Notwithstanding the economic, environmental and social challenges, it is widely recognised that a substantial part of the worlds’ undiscovered reserves of oil and gas

may be located in the Arctic.Large areas of the Arctic are currently in the exploration

and appraisal phase, and in this article Kvaerner shares some of its experience in delivering substructures for oil and gas production in subarctic locations, as well as providing a look into the near future for concepts and designs developed for exploration purposes. The content of this article is based on a concept development study for the Northern Shelf

offshore Russia. However, the CONDRILLTM MODU concept has broader application across the Arctic. The concept should be tailored and optimised for actual design conditions.

Large areas of the Arctic’s most promising prospects are in waters that are ice infested for parts of the year or in the path of drifting sea ice or icebergs. The most accessible areas are of relatively shallow water depths and with soil conditions mostly of the unconsolidated type. The industry naturally is looking for units that can access these areas on exploratory missions, preferably as re‑locatable mobile offshore drilling units ‘MODUs’. Due to the extreme environmental conditions and

LEIV WANVIK,

KVÆRNER CONCRETE

SOLUTIONS AS,

MOSCOW, EXAMINES

A MODU CONCEPT

DESIGNED TO ALLOW

OPERATORS TO STAY

WORKING IN THE

ARCTIC ALL YEAR

ROUND.

| Oilfield Technology Reprinted from February 2016

the challenging sea ice and icebergs, current activities have been directed towards areas that are historically accessible with open waters in seasonal windows ranging from three to six months of the year with large variations and low predictability.

Given this background the industry is looking for MODU solutions with capability to stay in position and be in operation year around, including shift of drilling locations on a one to two times a year frequency. Areas of interest are typically Northern hemisphere locations like Sakhalin/Sea of Okhotsk, Kara Sea, Laptev and Chukchi Sea, as well as the Alaskan waters (Beaufort Sea).

Like exploration and appraisal activity elsewhere, the purpose of an Arctic drilling unit is to drill into anticipated hydrocarbon bearing structures and verify discoveries by sampling or well testing. However, the environmental and logistical challenges associated with operations in these areas represent new territory

for human activity as well as technology, especially when considering typical MODU operations.

A need for the drilling of multiple shallow water locations with water depths in the 20 ‑ 60 m range on an all year basis seems to disqualify floating drilling units. Mooring in shallow water cannot offer the capacity to resist ice or ice ridge loading. Jack‑up type units are forced to limit operations to a short summer season as sea ice and ridges may damage legs and/or unprotected conductors/risers.

A robust concrete gravity base type structure (GBS) seems to be the only feasible solution for year‑round drilling provided it can be made relocatable in a rational and effective manner also during winter/ice seasons.

Challenges to be met can be summed up as follows: Ì Collect historical statistics of the environment

including hind casting techniques to develop regional operational design parameters.

Ì Determine and develop understanding of the interaction between structure and ice, globally as well as locally, meeting operational criteria with robustness under a wide range of soil conditions as surveys are almost non‑existent in most of these areas.

Ì Determine and design for winterisation requirements for structures, equipment, operations and human working environment limitations.

Ì Investigate the expected extreme requirements to the MODU’s need for endurance/provisions and storage/spares and repair capacity for long term operation without traditional reliable resupply.

Ì Get access to research and experience available on human behaviour influenced by factors such as remoteness, limited communication, isolation, crew rotation, long haul helicopter flights and regularity.

Ì Understand the new level of HSSE required for humans and equipment for emergency evacuation and contingency plans in the Arctic (life support, stand by vessel, hospital, medical services and supplies).

Ì Design and development will have to take place in an environment with limited availability of suitable or accepted regulations, codes and standards, involving a number of national authorities (governmental as well as regional) that may involve themselves along the project time line, even at late stages.

In a recently performed screening study, Kvaerner concluded that a four column GBS is the best suited MODU concept to handle the above challenges.

Mono‑column designs were looked into but had detrimental setbacks and limited capacity when it came to transient stability, although their performance with in situ ice was favourable. The choice of the four‑column concept combines the efficiency of the stability columns of a semisubmersible with a satisfactory separation of structures in the ice zone to prevent building up of clogged ice and ice floes between the columns.

This MODU concept is a robust concrete GBS based solution stemming from a well proven technology family of Kvaerner GBS’s delivered to the oil industry, with more than 20 platforms worldwide delivered up to this date.

The Kvaerner CONDRILL MODU provides year‑round drilling in ice‑laden waters. The suggested design can accommodate a large range of water depths with safe

Figure 1. Sakahalin ‑ Lunskoy‑A (LUN‑A) GBS delivered by Kvaerner 2005.

Figure 2. CONDRILL MODU In operation.

Reprinted from February 2016 Oilfield Technology |

stability margins under moves, and in situ placement under variable soil conditions thanks to GBS foundation technology. Like the GBS production platforms, the CONDRILL’s stability is secured by skirts, which sink into the seabed, allowing the creation of a formidable suction force in segregated compartments between the concrete base and the seabed. The platform can be refloated by de‑ballasting as well as forcing the platform loose from the ground by pumping water into the same skirt compartments.

The platform can be relocated in most ice conditions – up to 70% ice concentration and 1.5 m (4.9 ft) thickness – using a combination of icebreakers and ice‑class tugs. Relocation can be performed in a matter of days, depending on the distance to the next drill site.

High strength concrete as used in these designs is a good material for the Arctic as it can withstand the harsh environment, including the extreme ice loading and grinding of ice on the legs, whilst requiring virtually no maintenance.

