Drilling Rigs

Early drillships were moored on location using 4 to 8 mooring lines leading to anchors or preset buoys. In 1963, the industry developed a design which permitted the drillship to rotate 360 degrees around an integral turret so it could always head into the seas thus reducing rolling motion.

The evolution of moored drillships follows:

After successful coring offshore California in the 1950’s using spread mooring systems, the National Science Foundation (NSF) needed a stationkeeping system for deeper waters.  In March 1961 the converted 3,400 LT drilling vessel Global Marine CUSS 1 recovered 28 geological cores from 5 holes in 11,700 ft. water depth using manual controlled steerable thrusters.  Although the test was successful it showed that manual thruster control was very difficult.  Concurrently Shell Oil Co. decided to build the 400 LT Eureka with two 200 Hp steerable thrusters with automatic lateral, longitudinal and heading resulting in successfully retrieved cores in up to 3,600 ft water depths in March 1961.  In late 1967 Scripps Institution of Oceanography, sponsored by the NSF and other countries, accepted an offer from Global Marine to construct a 10,000 LT coring vessel (The Glomar Challenger) using digital computers.   The vessel started operation in 1968 and cored throughout the world in up to 23,000 ft of water depth, contributing to the discovery of Global Tectonics.  In 1971, Shell Oil and SEDCO put the newly constructed SEDCO 445 into operation as the first DP drilling vessel which used subsea BOPs and a drilling riser.  This was closely followed by the IHC Holland DP vessel design and the first DP semi SEDCO 709.

These forerunners have led the industry to today’s DP positioned drilling, production, construction and pipe lay barges that can operate in over 10,000 ft. water depths.

Recognizing the pioneering efforts of the following individuals and organizations that contributed to this technology:

Willard Bascom, Bill Bates, Ron Dozier, John Graham, Dillard Hammett, George Lagers,     Howard Shatto, Tom Stockton, Hank Van Calcar, Duke Zinkgraf, Baylor Company (now National Oilwell Varco), CFP (now TOTAL), General Motors, Global Marine (now Transocean), IHC Holland (now GustoMSC), Honeywell (now Nautronix), National Science Foundation, SEDCO (now Transocean) and Shell Oil Co.

The “jackup” concept is basically a hull with multiple legs that can be used to elevate the hull out of the water carrying a drilling rig.  Towed to a drilling location, legs are electrically or hydraulically jacked down to the ocean bottom and then the hull jacked up out of the water.  With the hull out of the water a stable platform exist with wave and current energy acting only on the legs.  The basic concept was developed by Leon B. Delong during World War II for construction platforms and docks.  The first jackup drilling rig was the Offshore Rig 51 (also known as the Delong-McDermott “No. 1) commissioned in 1954.  Thereafter there were many shallow water designs having multiple tubular legs (4-6 ft. diameter to later over 10 ft. diameter) with varying numbers of legs (4 to 12).  Each leg had a donut shaped large “spud can” attached to its bottom to lessen ocean penetration.  As designs matured the number of legs reduced to 4 and eventually to 3.  In 1955, the first 3-legged lattice leg jackup, the Scorpion, was built by the R. G. LeTourneau for Zapata Offshore Co. headed by George H. W. Bush, the future president of the United States.

Through the 1950s and early 1960s there were many designs, owners and builders of jackups featuring different hull shapes and sizes, number of legs, water depth capabilities (most less than 150 ft. with a few up to 300 ft.) and stern slot sizes to fit around existing platforms.  By the mid-1960s the vast majority of designs had settled into two types. First was the “mat” type with 3-cylinder legs attached to a very large mat that rested on the ocean bottom when in the drilling position.  During tow, the unit’s hull, where all the drilling equipment was located, floated with the mat jacked up snuggly next to the hull.  The jacking system usually consisted of pegs (6 or more on each leg) moved in and out of slots on the cylindrical legs. The second type was the “independent” lattice leg, usually 3 or 4 cords, in which the jacking system was done via rack and pinion system located on the outside edge of the cords.

