Magazine article Oceanus

Technology Developments in Scientific Ocean Drilling

Magazine article Oceanus

Technology Developments in Scientific Ocean Drilling

Article excerpt

Engineering technology and drilling operations advancements have been preeminent since the Ocean Drilling Program (ODP) began in 1984. Engineering and drilling challenges identified at COSOD I (Conference on Scientific Ocean Drilling) in 1981 and met in the first two years of operation include carbonate reefal sequencing (Bahamas, Leg 101), high-latitude drilling (Baffin Bay, Leg 105), ridge-crest drilling (Mid-Atlantic Ridge, Leg 106), and accretionary prism sequencing (Barbados Transect, Leg 110). In addition to converting an oil/gas industry drillship and outfitting it for scientific coring, the Ocean Drilling Program's Engineering and Operations team began in 1984 to plan for the difficult and wide range of lithologies and conditions to be encountered.

Diamond Coring System (DCS)

Planning how to best drill a hole on an unsedimented ridge crest of the Mid-Atlantic Ridge was ODP's first major technical challenge; known rock-drilling techniques required 50 to 100 meters of sediment for drill-string stabilization before rock could be cored. Completely new systems were required, and industry contracts were awarded for the design and development of:

* a hard-rock guide-base system (including deployment on the seafloor),

* a real-time subsea TV system for reentry operations,

* positive displacement coring motors,

* a cementing system for both guidebase anchoring and hole stabilization, and

* improved roller-cone drill bit design for basement lithologies. While ODP's results from coring unsedimented ridge crests have not been totally successful, they are, however, encouraging. With each successive leg dedicated to either ridge-crest or crystalline rock drilling, ODP has gained better understanding of the problems posed by bare rock and fractured formations. The results from Legs 106, 109, 118, and TABULAR DATA OMITTED 147, together with advice from the mining drilling industry, led ODP to develop a slimhole high-speed coring system, named the Diamond Coring System or "DCS."

The DCS prototype (demonstrated on Leg 124E in 1989, offshore of the Philippines) had a tubing length limited to 2,000 meters, while the DCS currently under development will have 4,500 meters of total tubing length. The DCS encompasses several primary subsystems: a tubing/drill-rod string for offshore deep water slimhole drilling and coring operations; special slimhole (less than 15 centimeters outside diameter) diamond core bits to function in a variety of operating environments; a modified wireline retrievable core barrel, modeled after a mining-style design; an electric top drive, secondary compensation system, mud-pump controls, hydraulic power unit, and other ancillary support functions; and a specially designed, tapered stress joint, for modulating American Petroleum Institute drill-string bending stress at the hard-rock base.

The DCS system is expected to solve several high-priority objectives identified in 1987 by COSOD II working groups, especially for deeper drilling in difficult lithologies. In the last five years the oil and gas industry has begun using slimhole technology and rigs in their exploratory drilling. Because of the technological progress amid environmental and budget constraints in the oil field, slimhole drilling has been pushed to the forefront. …

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