Review of Procedures After Four Years Experience in Floating Drilling

Abstract

Abstract Late in Jan., 1962, Shell Oil Co. began floating drilling operations off the coast of Louisiana in 293 ft of water with the converted floating rig Bluewater No. 1 and a Shell-developed remotely controlled underwater drilling system. A description of current equipment and procedures is presented which has evolved from experience gained in drilling 55 wells from three floating rigs in from 125 to 430 ft of water. Data on these wells are presented in regard to the remotely controlled underwater equipment, various phases of the operation, procedure floating rig performance and economics. The article concludes that the present underwater equipment and a semisubmersible drilling platform are capable of economically evaluating locations in 600 ft of water. Introduction As early as 1955 the need to explore and develop hydrocarbon accumulations underlying water at depths greater than 150 ft focused attention on the required development of new deep water techniques. Studies were made of possible solutions to drilling and completing offshore wells to establish an all-inclusive definition of this complicated problem. At the beginning of these studies it was determined that the technique to be developed must be economical, reliable, safe, flexible and not restricted by water depth or geographical environment encountered on the continental shelves around the world. Techniques considered were drilling and completing wellson a bottom-supported structure with the wellhead above water,with the wellhead submerged below the normal draft of shipping on a structure, or freestanding pile permitting the use of divers during completion andon the ocean floor using either a caisson technique for gaining entry to the wellhead at atmospheric pressures, or an entirely remote system not requiring divers or visual observation. After defining and analyzing the relative merits of these techniques the remote system was found to offer the most feasible solution. Based on this, development of the remote universal drilling and completion system (RUDAC system) was initiated. The successful development and testing of this system subsequently resulted in the conversion of the Bluewater No. 1 from a bottom-supported to a floating drilling rig. Although an optimum design of a floating rig had been completed at Shell Development Co., the use of a contract rig was considered as an alternative. Because of the time element involved in early exploration of new leases in water depths beyond the operational limits of conventional bottom-supported rigs, it was decided to use an existing rig. The Bluewater No. 1 was chosen for its favorable floating characteristics and the rig's adaptability to handle the RUDAC equipment. A mooring system was developed based on drilling under average Gulf Coast weather conditions and evacuation during hurricanes. Modifications and additions to the rig were required to accommodate the mooring system, increase seaworthiness and facilitate trimming, comply with Coast Guard and ABS regulations and handle the RUDAC equipment. Conversion of the rig from bottom-supported to a semi-submersible barge took 44 days. In mid-January, 1962, the rig and the RUDAC equipment were ready to start the deep water exploration program. This culminated 4 years of intensive preparations by Shell Development's E and P Research Div. and Shell Oil's New Orleans Area. Since that time, 55 wells have been drilled to depths up to 15,000 ft in water depths from 125 to 430 ft, at times under extreme weather conditions. Shell's deep water exploration operations on the Continental Shelf of the Gulf Coast are no longer experimental and are now being handled in a routine manner. This is attributable to the thorough preparation of the equipment through extensive testing and improvements made from operational experience. Drilling times are now comparable with those experienced by conventional drilling. This article describes the current system handling, performance and improvements in on-bottom equipment and technique, evaluation and comparison of the different rigs and over-all economics of evaluating deep water prospects, JPT P. 167ˆ