i;2^ 



It is currently thought that present floating drilling techniques can be ex- 

 tended to water depths of at least 1,500 feet (457 meters).* Beyond 1,500 feet, 

 several changes in the existing mobile drilling techniques will be necessary. 

 Three of these changes are described below, and each of them will significantly 

 increase the drilling cost trend. 



1. Dynamic Positioning 



With present marine conductor drilling systems the lateral movements of a 

 floating drilling unit must be kept within 5 or 10 percent of the water depth to 

 permit operations. Most units have eight or more 20,000- to 30,000-lb. anchors. 

 These systems are heavy, costly, and cumbersome, and are not believed to be 

 feasible in open ocean in water depths beyond about 1,000-1,500 feet (305-457 

 meters.^ 



For this reason, dynamic positioning systems have been developed and em- 

 ployed on coring vessels and several ship-shaped drilling vessels. These systems 

 consist of a position indicator, an analog computer, and a propulsion system 

 capable of producing thrusts of a variable direction and magnitude on com- 

 mand from the computer. There are currently four large ship-shape drilling ves- 

 sels under construction which will use dynamic positioning. The largest is the 

 50,000-ton Noess Crusader, whose computer and indicating system alone will 

 cost in excess of one million dollars.^ 



Thus, the capital costs of dynamic positioning systems are high, and because 

 an exploratory well can take 100 days to drill and evaluate, operating and main- 

 tenance costs could be significant. Tliat dynamic positioning is costly is illustrated 

 by the fact that at leaist three of the four drill vessels mentioned above will be 

 equipped with conventional anchor systems for use in most drilling operations.* 



2. Diver Capability 



The deepest working dive on record was to a depth, of 700 feet (213 meters) 

 and consisted of a 15-minute biological survey.^ Laboratory dives have been 

 made to depths slightly greater than 1,000 feet (305 meters),* but it appears as if 

 diver capability will be limited, for the foreseeable future, to less than 1,500 feet 

 (457 meters). While drilling and completion systems have been developed to 

 eliminate the need for divers, it has been found that even vfith these systems 

 divers can be economically utilized to handle unexpected occurrences. The use 

 of submersibles with attached manipulators in depths greater than the limits 

 of diver capability wiU be costly. 



3. Marine Conductor 



The marine conductor extends from the wellhead, which is fixed on the ocean 

 floor, to the floating drilling vessel. This conductor guides the drill pipe and bit 

 down to the underwater wellhead and into the well and provides a return path, 

 for the drilling fluid and cuttings. The guide function insures that as bits wear 

 out and must be replaced the drill string will be able to re-enter the hole ; and the 

 mud returns are desirable to decrease mud costs, aid. in controlling the well, and 

 also give an evaluation of drilling progress. 



Because marine conductors designed to withstand w^ve and current forces in 

 deep water are costly, they are not used in deep water, shallow depth core drill- 

 ing programs. The core hole is drilled until the bit is worn out and the hole is 

 then abandoned. A re-entry drilling system without a marine conductor has not 

 been developed. 



As water depth increases, the cost of a marine conductor also will increase, 

 until at some point a new sysitem for drilling wells may have to be developed. 



B. DEVELOPMENT DRILLING 



1. Platforms 



Generally, when a large field is discovered, a fixed platform is installed so that 

 development w^ells can be drilled with a lower cost platform rig. The platform 

 may also support some production facilities. The exploratory wells are either 

 completed underwater and produced to the platform, or they may be abandoned. 



1 "Humble Gearing Up to Drill in 1300 Feet," Oil and Oas Journal, May 6, 1968. 

 "Ofifshore Report," Oil and Oas Journal, July 10, 1967. 



" J. R. Dozier, "Offshore Oil and Gas Onerations. Present and Future,"' presented at Law 

 of the Sea Institute. University of Rhode Island (.Tune 1966). 



3 "Where Dynamic Positioning Stands Now," Offshore (May 196S). 



* Ibid. 



s Oil and Gas Journal, April 22, 1968. 



« "Men Under Pressure," Ocean Industry (April 1968). 



