Instrucciones para la inserción de los datos ATS

Barges are mobile, shallow draft, flat-bottom vessels equipped with a derrick, other necessary drilling equipment and accommodations. Tugboats usually tow them to the location with the derrick lying down. Once on location the lower hull is flooded until it rests on the bottom. The derrick is then raised and drilling operations are conducted with the barge in this position.

Figure 14 A swamp barge.

There are two basic types of barge rigs:

• Conventional

A posted barge is identical to a conventional type except the hull and superstructure are separated by 10 to 14 foot columns, which increases the water depth capabilities of the rig.

Barge workover rigs typically differ from barge drilling rigs both in the size of the hull and the capability of the drilling equipment. Because workover operations require less pulling power and mud system capacity, a smaller, lower capacity unit can be used. In addition, workover rigs, which are equipped with specialized pumps and handling tools, do not require heavy-duty drill pipe. Operating costs for workover rigs are lower because the rigs require smaller crews, use less fuel and require less repair and maintenance.

Because of limited space on the drilling barge, utility barges are positioned alongside the barge rig and are used to:

• Store materials

• A container for cuttings that are dumped from the drilling barge

Barges are built to work in 8 to 20 feet of water. They are used primarily in swampy areas or very shallow coastal areas. They can be found operating in the swamps of river deltas in West Africa and Kalimantan, the US Gulf Coast or in the coastal areas of shallow lakes such as Lake Maracaibo, Venezuela.

6.3.2 Drilling Tender

Drilling tenders are usually non-self-propelled barges or semi-submersibles that are moored alongside a platform. They contain the quarters, mud pits, mud pumps, power generation, and other equipment needed to drill an offshore well. The only equipment on the platform is the derrick equipment consisting of the substructure, drillfloor, derrick and drawworks.

Drilling tenders allow smaller, less costly platforms to be used for development projects. Self-erecting tenders carry their own derrick equipment set and has a crane capable of erecting it on the platform, thereby eliminating the cost associated with a separate derrick barge and related equipment. Older tenders frequently require the assistance of a derrick barge to erect the derrick equipment set.

Figure 15 A drilling tender rig.

6.3.3 Submersible

Submersible rigs are larger than barges and somewhat similar in configuration to the semi-submersible rigs, but the lower hull of the rig rests on the sea floor during drilling operations. A submersible rig is towed to the well site where it is submerged by flooding its lower hull until it rests on the sea floor with the upper hull above the water surface. Pumping out water from the lower hull refloats the rig. Submersible rigs typically operate in water depths of 12 to 85 feet, although some submersible rigs are capable of operating at greater depths.

Figure 16 A submersible rig.

6.3.4 Jack-Up

Jack-ups are mobile self-elevating drilling rigs, equipped with legs and are designed to operate in shallow water, generally less then 350 ft deep (107 m deep). Jack-up rigs are very stable drilling platforms because they rest on the seabed and are not subjected to the heaving motion of the sea. Their barge-like hull may be ship-shaped, triangular, rectangular, or irregularly shaped and is supported on a number of lattice or tubular legs.

The hull of the rig includes the drilling rig, jacking system, crew quarters, loading and unloading facilities, storage areas for bulk and liquid materials, helicopter landing deck and other related equipment. The derrick may be located over a drilling slot indented

Most jack-up rigs have three, four or five legs that are either vertical or slightly tilted for better stability. A few of the earlier jack-ups have eight or ten. The legs may be independent steel feet (“spud cans”) or may have a lower hull (“mat”) attached to the bottom of them. Independent leg rigs are better suited for harder or uneven seabed conditions while mat rigs are better suited for soft bottom conditions.

Figure 17 A jack-up.

Moving a rig from one location to another involves jacking the hull down into the water until it is afloat and then jacking up its legs with the hull floating on the surface of the water. The hull is then towed to the new drilling site by tugs (some jack-ups are self propelled) with the legs raised, projecting only a few feet below the deck. It can only be towed only in good seas and at a slow speed. When the rig reaches its location, electric or hydraulic jacks lower the legs to the ocean floor until a foundation is established to support the drilling platform. The jacking operation continues until the hull is raised out of the water to a level that is above the highest expected waves. The final air gap is usually some 60 feet (18 m) or more above the waves. Drilling operations are then conducted with the hull in its raised position.

