Gas hydrates are a flow assurance problem in flowlines, but when found in natural accumulations in the ground, methane hydrates represent a potentially vast energy resource. For example, the US Department of Energy estimates that Alaska's North Slope may contain 590 tcf of methane in this frozen form, a much greater volume than it estimates for North Slope conventional gas resources.
To test whether this methane ice is producible, DOE entered into a 2 year project with Anadarko Petroleum Corp., Maurer Technology Inc., and Noble Engineering & Development. Maurer and Noble Engineering & Development are both subsidiaries of Noble Corp., Sugar Land, Tex.
For the project, DOE is providing $6 million of the $10.5 million total estimated cost and half of the additional $2 million needed for deploying and testing a prototype lightweight aluminum drilling platform.
Anadarko operates the project and spudded the test well, Hot Ice 1, on Mar. 31, south of Kuparuk River field and 60 miles west of Deadhorse, Alas.
Test features
The 100 ft by 100 ft platform sits on steel legs about 12 ft above the tundra. The elevated platform eliminates the need for gravel pads, thus reducing the impact of drilling on the fragile ecosystems found on the North Slope.
The 133/8-in. diameter platform legs are made of arctic-grade steel. The legs were inserted into holes drilled about 20 ft into the tundra. Each leg weighs about 2,500 lb.
The platform has a modular construction, with the modules moved to the site during winter across the tundra on Rolligon all-terrain vehicles with fat rubber tires that exert just a few pounds of weight per square inch. Anadarko envisions that future models of the platform will allow some equipment to be moved by helicopter.
On location is an Australian-built Dynatec UDR 1500 Series rig that has a special arctic-grade mast and is capable of coring or drilling to about 3,000 ft with CHD 134, 5-in. drill rods and to about 6,000 ft with small pipe. The mast hoist has a 60,000 lb pull capability.
Anadarko expects to encounter the objective methane hydrates at 1,200-2,500 ft.
The main platform consists of 16 aluminum modules with five more modules for the crew quarters. Each module is 121/2 ft by 50 ft by 3 ft and weighs less than 20,000 lb, including the top deck covering.
The modules interlock "like Lego pieces," according to Anadarko.
Anadarko said it took about 1 month to assemble the platform and about 1 month to assemble all the topsides equipment and facilities, including the rig, the crew quarters, the laboratories, etc.
The coring to date was done with CHD 134 drill rods, 5-in. flush OD coring string weighing 14.4 lb/ft, and 57/8-in. polycrystalline-diamond compact core bits that have a 31/4-in. inner kerf (core diameter) and face discharge ports. The drilling fluid was a polymer mud chilled to about 26° F. to control the stability of the permafrost and the cores.
Core was cut from 840 ft to the top of the methane hydrate at 1,400 ft in the hole. After this, the work involved opening the hole to 81/2 in. to 1,270 ft, logging the hole, and setting and cementing a 7-in. casing string.
A Noble Engineering & Development system called Drill Smart allowed the team to monitor the entire operation and transmit the data live to Houston.
Waiting for the test
Anadarko shut down the operation Apr. 21 because of unseasonably warm weather, but it expects to resume working on the well in the fall during which time it will attempt to produce the hydrate zone. The rig will remain on location until the production test.
Anadarko plans for the production test involve depressurizing the hydrate zone to test the inflow of gas and water volumes. The test will include surface readout gauges in the wellbore and a heated tubing string.
A surface separator and a gas and liquid measurement skid with a flare stack hook-up will also be installed for the test.
If successful, the test may herald the start of a new phase for the energy industry.
