form deck to facilitate installing buoys on the riser pipe and for riser stripping operations. The design of the substructure provides for a 40- by 40-foot floor within the derrick legs with 18-foot floor extensions beyond the legs on two sides for mounting the drawworks and for handling tools. The substructure will be 16 feet 6 inches high. Preliminary design of the derrick tracking system, derrick-man elevators, derrick, and substructure have been completed. A scale working model has been constructed to demonstrate the problems which are inherent in the pipe handling procedures.

PIPE HANDLING SYSTEM

The pipe handling system will be used to store and deliver casing, drill pipe and drill collars to and from the hole. The major components of the system include a horizontal pipe racker, emergency vertical racking system in the derrick, a drill pipe elevator, a drill pipe spider, casing spiders, power tongs, and spider deck handling equipment. All of the pipe handling equipment will be hydraulically or electrically powered and remotely controlled by automatic and manual opera

tion.

The horizontal pipe racker components include symmetrical storage racks, port and starboard cranes, and a center track conveyor. This racker provides symmetrical storage of 70,000 feet of casing and drill pipe which weighs approximately 2 million pounds. It is designed to provide the selectivity required for handling a tapered drill string.

With the recommendation of a platform type vessel, it appears that it will be practical to modify the design of the pipe rack structure. Dynamic forces due to vessel motions should be less severe and should allow a reduction in weight which will be very desirable from the standpoint of vessel stability.

Feasibility studies of vertical pipe racking systems located below the derrick floor are continuing. Limited vertical racking in the derrick for emergency purposes are incorporated into the design of the derrick structure.

The drill pipe elevator, which is also a special design, will be used to engage, raise, and lower all drill pipe and drill collars when tripping in and out of the hole. The drill pipe spider, which is also a special design, supports the drill string at the derrick floor level during these tripping operations. The power tongs are required for makeup and breakout of the drill pipe and drill collars. Capacity for the drill pipe elevator and spider is 500 tons. Torque capacity of the power tongs is 50,000 foot-pounds.

Detail drawings and specifications for the elevator and spider have been completed. A prototype of the power tongs is now available.

All components of the pipe handling system will be assembled and tested at the mockup site before final installation abroad the vessel.

HOISTING SYSTEM

The hoisting system has been designed to handle a 500-ton load at an average velocity of 125 feet per minute. To fulfill this requirement a 4,000-horsepower drawworks is needed with a 12-part line system for a single line pull of 85,000 pounds requiring a 134-inch-diameter

drill line. The crown block has a capacity of 500 tons and is compatible with a similar capacity special split design traveling block. The hook is a special integral hollow bore design that will permit running wire-line tools while circulating and/or rotating.

ROTATING EQUIPMENT

Two methods of rotating the drill string from the surface will be available; the conventional rotary drilling method which uses the rotary table to deliver torque to the string, and the power sub. The power sub method has decided advantages in a coring operation.

MUD PUMPS

Mud pumps are required for circulating the drilling fluid through the drilling circuit, and for providing energy to the down-hole turbo

corer.

Maximum pump requirements have been estimated at 5,000 pounds per square inch pressure and 550 gallons per minute volume. This is representative of the most severe condition-the drilling of 75-inch hole at 35,000 feet. Data from the turbocorer test program will be available in 2 weeks; verification of the maximum pressure drop calculations will be made. It is believed that the test data will indicate the drilling of most of the Mohole will be at significantly less severe hydraulic demand and possibly within the capacity of existing mud pumps.

A program is scheduled for testing the endurance life of the expendable component parts of plunger pumps under maximum expected conditions of pressure and volume. In addition, this program will determine volumetric and mechanical efficiency and possibly disclose critical conditions such as harmonic vibrations that may result from operating two or more of these pumps in parallel.