There are generally two types of jack up rigs:

• Cantilever jack-up

• Slot type jack-up

A cantilever jack-up allows the drill floor to be extended out from the hull, allowing it to perform drilling or workover operations over pre-existing platforms or structures.

Certain cantilever jack-up rigs have "skid-off" capability, which allows the derrick equipment set to be skidded onto an adjacent platform, thereby increasing the operational capacity of the rig.

Slot type jack-up rigs are configured for the drilling operations to take place through a slot in the hull. These rigs are usually used for exploratory drilling, since their configuration makes them difficult to position over existing platforms or structures.

The chief disadvantage of the jack-up is its vulnerability when being jacked up or relocated. One of their advantages is that they are cheaper than other mobile offshore rigs.

6.3.5 Structure Rigs

These rigs are mounted on production platforms. All the necessary auxiliary equipment is secured on the deck of the platform. The derrick and substructure are capable of skidding to different positions on the platform. After all the wells have been drilled and completed on a platform the rig may be dismantled and removed from the platform.

In some locations, a barge tender supports the drilling activities on the platform. The barge contains the mud pits, pumps, and accommodations. It is connected to the platform by a stairway called the widow maker.

There are five basic designs of fixed platforms:

• Piled steel platforms

• Concrete gravity structures

• Caisson-type monopod structures

• Guyed towers

• Tension leg platforms

Figure 18 Different platform types (from World Oil).

6.3.6 Semi-submersible

Semi-submersible rigs or “semis” are floating drilling rigs that by means of a water ballasting system can be partially submerged so that the pontoons (lower hulls) are below the surface wave action during drilling operations (60-80 feet below the water line). They are supported by a number of vertical stabilizing columns (usually eight) which support an upper deck fitted with a derrick and associated drilling equipment.

The upper deck is attached to the pontoons by large columns. They maintain their position by a series of anchors and mooring lines or by dynamic positioning. Dynamic

Some semi-submersibles are self-propelled; however, most need the assistance of tugs when they are relocated. Some semi-submersible rigs are capable of operating in the "submersible" mode, sitting on the bottom in water depths of approximately 40 to 50 feet (See submersible rigs).

Figure 19 A semisubmersible.

“Semis” differ from each other principally in their displacement, hull configuration, and the number of stabilizing columns. Most types have a rectangular deck. Others may have decks that are cruciform shaped, wedged shaped, pentagonal or triangular. The most usual hull arrangement consists of a pair of parallel rectangular pontoons, that may be blunt or rounded, or individual pontoons or caissons at the foot of each stabilizing column. Both hulls and columns are used for ballasting as well as storing supplies. Pontoons and columns are ballasted to make the center of gravity of the semi-submersible low; therefore, making it very stable.

They can operate in water depths of 20 ft to 2000 ft. Its operational depth is limited by mooring equipment and riser handling problems.

6.3.7 Drillship

A drillship is a self-propelled ship capable of drilling in deep water up to 6000 ft + and offer greater mobility than either jack-up or semi-submersible rigs, but are not as stable when drilling. “Floaters” like the “semis”, they either are anchor-moored or dynamically positioned. Anchor-moored drillships are generally more limited in terms of water depth than dynamically positioned drillships.

The drilling slot on a drillship is through the midsection of the vessel, its center of gravity. It is called a moon pool. The derrick mounted above it gives the drillship its distinctive appearance.

Drillships typically have greater storage capacity than semi-submersible drilling rigs.

This enables them to carry more supplies on board, which makes them better suited for drilling in remote locations. However, drillships are generally limited to calmer water conditions than those in which semi-submersibles can operate, and thus cannot compete as well as semi-submersibles in areas with harsh environments, such as the North Sea.

Figure 20 A drillship.

7 Rig Components