FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
Method of refurbishing a jack-up rig
APPLICANTS
Larsen & Toubro Limited, Floating Systems Business Unit, Engineering and Construction Division, Powai Campus (W), Saki Vihar Road, Mumbai 400 072, Maharashtra, India, an Indian company
INVENTORS
Kasturirangan Narayanan, Varghese George and Pal Chirag, all of of Larsen & Toubro Limited, Floating Systems Business Unit, Engineering and Construction Division, Powai Campus (W), Saki Vihar Road, Mumbai 400 072, Maharashtra, India, all Indian nationals
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed:

FIELD OF THE INVENTION
This invention relates to a method of refurbishing a jack-up rig.
BACKGROUND OF THE INVENTION
Jack-up rigs are a type of mobile platforms or offshore structures that are mainly used for offshore drilling of oil wells, A jack-up rig essentially comprises a hull, legs with footings (spud cans) and equipments and is designed to stand still on the sea floor, resting on the legs. The most popular jack-up rig design comprises 3 legs, but there are also jack-up rigs with 4 or more legs. Jack-up rigs are generally placed in relatively shallow waters, usually less than 400 feet (120 m) of water. The equipments mainly comprise three types namely marine equipment, mission equipment and elevation equipment (lifting mechanism). After the jack-up rig is towed to a site, the lifting mechanism allows to lower the legs into the seabed and raise the hull to provide a stable work deck capable of withstanding the environmental loads.
The hull is a watertight structure that supports or houses the equipments and accommodates personnel and their belongings and food articles, thus enabling the jack-up rig to perform its tasks. When the jack-up rig is afloat, the hull provides buoyancy and supports the weight of the legs and footings, equipments, and the other loads on the hull. The legs and footings of a jack-up rig are steel structures that support the hull when the rig is in the elevated mode and provide stability to resist lateral loads. Footings help to increase the soil bearing area thereby reducing required soil strength.

A jack-up rig operates in three main modes namely transit mode when moving from one location to another, elevated mode when raised on its legs, and jack up or down mode when the rig is between afloat and elevated modes. Each of these modes has specific precautions and requirements to be followed to ensure smooth operations of the jack-up rig. A jack-up rig can be motorised or self propelled.
Like any other machine, a jack-up rig also requires periodic repairs or refurbishment and maintenance. Dry docks (drydocks) are massive constructions used for the building, maintenance and repair of water crafts like ships, boats or jack-up rigs. A drydock is a huge permanent structure mainly comprising a basin or vessel that can be flooded to allow a water craft to be repaired or refurbished to be floated in and then drained to allow the water craft to come to rest on a dry platform. A typical drydock, popularly known as graving dock, is usually made of earthen berms and concrete and is closed by gates. More routine use of drydocks is for the cleaning (removal of barnacles and rust) and re-painting of ship's hulls.
A graving dock requires huge capital investment to build it and high maintenance cost. Therefore, continuous use of the dry dock is required to recover the initial investments made. This necessitates continuous rotation of the jobs in the dry dock which means a large and constant concentration of labour to speed up activities inside the dry dock. As a result, in order to economize refurbishment of a jack-up rig in a drydock, usually only those areas of the jack-up rig which are inaccessible or difficult to access, such as footings of legs or submerged portions of legs and hull bottom, are refurbished inside a dry dock. The jack-up rig is then floated out of the drydock, parked beside a jetty and jacked up to perform rest of the refurbishment.

