For decades, three natural gas fields near Barrow have allowed the largest city in the North Slope Borough to avoid the crippling energy costs plaguing much of rural Alaska.
The production comes from three fields: South Barrow, East Barrow and Walakpa.
The U.S. Navy discovered South Barrow with the 2,505-foot South Barrow No. 2 well in 1948, during its initial wave of National Petroleum Reserve-Alaska exploration. Production began the following year, but development continued for decades, with 13 wells drilled through 1987, according to the Alaska Oil and Gas Conservation Commission. The field peaked at some 3.5 million cubic feet per day in 1980 and 1981.
In the early winter months of 2012, South Barrow was still producing 1 mmcf per day or more, but production rates have been lower in 2013. Cumulatively, the field produced nearly 24 billion cubic feet of gas through July 2013, according to the AOGCC.
The original estimate for the field was some 32 bcf of natural gas.
East Barrow discovered in 1974
The U.S. Geological Survey discovered the East Barrow field with the South Barrow No. 12 well in 1974, during the second wave of NPR-A exploration. Regular production began in December 1981, but drilling continued through 1990, with eight wells altogether. East Barrow production initially peaked at some 2.75 mmcf per day in early 1984.
In the winter of 2012, East Barrow production ranged from 200 thousand cubic feet to 900 mcf per day, with production in the winter of 2013 holding at a steadier rate of about 350 mcf per day. Cumulatively, the field produced more than 8.8 bcf through July 2013, surpassing the original estimate of 6.2 bcf of gas in place.
The reservoirs for the South Barrow and East Barrow fields are located in a stratigraphic setting similar to the Alpine field some 135 miles to the east. The third field, Walakpa, is in the Pebble Shale unit, a major North Slope petroleum source rock.
Working under a Navy contract, Husky Oil discovered Walakpa with the 3,666-foot Walakpa No. 1 in the 1980s. Production began in the early 1990s. The field has peaked above 5 mmcf per day numerous times over its history, including earlier this year.
Cumulatively, the Walakpa field had produced nearly 25 bcf through July 2013, according to the AOGCC. The field is believed to hold some 250 bcf of gas.
Drilling program
The three fields have kept Barrow warm and lit for more than half a century, but eventually the demands of those long Arctic winters started depleting the wells.
In recent years, the community realized it needed to improve deliverability at the Barrow gas fields if it wanted them to accommodate the expected growth in future demand. So the North Slope Borough launched a program in 2010 to drill as many as six wells at East Barrow and Walakpa, and to plug and abandon as many as eight depleted wells at the two fields.
After voters approved two bond sales, the borough launched the $92 million program in 2011, conducting a major summer sealift and starting drilling activities through that winter.
Over the course of the winter, the borough ultimately used the Kuukpik No. 5 rig to drill five horizontal wells — the first wells to be drilled horizontally at the fields. These were the Savik 1 and 2 wells at East Barrow and the Walakpa 11, 12, and 13 wells at Walakpa.
The program also included an effort to upgrade aging gas pipelines and install modern wellhead housing at the fields, which not only improved the integrity of the infrastructure but has also allowed the community to increase deliverability by increasing pipeline pressures.
The program successfully plugged and abandoned the eight depleted wells, but the community would like to someday plug a nearby legacy well and convert an older well for disposal.
The greatest accomplishment of the program in the short term has been to give Barrow some breathing room during winter weather emergencies or future well problems.
Production varies considerably from winter to summer: According to figures provided by the municipality, production averaged 5.9 mmcf per day in January of 2013, and 2.9 mmcf per day this June.
Previously, Barrow was forced to rely on expensive diesel fuel when field maintenance required engineers to take multiple wells offline at once. Now, the combined production from the new wells far exceeds peak winter demand. As such, “we can essentially meet the coldest day demand for Barrow with two of the Walakpa wells,” Dudley Platt, oil and gas liaison for the North Slope Borough, told Petroleum News in August 2012.
From a technical standpoint, the results from the drilling campaign convinced the AOGCC to slightly expand the area of the Walakpa gas pool based on new information.
Are hydrates producing?
The program may also have produced an unexpected outcome.
In the early 2000s, when East Barrow production surpassed its original gas in place estimated without reservoir pressure declining, geologists began wondering whether methane hydrates might be “replenishing” the conventional gas reservoir at the field.
Within a certain range of temperatures and pressures, such as those across much of the North Slope, methane molecules can become trapped inside “cages” of ice. A change in temperature or pressure can “unlock” these hydrates, yielding huge volumes of methane.
The geologists wondered whether the normal decline in reservoir pressure from sustained East Barrow production was “unlocking” hydrates, which in turn increased field pressure.
A preliminary study in 2006 suggested the East Barrow and Walakpa reservoirs might exist at least partially within the stability zone required for producing hydrates. The U.S. Department of Energy announced plans to drill a well at East Barrow to test those suspicions, but withdrew funding for the project in 2010, leaving the matter inconclusive.
While other test wells in northern Canada and Alaska have shown the technical feasibility of depressurizing hydrate reservoirs to stimulate production, the tests have yet to demonstrate the commercial viability of this method. With the Barrow upgrades, “We believe we have the first commercial gas hydrate production in the world,” Platt said.
