned disposal section in WD-03 had been completed and that circulating kill weight fluid in WD-03 began March 28.
On March 30 AOGCC said source control was in progress, and that future plans include running and evaluating diagnostic logs, with results to determine how work will proceed.
All CD1 wells remain shut-in, AOGCC said, except for waste injection in CD1-01A and produced water injection in CD1-03 and CD1-05.
ConocoPhillips continues to monitor the CD1 well row for gas releases and well pressures, AOGCC said.
WD-03
In its FAQ page on the incident the company said it is common on the North Slope for shallow natural gas formations, with known natural gas production capability, to be present, occurring between 2,000 and 4,500 feet below the surface.
ConocoPhillips said the C-10 Halo zone of the WD-03 well was not cemented when WD-03 was drilled because “ConocoPhillips did not interpret this interval as a significant hydrocarbon zone” and thus it did not require cement per AOGCC regulations.
The WD-03 was permitted in January and Doyon Rig 142 was drilling the disposal well when the release was discovered; drilling activities at the well were suspended March 7 and the rig evacuated at a precaution.
Three hundred nonessential personnel were relocated, with some 100 remaining. Personnel have since returned to CD1 and Doyon 142 has been working on WD-03.
The company said total production from Alpine has been reduced by an average of some 8,000 barrels per day primarily due to the response measures.
On March 29 the Alaska Division of Oil and Gas approved a permit for a 3D seismic survey at CD1 (see story in this issue). ConocoPhillips said the survey, on and around the CD1 gravel pad, is to acquire data to evaluate the shallow subsurface characteristics in the pad area.
The survey, scheduled to begin March 29, was a result of the events at CD1, the company said, but because of the time required for data processing, the survey would “not inform the immediate CD1 natural gas release response efforts.”
- KRISTEN NELSON