This is not only inconvenient to carry out but also increases the labour, cost and time of refurbishment.
Cofferdams are also used to repair jack-up rigs. Cofferdams are sealed externally to the hull of a ship or submarine using pressure differential at or below the waterline in order to dewater an area or system and access the ship or enable to shipboard or to allow divers to conduct maintenance or repairs to the hull or system. Cofferdams are mostly used for maintenance purpose, where a small modification or repair is to be done. Cofferdam approach is effective when the jack-up rig has either no lower leg section (leg section near the spud can) to repair or has spud cans that can pass through the legwells completely.
In the case of jack-up rigs with speed cans that cannot pass through the legwells completely, it becomes necessary to increase the height of the cofferdams to accommodate the speed cans. This will increase the cost of the cofferdams and may also affect the stability of the jack-up rigs. Cofferdams are to be individually designed for various types of legwells and refurbishment requirements. In order to use cofferdams for repair, the rigs are to be in floating condition and the repair activities are to be scheduled in advance so that all major equipment installations happen after jack-up. Cofferdam approach also requires special seals for sealing the cofferdams to the hulls against very high hydrostatic pressures. Cofferdams design also may have to be modified for rigs in particular depending on hull undulations.

Jack-up rigs also can be refurbished by loading in or reverse launching them on top of a jetty using normally a barge or skidway in conjunction with a push-pull mechanism which may be internal or external. Examples of arrangements used for loading in or reverse launching include semi-submersible barge with self propelled modular transporters (SPMTs), semi-submersible barge with beams (greased for skidding) and winches, semi-submersible barge with beams, multi ton rollers and winches, semi-submersible barge with air gas bags and winches, slim barge with self propelled modular transporters (SPMTs), slim barge with beams (greased for skidding) and winches, slim barge with beams, multi ton rollers and winches, slim barge with air gas bags and winches, skidways with beams (greased for skidding) and winches, skidways with beams, multi ton rollers and winches or skidways with air gas bags and winches. The above arrangements are prohibitively expensive. Further the loading and unloading of the rigs on the jetty is also quite cumbersome and time consuming to carry out besides being costly and requiring extensive labour.
SUMMARY OF THE INVENTION
According to the invention there is provided a method for refurbishing a jack-up rig
comprising the steps of:
(i) identifying a refurbishment site having earth of the required load bearing
capacity in the proximity of a sea;
(ii) dredging the site below the level of the sea bed to form a recessed area
having a mouth opening into the sea and having a size corresponding to the
hull of the jack-up rig that would submerge in the water in the recessed area

with a clearance between the bottom of the hull and bottom of the recessed
area;
(iii) forming a plurality of spaced apart reinforced open trenches at the site
corresponding to the legs of the jack-up rig;
(iv) floating in the jack-up rig to be refurbished into the recessed area with
the legs thereof raised up, positioning the jack-up rig in the recessed area,
lowering the legs into the respective trenches and anchoring the legs in the
respective trenches;
(v) raising the hull on the legs, holding the hull in the raised position and
filling the recessed area with earth to the original surface level of the site;
(vi) placing support stools on the earth filled surface area at the site below
the hull and lowering and supporting the hull on the stools;
(vii) repairing the hull and if required, the legs by raising the legs;
(viii) if raised, lowering the legs in the trenches and positioning and anchoring
the legs in the trenches;
(ix) lifting the hull on.the legs, removing the stools and re-dredging the filled
surface area at the site to form a cavity of the required size to allow water to
flow in and submerge the hull with a clearance between the bottom of the hull
and the bottom of the cavity; and
(x) floating out the jack-up rig into the sea after raising the legs.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO DRAWINGS
Figs 1 to 8 of the accompanying drawings illustrate the various steps of the method of the invention schematically. As illustrated in Fig 1, a refurbishment site 1 having earth of the required load bearing capacity is identified in the proximity of a sea (not shown). Instead of sea, the refurbishment site also can be in the proximity of a river or creek (not shown) opening into the sea. Therefore, reference to the term sea in this specification should be understood to include a river or creek communicating with the sea. The refurbishment site is dredged below the level of the sea bed la to form a recessed area 2 having a mouth (not shown) opening into the sea and having a size corresponding to the hull of the jack-up rig that would submerge in the water in the recessed area with a clearance between the bottom of the hull and bottom of the recessed area. The submerged portion of the hull is generally understood to be the draft in the technical field of the invention. In case the site selected for repair contains impediments such as rocks, the impediments are to be obviously removed before dredging. A plurality of spaced apart reinforced open trenches 3 are dug at the site corresponding to the legs 7 of the jack-up rig 5 to be refurbished. The footings or spud cans of the legs are marked 8. (Fig 2). Preferably the reinforced trenches are formed by driving open caissons 4 at the site and excavating the earth from within the open caissons and retaining the caissons in place in the open position.
The jack-up rig is floated in into the recessed area with the legs thereof raised up. The jack-up rig is positioned in the recessed area and the legs are lowered into the respective trenches and anchored in the respective trenches (Figs 3 and 4). The hull 6

