Before you can put a mobile offshore drilling unit (MODU) to work, you have to get it to the well site. This can be a complex and expensive operation depending on the type of unit, distance, and conditions. Depending on the drilling contractor's arrangement with the insurance underwriters and third-party surveyor, a surveyor may or may not be required to be present during the move. The surveyor and underwriter are keenly interested in the seaworthiness of the MODU. The degree of preparation is controlled by the category of move.
The growth and evolution of offshore drilling units have gone from an experiment in the 1940s and 1950s with high hopes but unknown outcome to the extremely sophisticated, high-end technology and highly capable units of the 1990s and 2000s. In less than 50 years, the industry progressed from drilling in a few feet of water depth with untested equipment and procedures to the capability of drilling in more than 10,000 ft of water depth with well-conceived and highly complex units. These advances are a testament to the industry and its technical capabilities driven by the vision and courage of its engineers, crews, and management. From an all-American start to its present worldwide, multinational involvement, anyone involved can be proud to be called a "driller." Since the beginning in the mid-1800s until today, the drilling business commercially has been very cyclic. It has been and still is truly a roller-coaster ride, with rigs being built at premium prices in good economic times and ...
Offshore drilling began in 1897, just 38 years after Col. Edwin Drake drilled the first well in 1859. H.L. Williams is credited with drilling a well off a wooden pier in the Santa Barbara Channel in California. He used the pier to support a land rig next to an existing field. By 1921, steel piers were being used in Rincon and Elwood (California) to support land-type drilling rigs. In 1932, a steel-pier island (60 90 ft with a 25-ft air gap) was built ½ mile offshore by a small oil company, Indian Petroleum Corp., to support another onshore-type rig. Although the wells were disappointing and the island was destroyed in 1940 by a storm, it was the forerunner of the steel-jacketed platforms of today. In 1938, a field was discovered offshore Texas.
We must never lose sight of the fact that a mobile offshore drilling unit (MODU's) primary goal is to drill and sometimes complete wells. Often, when concentrating on the marine aspects of the offshore drilling business, we forget this fact. Every well and site have their own requirements and demands, but following are some general comments, not always applicable to every situation, on MODU equipment and capabilities that should be considered when selecting a unit or planning a well. VDL includes any item of weight that is not included in the lightship of the basic vessel. Lightship is the basic weight of the MODU, including all equipment considered permanent.
As the name indicates, this type of rig is located on a fixed structure previously installed at the well location. The structure may be a fixed jacketed platform, spar, tension leg platform (TLP), or gravity structure; whatever it is, the rig sits atop it. Fixed platforms may have as few as 3, or more than 50 well conductors. Generally, the drilling rig is not a permanent part of the fixed structure. However, on some occasions, the unit is left on the platform for future workovers or additional drilling, if removing it is uneconomical.
The jackup-type mobile offshore drilling unit (MODU) has become the premier bottom-founded drilling unit, displacing submersibles and most platform units. The primary advantage of the jackup design is that it offers a steady and relatively motion-free platform in the drilling position and mobilizes relatively quickly and easily. Although they originally were designed to operate in very shallow water, some newer units, such as the "ultra-harsh environment" Maersk MSC C170-150 MC, are huge (Figure 1) and can be operated in 550 ft in the GOM. This type of unit can be commercially competitive only in the North Sea and in very special situations. Figure 1--Maersk's giant jackup (largest in the world) designed for deepwater use (550 ft in the GOM) and harsh North Sea environment.
Submersibles have application in a limited number situations. There are only seven submersibles left in existence, all located in the Gulf of Mexico. The water depth range for submersibles is between 9 and 85 ft, with a lesser depth rating during hurricane season. Despite their narrow water depth range, they still serve an important, although limited, segment of the market. Most jackup rigs cannot operate in less than 18 to 25 ft of water, although a very few can move into as little as 14 ft. of water.
Considering the many complex factors involved in successfully operating a mobile offshore drilling unit, one may ask, "How do I pick the right drilling rig for the job?" The answer is that often there is more than one rig type that technically can do the job. A review of related topics will show many items that must be considered.
Tender Assist Drilling (TADs) units are drilling units constantly challenging the status quo in drilling. By being in a red ocean market, Tender Assisted had to always find its way to evolve to deliver cost efficient drilling and well intervention solution for the operators. They are focussing mainly on two areas of activity: factory drilling of marginal field and Deepwater Drilling, however due to its flexibility, tender assisted is being considered for various other application. Marginal oil and gas reservoir requires drilling efficiency and an optimisation of any associated costs. The drilling package are fit-for-purpose and optimized for rig move and skidding and are generally opperated by experienced crews who developed themselves on this type of unit.
Beebe, Tony (Northern Offshore Drilling Operations Ltd) | Vazquez, Jose H. (3Dent Technology LLC) | Rousseau, Joseph (ABS) | Samuelsson, Lars (ABS) | Cunnion, Pete (Northern Offshore Drilling Operations Ltd) | Coan, Clay (Northern Offshore Drilling Operations Ltd)
The goal is to define conditions under which a GustoMSC CJ46-X100-D jackup rig designed for unrestricted service can be rated for full operational drilling capabilities in areas with a relatively weak soil top layer and a more benign environment. The GustoMSC CJ46-X100-D jackup rig is designed with environmental criteria derived from the southern North Sea and a bearing pressure of 53.5 MT/m