Advantages of the mat rig were its low cost to build, no spud can holds left on the ocean floor, no “preload” to resist storm overturning and it could sit on very soft ocean bottoms.  Their disadvantages included a tendency to slide off location in severe weather, slow towing, a smaller deck load capability, and the mat bottom was subject to damage if it sat on a protrusion.  Independent leg jackups usually could carry larger deck loads, drill in deeper water and withstand more severe weather conditions.  Their chief disadvantage was that they were more expensive to build, left large spud can holes and most had to “preload” (temporary sea water weight) their legs during jacking, which took time and could be dangerous.  A punch through (soil fails and the leg drops) during preload could result in severe leg damage or loss of the rig.

Jackups have to be very careful during ocean moves.  During the tow, severe weather due to roll and pitch might damage legs due to bending stresses.  When trying to jack up or down on location, 5 ft. waves and/or combined seas of 8 ft. are usually the limit for jacking without fear of damaging the legs and hull by pounding them on the ocean floor.

A major advancement occurred in the mid-1970s with the “cantilever” drilling floor that could move out over an existing platform.  Previous jackups had slots in the stern where they could surround a platform thus being able to drill through drilling slots on the platform.  With increased water depths and bigger platforms, the standard slot of 50 ft. width could not surround these platforms.  The solution was to cantilever over the platform.  By the early 1980s, cantilever jackups were the only type jackups being built.

In the 1970s and 1980s the jackup had become the most popular type mobile drilling rig with over 400 built.  Today the jackup continues to be the work horse of the offshore drilling industry in water depths up to 400 ft.  Designs had become more or less standard with LeTourneau, Friede & Goldman, Baker Marine (Singapore), Bethlehem and Levingston being the biggest builders.  In the 1990s, jackups became much larger, could drill in deeper waters and survive much rougher environments.  Maersk Contractors specialized in the “ultra harsh environment” units and in the 2000s built some units with legs 673 ft. long, could drilling in 500 ft. water depth, had hull displacement with variable deck load capacities rivaling some semisubmersibles designs and had very large drilling capacities.

Principle Companies that Contributed:

Bethlehem Steel                                             LeTourneau Inc.

Ray McDermott Co.                                        The Offshore Co.

Zapata Offshore Co. (Diamond Offshore)

Principle Individuals that Contributed:

George H. W. Bush                                        Colonel Lean B. Delong

Charles G. “Mr. Gus” Glassock                     Robert G. Le Tourneau

Ralph Thomas “J. Ray” McDermott           F. Tim Pease

James E. Steele                                               James C. “Jimmy” Storm

Offshore rigs are vessels unlike any the world has ever known. To be able to build these behemoths and make them seaworthy requires unusual vision, determination and ingenuity. A few shipyards rose to the challenge. Alexander Shipyard, of New Orleans, built the first self-contained, mobile offshore drilling unit (MODU), the Breton Rig 20 in 1949, following an idea developed by John T. Hayward.  

Requiring considerable coordination between the shipbuilders and the drilling contractors, various designs were built in yards along the Gulf Coast. However, the work required the shipyards to make considerable modifications to their engineering and construction practices. Only a few were successful. By 1972, six Gulf Coast yards, Alexander and Avondale, of New Orleans, LA; Bethlehem, of Beaumont, TX; Ingalls, in Pascagoula, MS; LeTourneau, of Vicksburg, MS; and Levingston, in Orange, TX, had built a total of 104 MODUs, a remarkable achievement. Bethlehem developed a unique jackup design that includes our own Ocean Star Offshore Drilling Rig & Museum. Letourneau is still producing jackup rigs of its own design today. 

Two Singapore shipyards, Keppel FELS and PPL, started building offshore rigs in the early 70s. Today, they have emerged as modern pioneers, leaders in researching and designing rigs for deeper waters and severe operational environments.

Recognizing the pioneering efforts of the following individuals and companies who contributed to the development of this technology:  

Alexander Shipyard (now Bollinger Gulf Repair), Avondale Shipyard (now Northrup Grumman Ship Systems), Bethlehem Shipyard, Ingalls Shipbuilding (now Northrup Grumman Ship Systems), Keppel Offshore & Marine, LeTourneau Inc. (now LeTourneau Technologies, Inc.), Levingston Shipbuilding Company, PPL Shipyard Pte Ltd.

