Ten Years Experience in Deepwater Drilling - 1,000 to 5,000 Feet
Authors: Hammett Dillard S 
Published: December 2007

This paper presents the past, present and future of deepwater exploration drilling (600 to 13,000 ft.). Specifically presented are the technical achievements that were necessary to move beyond 600 ft. water depths and to provide the capability to drill in 13,000 ft. of water. Also presented are several examples of these technical achievements which have been experienced by exploration drilling units in the deepwater enviornments during the past 10 years.

Introduction

The Petroleum Industry over the past 100 years has moved from drilling offshore on fixed platforms which extended from the shoreline to floating drilling far offshore in water depths greater than 5,000 ft. The environment offshore, which our industry has confronted and worked in, has been more challenging and rewarding than man's trips to the moon. Offshore drilling has been challenged by water depth, currents, tides, waves, wind, icebergs, pack ice, ice floes and distances. Not all places in the world have any or all of these environments in a hostile condition.

The world's oceans have challenged man's imagination, fortitude and technological capabilities for centuries on end, dating back to the days of Columbus and Magellan and including more recently highly sophisticated operations such as drilling in 5,000 ft. of water or drilling in offshore areas where ice and icebergs are common occurrences at the drill site.

The technology of drilling a hole and the equipment needed to drill a hole have been perfected for inland operations for the past 70 years. This same technology and equipment have for the past 25 years have been extended offshore, first on small platforms, then on barges, jackups, mobile platforms, and floating ships and semi-submersibles.

Examples of hostile environments which the petroleum industry has confronted are illustrated in Figure 1. These include pack ice in the Arctic; moving ice in Cook Inlet, Alaska; icebergs in Greenland; hurricane storm waves of 70 ft. in Ireland; deepwater in 5,000 ft. offshore Canada, currents of 4 knots offshore Thailand; moving ocean floor sediments in South America; tides of 30 ft. offshore Canada, and winds of 100 knots in the North Sea.

The trend in offshore exploration clearly shows that the industry will and can move to deeper water environments to drill and explore for oil and gas (Figure 2). Records show that it took the industry 20 years to move floating drilling from 100 ft. water depths to 1,400 ft., yet in the past 10 years we have extended the water depth an additional 3,600 ft., from 1,400 ft. to 5,000 ft. We have now drilled more than 400 exploration wells in the water depths of 600 ft. to 5,000 ft. The future indicates we will be drilling in over 5,000 ft. water depths next year and 13,000 ft. by the late 1980's.

As water depths increased, floating drilling became necessary. This required three major technological extensions of knowhow and innovation. These include:

In the years 1953 through 1964, the oil industry was developing the technology and equipment to work from floating vessels while drilling exploration wells. All of the above major technological extensions required many hours of engineering, new types of equipment, and years of operating experience to achieve the confidence of the oil industry that exploration from floating drilling was safe and practical. These advances are now routine. Motion. We continue drilling operations in 40 ft. waves and 60 knot winds. Mooring. We have drilled successfully in 5,000 ft. water depths and have stayed on location in 92 ft. waves and 100 knot winds subsea. Safe, remote operations, subsea BOP control, etc., have been routine in the 4,000 wells drilled with subsea equipment offshore.

The past 10 years, 1971 to 1981, have required major technical achievements in deepwater exploration drilling technology. Dynamic stationing with ships like the SEDCO 445 (Figure 3) had just gone into operation in 1971 in 1,400 ft. water depths. The past 10 years, dynamically stationed drill ships similar to the SEDCO 445 have continued to operate without anchor mooring while drilling wells in water depths between 600 to 5,000 ft. Presently our capability is that equipment and technology are available to drill in 8,000 ft. of water (Figure 2).

The achievements necessary to move floating drilling from 600 ft. water depths to 8,000 ft. water depths have been:

Mooring. Development of dynamic stationing to replace mooring systems.

Re-Entry. Development of acoustic/TV re-entry to replace guideline systems. BOP Controls. Development of electro/hydraulic controls to replace hydraulic operations which were too slow. Riser. Development of couplings which can stand high tensions and fatigue equal to pipe body. Development of reliable buoyancy materials to reduce riser tension requirements.

The technology available today gives the industry the capability to drill exploration wells in 8,000 ft. of water. The only limitations to extending this capability to 13,000 ft. water depth are (a) riser handling techniques and (b) formation fracture gradients in deepwater.

Risers can be designed and built to be used in this water depth, but the handling, storing and operating procedures for storm disconnect require additional steps in technology. This step in technology is not great but it does require the incentive of the industry before equipment will be built and procedures established.

Formation fracture gradients in very deep water present a major problem and only setting casing strings at proper depths will solve this problem. Further development of subsea wellheads is required but this is not a problem and can be solved when the need for the equipment is demanded.

The U.S. National Science Foundation is now in Phase I of a program to drill on the Ocean Margin for scientific information. The program will require using subsea well control equipment. The plan is to drill approximately ten wells in water depths of 9,000 to 13,000 ft. Other programs for deepwater are under study in France, Italy, the U.K., Canada, Norway, Germany and Japan.