DRILLING INSTRUMENTATION

Conventional indicators and recorders for monitoring and evaluating the drilling operation will be modified as required for this unique application. The only drilling instrumentation research and development program contemplated is the turbodrill instrument package which is being developed to register downhole data on surface indicators and recorders. An instrumentation and control system is being developed for the automatic pipe handling equipment. Combination pipe inspection methods will be automated to function with the pipe handling equipment.

HYDRAULIC AND PNEUMATIC POWER

The pneumatic power requirements for the project consist of three basic systems: vessel service air, bulk mud, and cement conveying, and high-pressure buoy inflation.

The four basic hydraulic power systems are rotating equipment power, derrick equipment power, pipe racker power, and the vessel ballast valve control system.

The design of the bulk mud and cement conveying system is complete. Preliminary designs of the other systems have been made.

These power systems service major equipment; therefore, final design will be completed as the major equipment selections and designs are completed.

All pneumatic and all hydraulic systems will be in conformity with ASME and USCG requirements.

In drilling engineering, the critical areas are drill pipe, riser casing and buoy systems, hole reentry systems, and downhole diamond coring equipment.

DRILL PIPE

The Mohole drilling string will be subjected to stress and environmental conditions far more severe than previously encountered in drilling on land or at sea. Nevertheless, years of drilling experience have provided indispensable knowledge which is being applied toward development of the best possible materials, designs, and operating techniques for the Mohole drill string.

The prime contractor has developed conclusive evidence that every practicable means must be adapted to minimize the damaging effects on the drill string of the motions of the floating vessel. These vessel motions impart repetitive fatigue stresses to the drill pipe, and can result in catastrophic pipe failure in a very short time. The most direct and effective step toward solution of this problem is to utilize a drilling vessel which exhibits minimum response to the ocean waves. The damaging stresses which would be imposed on the drilling string by the motions of a conventional ship was a major consideration in the prime contractor's recommendation to drill the Mohole from a column-stabilized platform.

Despite the technological advances made in recent years, there is no reasonable assurance that any material, which would display significant improvement over the best grade of drill pipe now commercially available, can be developed and proved reliable prior to initial Mohole drilling. This conclusion has been reached after extensive and thorough investigation, and has led to the decision to start Mohole drilling operations with a 135,000-pound-per-square-inch yield strength steel which has been successfully used in oil well drilling for over 3 years.

Investigations are continuing on a number of alternate materials with the expectation that one or more of these materials can be developed for drill pipe use prior to the latter stages of Mohole drilling operations, when conditions are most severe. At the present time, the most promising of these alternate materials is a commercial alloy of titanium. The low density and corrosion resistance of this alloy make it attractive, but much remains to be learned about the manufacturing techniques required to produce a serviceable drill string. In the meantime, major effort is being directed toward improving our understanding of the behavior of the steel pipe selected for initial drilling operations. Because of this material's recognized limitations in mechanical properties, it is necessary that design and operating techniques be based on accurate and detailed knowledge of how the material will behave under the expected stresses and environmental conditions.

The testing programs now underway will enable the utilization of two methods for minimizing the chances of drill pipe failure. First, information is being collected on the effects of various types of pipe

defects, and the crack propagation rate. This information will establish the criteria for the development of pipe inspection and equipment and techniques. Frequent and thorough inspection of the drill pipe will be employed to locate and retire from service defective joints of pipe.

To supplement this approach, the testing programs are yielding data on material parameters which can be used in mathematical calculations of the cumulative fatigue damage of any joint of pipe. By monitoring the stresses in the drilling string, it will be possible to calculate at any time how much of the estimated useful service life of any joint of drill pipe has been expended.

THE RISER SYSTEM

The riser system permits a positive means of reentering the hole and returning drilling fluids and bit cuttings to the surface.

A maximum design length of 18,000 feet is specified for the riser. The riser system consists of a landing base, the sea floor connections, the riser pipe, a buoyancy system, and the riser-to-vessel connections.

