structure. Knowledge of the precise velocity, direction and timing of currents is needed to position the riser and the ship during operations. With such information in hand, in real time, operations may be planned with greater certainty of success, or alternatively postponed to a time when currents will be slack. Long range, low frequency acoustic Doppler current profilers (ADCPs), such as those manufactured by Teledyne RDI are being utilized in ever more configurations to provide this information, as are single point deep current meters provided by Aanderra Instruments, Nortek, and others. New entries into this evolving field include acoustic instrument manufacturers such as Link Quest. Underwater acoustic communications between different elements, and echo-ranging to determine distances to objects, are key technologies for knowing where everything is under water so that a remotely operated vehicle (ROV), for instance can be directed to attach a bolt, untangle a cable, turn a valve or some other fine motorskill task at depth. Operation of an ROV is controlled from the surface, with the work area being viewed easily via live video. Subsea7, an ROV operations company, equips vehicles with complex feedback mechanisms that tell the human pilot on the surface what they are up against when visibility is limited. At depth, the range of effective vision is typically limited to less than 100 ft., so once an ROV gets beyond that distance from a fixed structure, acoustic technology is necessary for the ROV pilots to know where it is. Improved control systems, video, communications, manipulators, navigation are all being advanced to make ROVs incredibly reliable tools for offshore oil work. Increasingly these "smart" instruments and tools guide the heavy operations on the seabed. All parts of the operation have blossomed. Bigger survey and drilling ships are being built because they have to stay in remote locations for many months at a time; they need to carry more riser pipe; and support longer and more precise deployments. They have to carry huge tanks of expensive drilling mud, tons of cement, huge winches that carry miles of power and communication cables; and they must have deck space for ROVs and their companion control rooms that are the size of tractor trailers. Today's super-drillships, such as Discoverer Spirit and Discoverer Deep Seas, are in the 800-900 foot range. There are three more being built in South Korea for Houston based Transocean, which are expected to come on line in 2010. Each of them will cost over $600 million. All this adds up to huge budgets for oil companies, 42 MTR which motivate them to scrutinize their prospects down to the penny and to the centimeter. For that reason oil companies survey, sample, analyze, resample, model, and calculate again before they spend the money to go into production. The entire process can take up to 10 years and billions of dollars to complete, for a single oil field. That is why oil companies and their many partners invest in or develop the most advanced technologies available to cut the risk of drilling dry holes. A new prospect is first surveyed by seismic survey boats that tow up to nine cables behind them, stretching as much as 30,000 ft. These towed arrays are instrumented with acoustic transducers that record the return of sound reflected from rock layers deep beneath the seabed. The position of each of these receivers must be precisely known relative to the seafloor. This is accomplished by a combination of GPS and acoustic navigation technologies, and the data is assimilated aboard the ship in powerful computers. Because of improved computer speed and digital storage capabilities, data storage that used to take up the entire hold of a ship in the form of data tapes now can be stored in small disk arrays and can be telemetered to shore in near real time via satellite communications links for immediate analysis. Promising geological structures can be identified within days and survey plans can be altered to take advantage of this information. When a survey ship costs upwards of $150,000/day, cutting time to obtain data is very important. Once a spot is deemed drillable, an exploratory drill rig or drillship is brought to the site, and a heavy wellhead structure is deployed on the bottom at the exact location of interest. Then a riser is deployed between the drill rig and the seabed, and mated to the wellhead structure, guided by acoustic pingers and ROV's that nudge it into position. This involves a series of complex maneuvers. Then the drill string is run down through the riser and into casing which is cemented into the sediment and rock. The casing, which is basically a steel conduit which telescopes to smaller diameter the deeper it goes, stabilizes the sides of the well hole in the upper part of the sediments. Drilling mud is pumped through the drill string and drill bit to provide lubrication and ultimately to provide positive pressure within the hole to prevent a potential blowout. Computer aided directional drilling capabilities greatly increase the reach of production wells from a single platform. This technology also helps to decrease the incidence of blow-outs because the drillers have more ability to avoid shallow gas pockets and other dangerous regions. April 2007
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