of the jack-up rig is raised on the legs and held in the raised position. The recessed area is filled with earth to the original surface level of the site. Support stools 9 are placed on the earth filled surface area at the site below the hull. The hull is lowered and supported on the stools (Figs 5 and 6).
The hull is repaired and if required the legs are also repaired after raising the legs. If raised, the legs are lowered in the trenches and positioned and anchored in the trenches. The hull is lifted on the legs, the stools are removed and the filled surface area is redredged at the site to form a cavity 2a of the required size to allow water to flow in and submerge the hull with a clearance between the bottom of the hull and the bottom of the cavity. The jack-up rig is floated out into the sea after raising the legs (Figs 7 and 8).
According to the invention permanent massive constructions like drydocks, cofferdams with limited scope for repair and expensive arrangements such as semi-submersible barge in combination with mechanisms like skid beams, air-gas bags or rollers have been eliminated. All that is required to carry out refurbishment is that a refurbishment site close to the sea has to be identified, dredged to the required size and reinforced trenches are to be formed. The rig to be refurbished is floated in for repair and floated out after repair after redredging the site. It does not require any permanent structures and expensive equipments. It can be used for repair of hull and/or legs. Thus, the method of the invention is simple and easy to carry out and is very cost effective. It also reduces refurbishment time and increases the scope of repair as both hull and legs can be repaired at the same location.

It should be understood and appreciated that the scope of the invention need not necessarily be confined to refurbishment of jack-up rigs. The invention can be advantageously used for refurbishment of any floating structure or system with legs. Such a variation of the invention is obvious to a person skilled in the art and should be construed and understood to be within the scope of the invention.

We claim
1. A method of refurbishing a jack-up rig comprising the steps of:
(i) identifying a refurbishment site having earth of the required load bearing
capacity in the proximity of a sea;
(ii) dredging the site below the level of the sea bed to form a recessed area
having a mouth opening into the sea and having a size corresponding to the
hull of the jack-up rig that would submerge in the water in the recessed area
with a clearance between the bottom of the hull and bottom of the recessed
area;
(iii) forming a plurality of spaced apart reinforced open trenches at the site
corresponding to the legs of the jack-up rig;
(iv) floating in the jack-up rig to be refurbished into the recessed area with
the legs thereof raised up, positioning the jack-up rig in the recessed area.
lowering the legs into the respective trenches and anchoring the legs in the
respective trenches;
(v) raising the hull on the legs, holding the hull in the raised position and
filling the recessed area with earth to the original surface level of the site;
(vi) placing support stools on the earth filled surface area at the site below
the hull and lowering and supporting the hull on the stools;
(vii) repairing the hull and if required, the legs by raising the legs;
(viii) if raised, lowering the legs in the trenches and positioning and anchoring
the legs in the trenches;
(ix) lifting the hull on the legs, removing the stools and re-dredging the filled
surface area at the site to form a cavity of the required size to allow water to

flow in and submerge the hull with a clearance between the bottom of the hull
and the bottom of the cavity; and
(x) floating out the jack-up rig into the sea after raising the legs.
2. The method as claimed in claim 1, wherein the reinforced open trenches are formed by driving open caissons at the site and excavating the earth from within the open caissons and retaining the caissons in place in the open position.