Six riser systems have been investigated. The presently preferred system incorporates the desirable features of the other systems. This system is preferred because of its simplicity of operation and the accessibility of active components.

This system incorporates the use of a single streamlined variable displacement buoy placed approximately 200 feet below the water surface for pretensioning, makeup and emergency requirements, and passive buoys distributed along the riser for support of the riser deadweight. An investigation is now being conducted to determine the extent of the current drag forces that will be imposed on the riser by these buoys. This design will allow the entire riser to be in tension at all times.

Several preliminary riser stress analyses have been completed. A subcontract for comprehensive stress analysis of the riser system, which will utilize electronic computer facilities, has been initiated. This program will furnish output data for the development and final design of the system. Also, a staff stress analysis program has been initiated and will be conducted in parallel with the subcontracted program for the purposes of analyzing critical areas.

Dual studies are being made on 1034- and 1134-inch outside diameter casing for the riser string. At present it is felt than 1134-inch outside diameter, 54 pounds per foot, grade N-80 casing will produce the most practical riser string. Standard grades of casing, other high-strength steels and alloys are being investigated in conjunction with the drill pipe development.

The buoyancy development program includes selection of passive buoyancy material, design of rigid and variable displacement buoys, development of a charging system and a buoyancy destruction system. The deep water buoys will be subjected to pressures up to 8,000 pounds per square inch. Numerous materials have been investigated for these buoys.

A research and development program to determine the suitability of Pyrex glass balls for deep water buoys is nearing completion. Results to date indicate that these balls will not be suitable.

A program for testing syntactic foam material consisting of glass microbeads in an epoxy matrix for deep water buoys has been initiated. This syntactic foam is presently considered to be the best material available. Limited testing of less expensive material for intermediate depth buoys will also be performed during this test program.

Preliminary designs for the variable displacement and hermetically sealed passive buoys have been made. The final designs will be completed when the final riser system has been selected.

Studies are being made to determine the most feasible method of charging the variable displacement buoys. Compressed air, cryogenic nitrogen, and chemical gas generation are being investigated for charging systems.

Also, studies are being made to determine a system for destroying positive buoyancy in the event of a riser pipe break.

LANDING BASE AND RISER CONNECTIONS

The riser system has progressed to the point where it has become possible to develop a complete group of riser tools to achieve a workable system. It is necessary that these tools be simple and positive in operation and have greater strength than the riser casing in bending, torque, and tension.

The connection of the riser to the vessel requires an adjustable length, load-carrying suspension device. One of the two devices designed is an inline telescoping joint similar to equipment now used in offshore drilling. The other vessel-to-riser connection consists of an array of hydraulic cylinders arranged about the upper riser section. These units are above water and can be satisfactorily serviced when installed on the spider deck of the platform-type vessel. Preliminary engineering designs have been completed on these units.

A special emergency joint has been designed that can be installed in the riser casing at selected points. In the event that any condition causes an excessive angular bend in the riser, this joint will allow clean separation of the riser. This riser angular breakaway joint design could prevent the loss of the drilled well.

A releasible latching tool is required to attach the lower end of the riser pipe to the landing base. Various types of latch tools have been studied. One which is operated by a vertical movement of the pipe has been selected.

All parts work in oil and the magnitude of the latching movement is such that the tool will not be accidentally actuated. A demonstration model and working prototype latch tool are being constructed. It is necessary that casing hangers be incorporated into the system to provide a means of installing protective casing between the landing base and rock. These tools have been designed so that as many as three strings of casing can be installed. A model of these casing hangers and running tool is being constructed. A full-size prototype hanger and running tool also are being built.

Several concepts of the ocean floor landing base have been studied. A preliminary design of a variable buoyancy landing base has been completed which provides the necessary flexibility for use under various bottom conditions. This base is approximately 30 feet outside diameter with a 15-foot-diameter funnel opening and is compatible with the riser-to-base latch and casing hanger system.