SEARCH FOR OIL UNDER THE SEA

Press, Volume XCV, Issue 28262, 27 April 1957, Page 6

SEARCH FOR OIL UNDER THE SEA

Large-Scale Maritime Operations

INITIALLY oil was sought on land, mainly in areas which formerly had been under the sea. Today the search, spreading to the ocean beds themselves, often involves a large-scale maritime operation. Until a few years ago to find these underwater oilfields seemed to be beyond man’s ingenuity. Scientists have shown that the continental shelves off the coastlines of several countries contain layers of likely oil-bearing rocks and these expanses amount to as much as one-twelfth of the entire earth’s surface. But the oil industry is confronted with the necessity to construct suitable platforms which will weather the hazards of unpredictable storms, while providing firm foundations for drilling in water, often over 100 ft deep, down to a mile or more below the ocean bed.

Not all these problems have been solved, particularly in the greater depths of water, but oil is already being recovered in considerable volumes from fields under shallow waters. Experts say that sea drilling is about three times more costly than by rigs erected on land, but the everrising demand for oil has set the pace. The oil industry, with characteristic perserverance, has decided that if oil has to be brought from under the sea, it shall be.

This new technique of offshore drilling comprises two main stages. The first is the preiminary, painstaking, exploration survey by small vessels in the region where drilling is to start This is similar to the procedure employed on land surveys, and its purpose is the same—to give the drillers an indication of where they might be able to strike oil. Skilled geologists, geophysicists and surveyors can chart the positions of likely oil-bearing rocks, but as on land, only drilling can prove whether their deductions have been correct and that oil is contained in the rock strata. Methods of Survey The most-used survey methods are the seismic and gravimetric. The seismic is more costly and complicated but gives the more detailed picture. It consists of making a series of controlled “earthquakes’ which register on instruments to give a contour picture of the rock structure below the sea bed.

A specially-equipped ship, sailing a previously defined course and often following a radar chain to assist in accurate tracking, fires dynamite charges which set up vibrations on the sea bed. These vibrations are picked up by geophones, delicate instruments lying in the water and connected to the ship by cables so that the repercussions from underground strata can be recorded on charts. There are several “earthquake” ships sailing the world’s seas. One of the best-known is the converted Royal Navy corvette, Seislim. This vessel is also fitted with a helicopter landing deck so that the geophone apparatus charts can be flown back to land for swift analysis. The logbook of this ship reflects the range and sweep of the search for underwater oil. In 1956, she was in the South China Sea and in early 1957 she was exploring off the south coast of England. A more laborious, but equally favoured method is the gravity survey. The “gravimeter” measures variations in the attraction of gravity resulting from the distribution underground of rocks with different densities. During the underwater search the instrument is enclosed in a protective casing and lowered from the ship into the water. Its reactions are relayed by remote control to the search vessel. Instruments of this kind have been used extensively in exploration around the Persian Gulf. Test Well Drilled

Rights to explore under are generally acquired by oil companies, as concessions or leases, from governments of the adjoining territories. These may be keenly sought after, as in the Gulf of Mexico, where about three dozen oil companies are operating in an area of some 2,500.000 acres of tidelands up to depths of 250 feet and 60 miles from the shore. Vast expanses may be involved, such as the Bay of Bengal, where a Pakistan oil company has recently acquired exploration rights. Since it has been proved that oil can be raised from under the water, the oil industry is spending millions of pounds on marine exploration. As yet, off-shore drilling is in its infancy compared with land drilling, but the problems are being solved and methods are being improved by practical experience. The outlook for obtaining important and regular supplies of oil from these hitherto inaccessible sources is steadily becoming brighter.

results of the preliminary explorations are promising, the costly and often decisive step of drilling a test well is then taken. For this stage, the industry has introduced a new conception based on great advances in engineering construction and technical knowledge. The culmination has been the development of mobile islands of steel.: floating, monster platforms which provide the base for the heavy drilling derrick and gear, the living space for the crew of 30 men, and helicopter landing decks. Each “island” has been constructed on a basic pattern. It must be able to withstand severe weather and its foundations must support hundreds of tons of materials.. It is often towed as far as 60 miles from the coastline, and its supports are lowered to

the sea floor until its programme/ of exploration is completed, and then the supports are raised and the “island” is towed to another location to resume the search. If oil is discovered, then a means has to be devised of getting it to the shore. In some regions, small, shallow-draught tankers bring the oil from the' well, and,, in others, pipelines are used for this purpose.

Offshore drilling of this ' type was attempted jointly 18 years ago by two American companies, Pure Oil and Superior Oil, but* it was not until 1947 that another American oil group, Kerr-McGee Oil Industries, Inc., drilled thei first producing well ever to be sunk out of sight of land. At’ present the principal areas where these platforms are in use are in the Gulf of Mexico and off the coasts of California and British Borneo. Another platform, after ( an unsuccessful test off Qatar, in the Persian Gulf, was wrecked when a storm sprang up while it' was being moved shortly after Christmas, 1956. This equipment is to be replaced so that exploration in that region can continue.

Recognised Risks The recognised risks which oil companies accept in exploring new areas are intensified when the search is under water. Mobile drilling platforms are expensive. They may cost between £750,000 and -£1,500,000 to construct and £2OOO a day to operate. The accident at Qatar involved a loss of more than £900,000.

These platforms may have to operate in the paths of hurricanes, or among the steamer lanes. Almost every year one or more is lost. In 1953 one company lost a rig when a gas well blew out; fire melted down the derrick and the next day destroyed the platform. In 1949 two landing craft and an entire Shell rig were swallowed in a vast crater created by high pressure gas. The crew on a platform may have to live on board for several weeks without coming ashore. This means that food and other supplies have to be brought to them by helicopters or small ships. In Borneo a novel method of communication with the shore has been provided by the erection of a cable railway, which, however, is only practicable for short hauls.