Stuck tubing stops North Shore Sag test

Coiled tubing lodged in the wellbore prevented BRPC and partners from testing Sag River formation; details emerge from Tofkat No. 1

Kay Cashman & Eric Lidji

Petroleum News

Expounding for the first time on the mechanical troubles hinted at earlier in the year, the Canadian independent TG World Energy said May 15 that coiled tubing stuck in the North Shore No. 1 well prevented testing on one of the two target formations this winter.

Brooks Range Petroleum Corp. ran the exploratory drilling program on Alaska’s North Slope this past winter on behalf of a joint venture with TG World, Nabors subsidiary Ramshorn Investments Inc. and Bow Valley Alaska Corp.

“The coiled tubing became stuck in the hole before a production test could be conducted on the Sag River formation; a zone with approximately 20 feet of oil pay with no water line encountered,” TG World said in a release on May 15.

Hoping to regain full access to the Sag River formation, BRPC attempted a fishing operation from April 22 through May 6 using Nabors rig 27E.

BRPC recovered a 700-foot portion of tubing from the wellbore, but warmer weather “made it necessary to suspend the well and leave the remaining tubing in the hole,” according to TG World.

BRPC released the Nabors rig from its contract May 7.

With coiled tubing “stuck across the zone of interest, diesel was pumped into the well, which was then opened to flow,” TG World said. “The well flowed for 18 hours at an average rate of 50 barrels per day of diesel cut oil. Pressure transient analysis of the flow test and several step-rate pump-in tests indicate that the 22 foot interval of completion perforations was severely damaged.”

Without that damage to the perforations, BRPC predicted that the well would have flowed at “10 to 20 times the actual rate or 500 to 1,000 barrels of oil per day” from the Sag River formation, making the total flow from the Ivishak and Sag River formations in the neighborhood of 2,592 to 3,092 barrels of oil per day.

“Specific well work to confirm commercial rates” from the well is “being formulated,” TG World said. The company also said development planning work for the North Shore prospect has begun “to determine the optimal recompletion or sidetrack strategy for North Shore No. 1, in the context of an overall commercialization plan.”

The stuck tubing did not prevent the companies from testing the Ivishak formation in the North Shore well, northwest of Prudhoe Bay. The Ivishak formation flowed at a “stable oil flow rate” of 2,092 barrels of oil per day of 34 degree API oil for five hours.

Details from Tofkat

Taking 10 oil samples from four different sandstone reservoirs using a modular formation dynamics testing tool, the companies found 22.9-24.0 degree API oil in the Brookian Topset 1 at 6,128 feet, followed by 13.4-14.7 degree API oil in the Brookian Topset 2 at 6,294 feet, then 36.6-38.2 degree API oil in the Brookian Turbidites at 11,000 feet and finally 41.8-42.0 degree API oil in the Kuparuk zone at 11,943 feet.

That final Kuparuk zone showed similar properties to the Kuparuk Nanuq field oil and indicated six feet of net pay, according to TG World.

“The Brookian Turbidite light oil zone appears to be in a low porosity reservoir where penetrated; this formation is productive in nearby fields where better sandstone facies are developed,” the company said.

Finally, “The heavier oil properties for the two shallower reservoirs are characteristic for the North Slope; these sands were in low porosity reservoirs where penetrated, but are productive in nearby fields where better sandstone facies are developed.”

TG World said the joint venture plans to use 3-D seismic acquired this winter to map for “indications of offsetting areas of better quality reservoir development to these oil zones.”

BRPC drilled Tofkat No. 1 and two subsequent sidetracks using the Nabors rig 27E.

The company is currently analyzing seismic data in preparation for the 2009 winter drilling season. Until then, the company plugged and suspended Tofkat No. 1.