Offshore Drilling Units Research Articles

An Investigation into the Loss of the Mobile Offshore Drilling Unit Ocean Ranger

The loss of all 84 persons aboard the mobile offshore drilling unit (MODU) Ocean Ranger on February 15, 1982 and 123 of the 212 persons aboard the MODU Alexander L. Kielland on March 27, 1980 are dramatic examples of MODU accidents. One of the purposes of this paper is to describe the investigative process undertaken by the National Transportation Safety Board (NTSB), the U.S. Coast Guard and the Canadian Royal Commission to determine the cause of the capsizing and sinking of the Ocean Ranger. In that regard, the NTSB analysis and findings are presented. A number of other MODU casualties are summarized in order to put this casualty into perspective. The responsibility for the safe operations of these complex and expensive platforms must be shared among regulators, vessel owners, drilling contractors, operators and labor organizations. The paper examines the national and international rules and regulations that are in place relating to design, construction and operation of MODU's. The NTSB recommendations are put into this shared-responsibility framework.

Foundation Performance of Offshore Jack‐Up Drilling Rigs

An offshore fleet of about 435 mobile jack‐up rigs is currently drilling oil and gas wells around the world. About 2.6% of these jack‐up rigs annually experience an accident which is far greater than any other type of offshore drilling unit. Over one‐third of these accidents are associated with foundation problems. Certain geological conditions pose particular hazards to the foundation performance of mobile jack‐up rigs. To reduce the risk of foundation failure, these hazards can and should be identified by investigating subsurface conditions. Considerable interest is being given to assessing the accuracy of the analytical methods now available to predict the foundation performance of jack‐up drilling rigs. Some commonly used analytical methods are reviewed and actual case histories are presented.

Optimal Preliminary Selection of Mobile Offshore Drilling Units

A comprehensive, systematic method tor selecting a mobile offshore drilling unit is presented. Going beyond the normal, simplistic cost analysis, the procedure includes the unit's performance capabilities and operating time as criteria. The analysis evaluates the suitability of the broad classes of units and/or specific units for the intended operating program. At key points in the analysis subjective decisions are made by the evaluator in keeping with his specific perspective and drilling program needs. Thus the selection utilizes both the quantitative information available on the units and planned drilling program as well as the qualitative decision-making ability of the evaluator. As an example, an evaluation of a general series of units for a multiple-location, multiple-well North Sea drilling program is presented.

Reliability analysis for optimum design

With the widespread increase in industrialisation and the resulting increase in utilisation of World resources an increasing attention to optimum design is forecast. A reliability approach is presented which offers a means of enabling the influence of significant design parameters to be studied and the design to be optimised. It is illustrated by two applications—assessment of ultimate load design procedures for an offshore drilling unit and the derivation of a reliability based inspection procedure for a crop—dusting aircraft. The approach requires extensive data not normally available in design and is still in the development stage, but it is seen as an ideal approach to achieving an optimum design.

Personnel Qualifications for Mobile Offshore Drilling Unit Operations

This paper is based on a study performed to delineate the personnel training and qualification needs for the operations of mobile offshore drilling units (MODUs). These units are used in exploratory drilling for petroleum resources in offshore lands. The study involved a systems task analysis, backed up by a field survey, conducted with government and industry cooperation. A data base was created consisting of structured task descriptions of MODU operations and the skills and knowledge needed to perform each task. The training and experience implications of each task were then considered in relation to the typical MODU personnel organization, personnel sources and characteristics, and the history and trends in personnel selection and training in offshore industry.

Structural Materials for Marine Applications

This paper traces the evolution of ABS hull steels resulting from Important technological developments, service-related problems, and special applications that have led to the diversification of shipbuilding materials. The American Bureau of Shipping has "Rules" and "Guides" for building and classing a wide variety of marine structures. Material applications for such vessels as ultra-large crude carriers (supertankers), offshore drilling units, and liquefied gas carriers are discussed. Because of the Bureau's international activities, specification formulation must take into account adaptability, availability, and cost, in addition to primary technical considerations.

Concerning Wire Ropes for Anchoring Semisubmersibles

If you're about to build yourself a semisubmersible, don't assume that your old Boy Scout Manual will tell you all you need to know about the anchor lines. There's more to the rope tricks than meets the eye, so call on an expert. And call on him early Introduction The expansion of offshore drilling operations during the past few, years has greatly increased our knowledge of anchoring requirements and techniques for offshore drilling units. This experience has been gained under many and varied conditions throughout the world, and particularly in the North Sea, where the severest conditions continue to be encountered. It is true that far more violent conditions are sometimes experienced in other parts of the world, but they are comparatively short-lived; it is the accumulative effect of sustained poor weather that makes the North Sea one of the worst operating areas for offshore units. As a result of earlier experiences with rigs in the North Sea, a new breed of bigger and better rig has been designed and is under construction. Naturally, as the general fabrication increases in size and efficiency, so too must all the component parts. Most of the rigs of this new breed are of the semisubmersible type and therefore mooring members, whether of chain or rope, will obviously play a major role in the total efficiency of the unit play a major role in the total efficiency of the unit and so must be designed with care. Requirements for Good Anchor Lines In the much earlier days of the offshore rig, mooring systems involving wire rope were similar to those used for mooring conventional ships. However, the new sophisticated rigs designed to operate in heavy seas and at greater depths have presented far different problems. It has been necessary to carefully reconsider those designs, fabrication methods, and physical properties. physical properties. Experience has shown that the most important attributes to incorporate into the design of mooring lines for offshore rigs are (1) high strength, (2) high elongation coupled with high elastic limit, (3) corrosion resistance (using maximum effective galvanized coating), and (4) environmental protection (using suitable lubricants and service dressings). The choice of rope for a given application is generally a matter of compromise. In the case of anchor lines, one must also consider resistance to fatigue, abrasion, and deformation. Achieving Strength The strength of a wire rope derives principally from (1) the cross-section of steel area and (2) the tensile strength of the material used. The diameter of anchor line to be used to anchor a given offshore unit will naturally depend upon the size and deign of the unit and upon the forces that will be imposed upon this structure by the wind and the sea. Anchor lines presently being used in the North Sea vary between 2 1/2 and 3 1/2 in. in diameter, and the construction details referred to here are based on this size range. The tensile strength of the material used should always be as high as possible, depending on the construction of the rope employed and the application and work involved, and commensurate with good rope making. JPT P. 659