Evolution of Offshore Drilling and Production Technology

Abstract The technology of the offshore oil industry, which evolved slowly during the first half of the 20th century, has virtually exploded during the last 35 years. During this period, the number of offshore mobile drilling units increased from one to 750 today. Exploratory wells have been drilled in up to 7.000 feet of water while shallow core holes have been drilled in the deepest ocean areas of the world. A total of 64,000 offshore wells have been drilled to date; 3,500 wells are now being drilled per year. Production platforms have been installed in water more than 1,000 feet deep. Similar development patterns have emerged in both the capabilities and numbers of offshore crewboats, supply vessels, derrick barges, launch barges, pipe laying barges, diving equipment, subsea vehicles, helicopters and seismic vessels. At this juncture, the offshore industry is poised to conquer the few remaining offshore frontiers-ultradeep water and deep water ice-covered areas. As these frontiers are being conquered continued emphasis is being placed on reducing costs and increasing operating efficiency across the board. OFFSHORE MOBILE DRILLING UNITS Since mid-century when oil and gas exploration moved onto the continental shelves of the world, mobile units quickly became the primary offshore exploration tool. The rapid development of these units has paced the offshore boom. Today we can drill exploratory wells in all ocean areas except those with ultradeep water or certain combinations of ice types and water depths. As the mobile units have evolved, emphasis has been placed on drilling in deeper and deeper water in increasingly harsh wind, wave, current, temperature and ice environments. There has also been a quest for greater mobility, floating stability, drilling stability, variable deck loads, storage capacity and safety. All of this has been carried out within a framework of getting the job done for the lowest cost. As a result, the four types of mobile units which have evolved-submersibles, semi-submersibles, jack-ups and ships/ barges-have followed somewhat similar development patterns. These patterns can best be discussed by decade. Mobile Units - The 1950's The first mobile unit capable of operating in open water [20 feet] was a submersible unit. This rig, which was commissioned in 1948, evolved from the early drilling barges. These barges were first used to drill wells in the bayous and bays of southern Louisiana in 1933. The novel feature of the first mobile unit was two vertically movable, horizontal pontoons that maintained stability while it was moving on and off location. This first mobile unit was quickly followed by a series of about 30 submersible rigs usin9 various types of moving and fixed stability members, streamlined hulls and spud piles to improve overall performance while moving and drilling. A significant feature that emerged during this early period was the so-called "bottle" design, which used large vertical cylindrical members to provide stability during towing and installation. These cylinders were tapered toward the top to minimize wave forces, hence the term "bottle." They made it possible to install the rig on location horizontally without sinking one end first or using movable pontoons. The "bottle rig" was the forerunner of the semi-submersible designs that would appear early in the next decade.