Drilling From Floating Vessels Now Economically Carried Out Off California Coast
- W.W. Rand (Submarex Corp.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- September 1959
- Document Type
- Journal Paper
- 35 - 36
- 1959. Original copyright American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Copyright has expired.
- 2.4.3 Sand/Solids Control, 4.1.5 Processing Equipment, 4.5 Offshore Facilities and Subsea Systems, 1.10 Drilling Equipment, 1.6 Drilling Operations, 1.10.4 Onshore Drilling Units, 1.6.9 Coring, Fishing, 4.1.2 Separation and Treating
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Deep water occurs at short distances off the California coast, restricting the economic use of artificial islands and bottom-based platforms to a narrow coastal strip. Beginning in 1950, drilling from floating vessels has proved to be feasible and economically sound, and operators are now seeking methods of drilling oil wells from vessels. Significance of results so far achieved has made little impression on the industry, but extension of techniques now in use forecasts widespread use of floating drill rigs.
Search for California Tidelands Oil Began in 1945
Marine seismic methods were first used off the California coast in 1945, inaugurating the tidelands oil search program. In 1946 submarine coring began, with a simple weighted core tube, for sampling pre-recent formations efposed on the sea floor.
In order to take cores from formations buried by overburden, a jet tube and punch core device operable through the jet tube was developed. Early forms required a diver to guide the core tube into the jet tube after the hole had been jetted through overburden by high pressure sea water. Later improvements permitted dispensing with divers. In the fall of 1948, a converted minesweeper was equipped with a 1,000-lb dart, handled mechanically in a tilting cradle mounted overside. This was the first vessel to be outfitted specifically for submarine coring. Although experiments were performed on many types of jetting devices, it was found that a simple jet tool with projecting core barrel provided an accurate and fool-proof method of taking oriented and unoriented cores in areas where the subsea formation was buried under as much as 200 to 250 ft of overburden. Attempts to extend the range of the jetting method resulted in reaching depths up to 500 ft beneath the sea floor; however, at this depth the method is not commercially feasible.
As the need for deeper geological information became urgent, rotary drilling was introduced to offshore exploratory work in 1950. The first rotary unit utilized a seismic drill-type electrically driven rotary table mounted overside in a carriage having a fore and aft axis to compensate for roll of the vessel. In 1953 this unit was removed and replaced with a rotary having a double jack-knife mast with draw-works and rotary table patterned after conventional truck-mounted land rigs. By 1955 drilling vessels were being outfitted which permitted drilling through a caisson located near the center of the ship. These vessels were designed for drilling to about 7,500 ft and at least one ex-Navy barge has been modified to permit drilling to depths of about 10,000 ft (see Table 1).
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