Linc Energy Ltd. is cutting its winter exploration program at Umiat short because of a combination of mechanical problems and the approaching end of the Arctic winter.
The Australian independent postponed a planned flow test of the Umiat No. 18 vertical well it drilled this year at the oil field in the foothills of the Brooks Range after “an apparent blockage formed in the perforation tunnels during the early stages of the campaign,” according to the company. Attempts to clear the blockage were unsuccessful and Linc decided it could not return its rig to the pad with the time left before the thawing tundra restricts access to and from the remote drilling location.
Similarly, Linc deferred its Umiat No. 23H horizontal well to avoid stranding its rig on the tundra. The company is currently demobilizing equipment, and plans to cold-stack the Kuukpik No. 5 rig at the permanent Seabee drilling pad to get a jumpstart on next winter.
“While we are obviously very disappointed that we were not able to reach all of our objectives this season, we are very confident that we will be able to unlock the vast potential that exists at Umiat,” Linc Energy CEO Peter Bond said in a statement. “We will utilize the considerable lessons we have learned by undertaking drilling in the permafrost this year and, combined with the additional time available next winter due to the rig being stacked on location, to complete the appraisal of the potential of Umiat.”
After deferring its entire 2011 program because of weather and equipment delays, Linc planned a four-to-six well program for Umiat this winter, but low snow cover and extreme temperatures stole 45 days from the company early in the year, forcing it to defer more than half of its program, including plans to drill a Class II disposal well.
The revised plan called for drilling two wells — the vertical Umiat No. 18 and the horizontal Umiat No. 23H — into the same interval of the Lower Grandstand formation to collect core samples and provide “comparative flow testing” for economic purposes.
Even with the delays, Linc believes it can bring Umiat online by late 2017 and believes the field can produce up to 50,000 barrels per day into the trans-Alaska oil pipeline.
Pleased with core sample
After spudding the Umiat No. 18 well in early March, Linc collected some 300 feet of core starting at a depth of 710 feet. (The Umiat reservoir is infamously shallow.)
“The core was very obviously oil saturated in the positions that we expected there to be oil. In fact, the core was actually dripping oil. The core varied in color from a light gray to a black. We passed it under a fluorescent light as a test to indicate the presence of oil, which it did indicate,” said Scott Broussard, Linc’s president of oil and gas operations.
The core sample was the first taken through the entire Lower Grandstand at Umiat with complete recovery, according to Broussard. The sample is currently at a lab in Houston, Texas, where it is being evaluated for permeability, porosity and other geologic metrics, but Linc previously said an early evaluation suggested some 100 feet of net oil pay.
Flow test compromised
After setting intermediate casing through the Lower Grandstand formation, Linc continued drilling to a depth of 2,600 feet to test for natural gas identified by a seismic anomaly. The prospective sands ended up being “low in permeability and not productive.” While Linc believes it has “a number of options” to bring gas to Umiat to maintain oil pressure, the company said it would prefer to have an onsite supply.
Upon reaching target depth, Linc plugged Umiat No. 18 below the Lower Grandstand for the purposes of a flow test. Oil initially flowed to the surface, but soon ice and other debris blocked the well. “Site operational teams employed multiple techniques to clean the perforations including methanol, solvents and surfactants to remove any ice or other debris,” but failed to resume the flow before the end of the season, according to Linc.
The results fit with previous Umiat exploration.
In a 1960 study of the 11 Umiat wells drilled to date, U.S. Bureau of Mines petroleum engineer Oren C. Baptist blamed the “unpredictable” results of the wells — such as a dry hole located 200 feet from a 400 barrel per day well — on geology and engineering.
Chilled mud system
The Umiat reservoir is shallow, of low pressure and partially frozen in permafrost, and Baptist hypothesized that warm drilling mud used in the drilling process had thawed the permafrost, allowing water to seep into the formation, freeze the sand and plug the wells.
Considering those earlier results, Linc devised a chilled mineral oil based mud system for drilling, which it believes worked well, and utilized a “progressive cavity pump” for its flow test “in order to prevent heat in the borehole from establishing a ‘thaw bubble’ in the permafrost and potentially destabilizing the well bore and surface facilities,” according to Broussard. “We were also careful to make sure that the pump was below the perforated zone in order to make sure that heat was not introduced at the perforated zone,” he said.
Linc presumably believes the casing and/or perforations contributed to the problems with the flow test because the company said that it intends to use an open hole completion technique at its future vertical wells at Umiat and a technique that replicates the open hole technique for its future horizontal wells. In an open hole technique, the absence of casing or lining allows fluids from a reservoir to flow directly into a well bore. The U.S. Navy used an open hole completion technique on its original wells at the Umiat field.
“We believe that we have a range of solutions to address the problems encountered this year and that the lessons learned will assist Linc Energy greatly when moving forward into the December drilling campaign at Umiat, later this year,” Bond said. “The early indications, given the success of the historic wells, are that the solution may be as simple as drilling and completing the well in an open-hole configuration. We also believe that horizontal wells, given the increased surface area relative to the reservoir, provide the best solution to unlocking the potential of this world-class asset.”
