Deepwater Production: 1950-2000

Abstract

INTRODUCTION A tension leg platform was just recently installed in the Gulf of Mexico in almost 3000 feet of water. How did the industry get there? Possibly more significantly, how much deeper can we go, and when? I will try to answer the first question by reviewing the history of offshore operations, and I'll then make a stab at answering the other two questions. In addressing the first question, I will focus primarily on technical developments over the past 40+ years in several areas: knowledge of the environment, e.g., oceanography, hydrodynamics, meteorology, and to a less extent, seismicity; analysis; design; soil mechanics/ geotechnology; materials; construction; and instrumentation, testing and calibration. Of course, overshadowing all of these subjects is economics-the bottom line-but my emphasis will be on the technical areas. I will concentrate on steel drilling/production structures in the Gulf of Mexico and Offshore California, fully realizing that concrete structures have played and will play a significant role in deep water, certainly in the North Sea, and quite possibly in the Gulf of Mexico in the future. I have divided the fifty-year period somewhat notionally into five segments: The Beginnings; The Learning Curve; Maturity; Alternatives; The Future. THE BEGINNINGS One of the first offshore drilling operations took place in 1938 in 18 feet of water, about 1-1/2 miles offshore Texas, from a wooden deck platform supported by 100 timber piles, each 65 feet long. A long trestle to shore, supporting railroad tracks, supplied the platform. The first "permanent" steel platform (the timber platform noted above was severely damaged by a 1938 hurricane) was installed in 1947 offshore Louisiana in 20 feet of water. The platform employed six templates and was supported by 267 piles made of 8-inch and 10-inch pipe. The design and construction of such steel platforms were dictated by available sizes of structural members and by existing construction equipment (70-ton crane). Design wave height in 1947 was 32 feet, upped to 40 feet in 1949 when a hurricane hit the Texas Coast. Design wind velocity in 1949 was 125 miles/hour. Wave forces were calculated based upon a chart using solitary wave theory. The forces were less than 1/3 of those which would be used today. Foundation design was based upon a series of seven core tests, some taken to 400 feet, along the eastern Louisiana coast. Pile driveability tests were also conducted to 165 feet of penetration. By 1953, seventy steel platforms had been installed, the deepest in 70 feet of water. In 1955, a platform was installed in 100 feet of water, followed in 1959 by the installation of a 4-pile "minimum" platform in 204 feet of water. Major advances during this period were in the area of installation equipment. A 150-ton derrick barge specifically built for offshore use was available in 1950. By 1953, another barge of 250-ton capacity was in service. Platforms were lifted into place by the crane, not launched. If the platform weighed too much for one crane, two were used.