New rig designs tackle a host of difficult conditions.

As access to the world's oil and gas reserves becomes constrained outside Europe and North America, the interest in and potential for exploration and production (E&P) in remote regions has increased. This is especially true in the Arctic frontier, where E&P spending is forecast to grow significantly. The Sakhalin Island shelf contains proven reserves rivaling the North Sea during early development, and 80% of Russia's potential hydrocarbons are concentrated in the northwest Arctic shelf.

In this environment, the development of drilling technology for extremely harsh cold weather envrionments plays an important role for the reliable, cost-effective and environmentally sound extraction of reserves. Two example cases that employed cold weather drilling technology are the Arctic-class Sunkar barge rig, designed specifically for drilling the North Caspian Sea, and the Yastreb land rig, deployed for drilling Sakhalin-1 offshore targets from a land location.

Sunkar Arctic barge

Kazakhstan's borders span the north Caspian Sea to the eastern mountains adjoining China and Russia. The country produces most of the 1.5 million b/d of oil now flowing out of the Caspian region, with oil reserves estimated between 18 billion and 33 billion bbl. Although most production derives from Karachaganak and Tengiz fields onshore, extensive offshore reserves lie in the Kashagan field with 13 billion bbl estimated reserves.

A shallow draft barge rig was contracted to drill five exporation wells south of Atyrau in the Northern Caspian Sea in the first offshore drilling operation attempted in Kazakhstan. The Sunkar was mobilized through the Volga-Don River Canal System to the Russian port of Astrakhan for final rig-up and assembly (Figure 1). The rig-up was completed in 1999 and towed to its first location. Six years of exploration have been completed in the Kashagan field and reserves in Aktote, Kairan and Kalamkas planned for evaluation.

Delivering the world's only ice-class shallowwater barge was challenged not only by extreme weather conditions but by high-pressure/high-temperature reservoir conditions, sour gas, subsalt structures and a shallow marine environment in which there was no history of offshore drilling.

Environment

The area of operations is a world-renowned nature preserve home to the Caspian seal and many species of waterfowl. The target reservoir is characterized by deep salt formations overlying the target reservoir, high bottomhole pressures, a highly fractured limestone target and 20% in situ hydrogen sulfide (H2S). Seasonal changes impact drilling and supply operations. Sea level changes, a shallow sloping seabed gradient and high wind create hazards for supply vessels. Flowing ice presents a risk to the rig and vessels, requiring a slowdown in drilling capacity from late November until late March. In the winter, temperatures drop to -41°F (-40°C) and the North Caspian freezes to a thickness of 3 ft (1 m) (Figure 2).

Rig design

The basis of design to drill in this unique part of the world centered on several key aspects:

•safety for environment and people;

•remote, shallowwater offshore operation;

•severe weather conditions; and

•high pressure, high temperature and sour gas.

The final design employed a refurbished shallow water swamp barge previously drilling in the Nigerian Delta area. The original scope included upgrading quarters, mud systems and stability systems; however, a detailed analysis of environmental and weather conditions created a revised design complexity. Category specific modifications are listed below.

•Weather

-hull sponsons for storage, draft and stability

-14-ft (4-m) ice deflectors

-sloping hull, low-temperature steel

-6-ft (2-m) diameter piles

-custom icebreaker

•Environmental

-zero discharge

-cuttings auger and conveyance

-processing barge

•Well control

-Living quarters expansion, temporary refuge

-blowout preventer (BOP), choke manifold upgraded to 15,000 psi

-fire, smoke and gas detection system

-Arktos escape vehicles

-TOGA gas diversion

-custom heating, ventilation and air conditioning (HVAC)

•Drilling performance

-three simultaneous 1600-hp mud pumps

-power matched to HVAC, top drive and pumps

-communication system

-Varco TDS3 top drive

-1.3 million lb-ft arctic rated hookload

-self-sufficient storage with ballast tanks, mud pits, drill water tanks, fuel tanks, potable water, base oil for drilling mud and brine.

Unique features and benefits

Four unique systems were deployed for the first time during this project. The Arktos escape vehicle is an amphibious, tracked vehicle with a jet propulsion engine that can be driven on the ice and climb ice rubble in or out of the water. The unit also includes safe breathing air systems. Because of unpredictable water levels precluding reliable use of escape boats or support vessels, these units provide a means to evacuate the rig safely and rapidly.

Rig accomodations and work areas operate at positive pressure. Additionally, alarms function interactively with the HVAC system to seal off areas upon detection of poison gas or smoke. Both features protect personnel and permit time to access the self-contained breathing apparatus (SCBA) prior to work or escape.

The Temporary Refuge is a room designed specifically as a command center and evacuation point. It is equipped with winter survival suits, SCBA and cascade air portals. The unit ensures communication and protection for personnel during drills or emergencies.

Support vessels include an array of Arctic-class icebreakers, tug boats, helicopters and supply barges. Icebreakers have an 800-ton cargo capacity, operate in less than 10 ft (3 m) of water and can navigate through 3-ft (1-m) thick ice.