Deepwater drilling dictates that operations be carried out from a floating vessel. Drillships heave, pitch and yaw with each passing wave, and the industry needed more stable drilling platforms. A semi submersible obtains its buoyancy from ballasted, watertight, pontoons located below the ocean surface and wave action. The operating deck is located above the tops of the passing waves. Structural columns connect the pontoons and operating deck. When the rig moves its location, the pontoons are de-ballasted so that the rig can float on the ocean surface.

In 1961, Shell Oil successfully converted an existing submersible rig into the first semi submersible drilling unit for operation in the Gulf of Mexico. The industry quickly accepted the semi concept and the fleet increased rapidly to 30 units by 1972. At present, there are about 160 semi submersibles in service. First generation semis are generally limited to water depths of less than 600 feet, and second generation are usually intended for water depths up to 1000 feet. Most of these early semis have been retired.

Recognizing the pioneering efforts of the following people and companies who contributed to the development of this technology:

Bruce Collipp, Jerome Goldman, Alden J. “Doc” Laborde, Bill Martinovich, Fred Olsen, Andre Rey-Grange, Aker Mek Verksted, Earl & Wright, a Sedco Company (Transocean Inc.), Friede & Goldman (Friede Goldman Halter), Neptune (Transocean Inc.), ODECO (Diamond Offshore Drilling), Shell

Initial offshore drilling was carried out using small, piled platforms. The equipment, supplies, and personnel were housed on converted LSTs (Landing Ship Tanks) and Y-F (Yard-Fighter) barges, which after 1947, were surplus from World War II. These vessels were known as “tenders” (named after the coal-carrying tenders coupled to steam train engines). R.S. Kerr pioneered the use of tender rigs and is chronicled as the first to strike oil out of sight of land in 1947 in Ship Shoal Block 32. Phillips Petroleum Co. (50%) and Stanolind Oil and Gas Co. (37.5%) were partners in the well. Kerr-McGee acted as driller and operator. The tender was the Frank Phillips. The prototype of the Kerr-McGee tender approach was introduced in Lake Maracaibo, Venezuela, in 1934 and prior to that similar setups had been used in the marshy areas of the Gulf coast. Oil companies bought LSTs and refitted them for offshore purposes after this first discovery. For the next several years, 90% of the offshore wells were drilled from tender-platform combinations.

The narrow gangplank connecting the heaving tender with the stationary platform was called the “widow-maker” with good reason.

Recognizing the pioneering efforts of the following people and companies who contributed to the development of this technology:

Robert S. Kerr, Sr., Frank Phillips Kerr-McGee, Phillips Petroleum, Stanolind (BP)

The industry has applied its considerable ingenuity and determination to protect the environment so that oil and gas wells can be safely constructed offshore. An example of this effort is the development of the Mobile Bay area, offshore Alabama. Zero-discharge means exactly what it says—nothing will be allowed to fall into the sea after it has touched the rig. This includes indigenous rainwater. Also included in the rules are 3 categories of solid discharge—industrial waste, sanitary waste and wellbore cuttings—and 7 categories of liquid discharge. Besides weather runoff, these include cooling water, sanitary water, waste oil, drilling fluids, and machinery deck and mud processing drainage. 

Meeting these exacting requirements were rigs contracted by the developer, ExxonMobil. These included the Rowan 4, Penrod 65 (now Noble Bill Jennings), GlobalSantaFe High Island IV, Penrod Portal 202 (now Noble Joe Alford), Chiles Seabee (now Noble Tom Jobe) and the Penrod Prober 94 (now Ensco 94).  It should be noted that in addition to operating under zero-discharge rules, the rigs had to contend with dangerous hydrogen-sulfide gas, necessitating stringent safety regulations for personnel and equipment. 

The State of Alabama should be justifiably proud of its role in developing the zero-discharge regulations, and the success it has achieved in safely producing hydrocarbons from beneath Mobile Bay. ExxonMobil is to be commended for its role in proving that the petroleum industry can safely drill and produce offshore while protecting the environment. 

Recognizing the pioneering efforts of the following individuals and companies who contributed to the development of this technology: 

The State of Alabama, Chiles Drilling (now Noble Corporation), ExxonMobil, Global Marine (now Transocean), Penrod, Rowan Companies, Transworld Drilling (now Noble Corporation)