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Evaluating the Foothills natural gas Anadarko knows the gas is there but needs to assess volumes and production characteristics before making a development decision Alan Bailey Petroleum News
It’s one thing to know that there are gas fields in the ground but quite another matter to determine that those fields can be viably developed. So, when it comes to the known gas fields in Alaska’s Brooks Range Foothills, Anadarko Petroleum, together with its partners Petro-Canada and BG, is engaged in a multiyear resource evaluation, Doug Wilson, Anadarko’s Alaska exploration manager, told the Resource Development Council of Alaska’s annual conference in November.
Anadarko is now working on the second season of a Foothills drilling program that consists of two phases, Wilson said. The first phase, involving two or possibly three drilling seasons, is designed to understand the nature of the gas resource and the reservoir deliverability. The second phase, consisting of field appraisals, will likely take several seasons more, Wilson said.
Delineate gas pools Wilson said that the Foothills gas fields typically occupy what geologists term “four-way closures,” hydrocarbon traps formed in situations where the rock strata have been deformed into dome-like structures. Most of the exploration wells that discovered the fields in the late 1940s and in the 1950s drilled into the tops of these structures, Wilson said.
“We really need to understand whether the gas is just confined to those traps. Or does it go off the structures in between some of them? How big is the resource out there?” Wilson said.
Anadarko also needs to understand the likely economic performance of production wells in the fields. Developing these well performance forecasts entails an understanding of likely production rates and well spacing, as well as estimates of how long production would last and an assessment of possible production problems, Wilson said.
“Those are things we really need to understand before we pour billions of dollars into a project like this,” Wilson said.
Drilling seasons The first drilling season of the first phase of the Anadarko Foothills exploration took place in the winter of 2007-08 and saw the completion of the Gubik No. 3 well and the partial drilling of the Chandler No. 1 well. Both wells lie east of the Colville River near Umiat.
The second drilling season, to be conducted during the 2008-09 winter, will entail the completion of the Chandler well and the drilling of two new wells, Gubik No. 4 and Wolf Creek No. 4. Wolf Creek lies about 40 miles west of Umiat.
The Nabors rig 105-E that started drilling the Chandler No. 1 well last winter spent the summer on an ice pad at the Chandler location, ready for a three-to four-week jump start on continuing to drill the well this winter.
“We got down to about 1,900 feet last year and we want to go back and drill that well to about 10,800 feet,” Wilson said.
Anadarko will then move the Nabors rig to drill the Gubik No.4 well, for a down-dip test of the Gubik field. Because of the number of wells that have already been drilled in the Gubik field, Gubik No. 4 is more of an appraisal well than the other wells that Anadarko is drilling — Anadarko wants to determine the extent of the field reservoir and features of the field such as the fluid contacts, Wilson said. The Gubik No. 4 well will bottom out at around 4,400 feet.
Wolf Creek While the Nabors rig is in action at Chandler and Gubik, the Doyon Arctic Fox rig will deploy to the Wolf Creek field to drill the Wolf Creek No. 4 well to about 4,000 feet. The rig will spend the season at Wolf Creek, conducting tests to obtain information about field deliverability, Wilson said.
And as part of the complex logistics involved in carrying out a drilling program in a remote part of northern Alaska, Anadarko will have to construct 82 miles of ice roads and 80 miles of snow roads this winter. Moving equipment to and from drilling sites will involve multiple river crossings.
“One of the big challenges is going to be moving all of this equipment on and off the tundra at the same time,” Wilson said.
Anadarko plans to build an insulated ice pad at Gubik, to retain the option of staging equipment on the tundra over the summer. The company also plans to build a conventional ice pad at Wolf Creek to support the operations there.
Field economics In addition to understanding the technical parameters of the gas fields, Anadarko needs an understanding of the economics of developing the fields before the company can make any development decision — Anadarko has also been using its expertise from the Rocky Mountains region to develop conceptual designs for Foothills gas field facilities, Wilson said.
And a pipeline for exporting gas from northern Alaska is obviously critical to the commerciality of Foothills gas. Two proposals for a future North Slope gas export pipeline are currently in progress, while there is also the possibility of a pipeline for delivering Foothills gas into Southcentral Alaska.
But Wilson also emphasized that any development project in the Brooks Range Foothills needs to compete for capital in Anadarko’s global portfolio of development opportunities. For example, the company is planning to drill about 20 wells in different basins in the Lower 48, Wilson said.
“We have a lot of different opportunities around the world that we’re working on,” he said.
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