Yastreb Arctic and seismic class land rig

Russia's second major offshore oil and gas project commenced in Northeast Sakhalin Island targeting the northern flank of the Chayvo offshore oil and gas field with wells drilled from an onshore location. The Sakhalin-1 license area includes three fields discovered by Rosneft-Sakhalinmorneftegaz 28 years ago, with ultimate recovery for all phases of the project expected to exceed 5 billion boe. Second-phase operations will target the Odoptu and Arkutun-Dagi fields.

Drilling continues on Chayvo with well displacements between 4 miles and 6 miles (6 km and 10 km) and vertical depths of 8,530 ft (2,600 m). These extended-reach well trajectories rival worldwide limits of this techology.

Extended-reach drilling (ERD) development not only precludes the cost of an offshore platform installed over the reservoir, but also improves well productivity with horizontal Miocene completions. Moreover, West Pacific Grey Whale migration routes intersect the Chayvo field location offshore, so the land-based surface location avoids any disturbance.

In addition to well engineering specifications, because of environmental concerns, frequent seismic activity, remote logistics and Arctic weather, a customized drilling rig was developed to optimize the project. The Yastreb (Figure 3) was designed, contracted and completed in 18 months with components fabricated across four US states and six countries. Final assembly and commissioning was conducted in New Iberia, La. After commissioning, the rig was disassembled, crated in cargo packages and shipped to the port of Korsakov, consuming more than 1.6 million cf (47,000 cu m) shipped on three separate cargo vessels. From Korsakov, various containers were transported via barge, rail and trucks to the rig location on Chayvo beach.

Rig-up was completed in the summer of 2003 and a cuttings injection well completed. The first ERD well commenced Aug. 8, 2003.

Environment

Weather conditions on Sakhalin Island are influenced by summer typhoon activity and strong northwest winds during winter. Ice forms in late November, creating a weather window for offshore support vessels and marine logistics. Even during open water periods, frequent severe storms impact offshore operations and air logistics (Figure 4).

The island is also subjected to seismic tremors and has experienced major earthquakes. The 7.6 Richter Neftegorsk earthquake in 1995 supports the theory of an independent Okhotsk tectonic plate, encompassing the Sea of Okhotsk. Major events in Sakhalin appear to delineate the plate boundaries, which run from the northeastern part of the island to the southwestern tip.

The region is home to an array of wildlife and indigenous fishing areas. The West Pacific Grey Whale ranges from the Sea Okhotsk to Korea with migratory routes passing over the Chayvo field area.

Logistics have improved with the construction of the Chayvo bay bridge in 2003 where rail and trucking are available for limited weight loads, and the expanded Noglicki airport.

Rig design

The basis of design combined innovative structural design and automation to drill offshore targets from a land location, underneath whale migratory routes and in an area of high seismic activity. Perhaps the most challenging aspect, however, was that the entire project was fast-tracked to meet an accelerated drilling target. Despite the unique features of the rig design, only 1 year was spent from initial design to load-out. Key design components by category are:

•Weather

-fully enclosed rig

-automated pipe barn

-guillotine door

-double-walled, 2-in. insulation to -41ÞF (-40ÞC)

•Environmental

-cuttings reinjection

-rig liners

-skid rail pilings driven into perma-frost

-lightweight mast racking capacity

-mast assist lateral and torsional brace

-50 skid equipment packages

•Drilling performance

-mast capacity of 1.5 million lb-ft

-3,000-hp OIME drawworks

-top drive torque to 94,000 ft-lb

-four 7,500-psi mud pumps for hydraulics

-matched power with six generators

-9,000 bbl mud storage

-pipe barn, drilling train skid

-pipe handling out of critical path

Unique features and benefits

Winterization specification of the rig is to -41°F (-40°C) with fully enclosed mast, substructure, drilling service "train" and pipe barn. In this way, drilling activities were optimized to ensure workers with the safest work area possible.

The heated, enclosed and automated pipe barn measures 130 ft by 134 ft (40 m by 41 m), with 23-ft (7-m) clearance height inside. Stands of drillpipe and casing up to 20-in. diameter and up to 98-ft (30-m) lengths are made up and racked horizontally in the facility. Forklift access via a guillotine door, automated bucking system, Gantry crane and shuttle catwalk all combine to minimize pipe handling by personnel and conduct dual-activity pipe handling and drilling operations.

The unique drilling package includes a mast and mast assist structure to improve torsional stiffness and strength in a windy, seismically active environment. Flared-bottom boxes also distribute loads along skid rails, which are secured by pilings driven into the permafrost. Fully winterized and with full setback load of 450,000 lb-ft, the mast is rated to 70 knot wind velocity.

The Drilling Service Module or "utility train" contains mud circulating equipment, choke manifold, power generation, compressors and water/fuel tanks. To minimize the location area, six modules and 50 equipment skid packages are stacked and mounted on skid rails to move with the rig. The entire rig is therefore skidded from well to well, allowing batch drilling opeations and skidding times averaging 1 to 11/2 hours.

Conclusion

Arctic and cold weather rig technology is well developed as experience and techniques learned in domestic and international locations have been transferred to progressively improved designs. Culminating in projects such as the Sunkar ice barge and the Yastreb land rig, the industry is poised to expand these technologies to the growing exploration pursuits in frontier arctic regions.