The company’s experience in this field is shown in the delivery of the three concrete gravity base platforms offshore Sakhalin, all constructed and designed to withstand drifting sea ice, temperatures down to ‑44˚C (‑47.2˚F), high seismic exposure and year‑round drilling.

Ice conditions off Russia’s North coast are more demanding than the Eastern coast waters off Sakhalin with thicker ice and the possibility of multi‑year ice in some areas. As a consequence Kvaerner has been carrying out successful test programmes for determining concrete platform resistance to higher ice loads, globally as well as local load scenarios, and assuring that the design can meet the increased loading.

Kvaerner’s experience from the CONDRILL MODU development does also contain a range of other challenging aspects. Keywords in this respect are remoteness and extreme operating conditions, resulting in a significant upgrading of the MODU’s endurance/provisions and storage/repairs capabilities. The operations will have to be sized and equipped for long term operation without re‑supply. Compared to a traditional MODU this will increase the payload requirements for the drilling operations substantially. Winterisation of equipment as well as climate controlled working environments and life support systems will also add weight as the exploration platform drilling activities end up being close to an ‘indoor’ climate in most working zones, including pipe racks (‘pipe barns’).

Kvaerner has been looking towards the Arctic North and East of Russia basins where there has been a need for MODUs that can operate in relatively shallow waters – from 20 to 60 m. Such a water depth capability covers a lot of acreage in this region, stepping not too far off the coast away from shore support centres, in the middle of the large river deposits that are expected to contain hydrocarbons.

The CONDRILL MODU has the same basic design as the above‑mentioned Sakhalin platforms (Figure 4), consisting of four shafts supported by a rectangular base, and built by Kvaerner in the VOSTCO Dry Dock outside the city of Vladivostok in Far East Russia.

The MODU substructure is designed for a topsides load of 20 000 t, well beyond the normal requirement of a mobile drilling rig driven by the increased need for self‑sufficiency and the winterisation of equipment and support systems.

Topsides equipment can be supported on a rectangular deck; however, a column top concentrated arrangement of equipment linked with bridge structures will be more cost‑effective. This offers increased safety by distance, weight saving and a more flexible execution of deck/substructure integration.

Drilling is supported by (and takes place through) one dedicated drilling column/shaft, while the other columns support utilities and the living quarter. Drilling consultants such as RDS and Norwegian drilling contractor Odfjell have contributed to the

Figure 3. CONDRILL MODU – LQ on the near side with Helideck and evacuation means.

Figure 4. Sakhalin 1 GBS in VOSTCO Dry Dock, near Vladivostok. Client: ExxonNeftegas Ltd.; delivered 2012.

Figure 5. Artist’s impression of an early production version CONDRILL concept based on a later installed production module as a single lift on top of reserved shaft areas.

| Oilfield Technology Reprinted from February 2016

drilling design and arrangement that has been subject to several positive reviews.

A consideration in this development has been to make the drilling platform convertible into a production platform. A promising discovery could, if planned for, be brought on‑stream relatively quickly. This has been done with two original drilling platforms now operating in production mode off Sakhalin – Orlan, a steel platform, and Molikpaq, a hybrid concrete/steel structure. Some of the CONDRILL MODU drilling area space and storage capacity could be converted to take production equipment, and the legs could be used for oil storage. The large topside load capacity and spacious deck should facilitate conversion to a production platform capable of handling medium‑size fields. As the MODU turns to stationary duties, with no further planned re‑location, the topside payload for equipment and provisions can be significantly increased (no transient stability requirements that normally limits the deck weight/payload). A reversed procedure is then required when decommissioning the unit.

The CONDRILL can be constructed in several locations worldwide, but for exploration in the North East Russian waters, Kvaerner has based this particular design on construction sites in Russia. One option familiar to the company is to use the Sakhalin platform construction site at VOSTCO Dry Dock on the East coast. After completion of the substructure it may be towed a short route to South Korea or China for Topside installation in one of the offshore yards with relevant fabrication capabilities. One particular study Kvaerner has conducted looked at maximising Russian equipment content. If a Bentec rig design is chosen, the drilling modules can be assembled and rigged up in Russia and transported to Korea as railroad packages and lifted onto the deck at quayside on the top of the GBS drilling column/shaft. Upon deck completion

and commissioning the unit can be towed to the first drilling location, reachable through transport along the ‘Northern Route’ covering the entire Russian Northern coast.

Kvaerner has to date conducted a number of studies for Russia‑based companies. As part of the scope of these studies other concepts have been examined such as steel jack‑ups, steel caisson vessels, existing semisubmersible rigs and drillships/floaters designed for deeper waters. The conclusion of the studies as well as client feedback received suggests that the CONDRILL MODU represents the only credible technical path available today to provide year‑round exploration operations in ice‑infested regions like the North East Russia basins.

Ownership and operation of a drilling rig traditionally fall to a drilling contractor. This will likely not change with the CONDRILL MODU. However, operating in the Arctic region is such a major undertaking that investments in drilling rig, supply chain, shore bases, contingency plans, emergency preparedness for human safety, environment and adherent documentation and verification must be a joint effort between the drilling contractors and oil companies together with international organisations and national governmental/regional authorities.

Kvaerner has a strong belief in this MODU concept based on its reception by stakeholders in the Arctic scene and is continually developing the design with both internal and external funding. The concept is based on mature and current technology, including construction and execution methods and existing facilities.

References1. Magnus Egge, ‘Concrete – The heavy duty solution’, Kvaerner‑ Frontier

Magazine, (Autumn, 2014).2. Arnt Knudsen, ‘Concrete Platform could extend exploration season in

Northern Russia’, Kvaerner ‑ Offshore Magazine, (November, 2014).