Important Considerations in Marine Construction

Abstract

Abstract This paper covers some of the problems presented to the oil industry in thedrilling of oil wells in the open waters of the Gulf of Mexico. The hazards, delays and relative costs of offshore drilling are reviewed and various formsof drilling platforms discussed. The requirements of the offshore drilling rig are summarized together withthe principal items affecting the cost of construction. Sea waves and theirsize and characteristics as affecting offshore platforms are reviewed. Drilling platforms are classified as fixed, or fixed and floating. Fixedplatforms of the conventional cofferdam and pile-supported type are discussedtogether with their good points and their limitations. The desirability ispointed out of eliminating as much offshore work as possible where operationsare subjected to constant and expensive delay and substituting therefor theprefabrication of structures ashore or in sheltered waters. Marked economy willcome with the standardization of offshore rigs and special means oftransporting them to the site. Several types of structure which are partly pile-supported and partlybuoyancy-supported are discussed and their possibilities of future usefulnesscommented upon. General Considerations The predominant attribute of offshore drilling equipment is that it must beequal to the job in hand. We therefore give first thought to the matter ofadequacy. In view of the probable depth of drilling, the investment involved and theper diem labor costs, it is assumed heavy modern drilling equipment will beemployed. In order to use such equipment efficiently, the working deck must beample in size and strength and supported so as to be relatively free frommotion and from green seas even in heavy storms. These requirements necessitatea high and rigid land-based support for the drilling rig and machinery withplenty of space for supplies, such as pipe, mud, water and fuel, with reservesfor days when transportation from shore is impracticable. In offshore rigs thecrew will be housed on board in comfortable quarters, probably air conditionedand equipped with a galley and refrigerated food storage. An important consideration will be the ability to transfer stores and crewto and from the rig in all but the heaviest weather and the platforms must beprotected from the impact of supply vessels when alongside. It will beessential to maintain continuous communication with shore by radio or cable, not forgetting the possibility of a helicopter landing space for the transferof crew and light stores as well as a means of general communication. Whateverstructure is constructed must be secure from storms of hurricane force and asafe place for the operating crew to work. If the well comes in, the drillingrig will presumably be removed and a small but rugged pile-supported platformwill remain to carry the Christmas tree with safe working space around it. Itwill be protected from damage on all sides by buffer piles or dolphins. It is assumed that the flowing oil will be piped to storage tanks in thevicinity of the well. T.P. 2324