Hydrocarbons Under The Sea - A New Survey Technique

Abstract Hydrocarbons seeping from the sea floor can reveal the location of commercially significant offshore-oil and gas deposits. Such seeps produce a localized increase in the concentration of hydrocarbons dissolved in the adjacent sea water, but these concentrations will be transported and dispersed by marine currents and mixing. Calculation of the resulting concentration patterns shows that an optimum search requires sampling very near the sea floor. Equipment to perform such searches has been constructed and tested. A submersible, pump is attached to special faired tubing containing hose and electrical and support cables. An automated winch deploys or recovers the hose and pump at survey speeds. Sampling can extend to depths of 185 meters at speeds up to 6 knots. Sea water from the pumping system is passed through a rotating disk stripper, where over 95% of the dissolved light hydrocarbons are removed by a counter-current flow of purified air. Total hydrocarbon concentration is measured continuously. Ethane, propane, and isobutane are collected, and six-minute integrated samples are determined continually. Sensitivity is sufficient to measure natural levels in the open sea. The system contains integral "blank" and "calibrate" functions and is designed to function automatically without constant operator attention. Seeps Point the Way Oil and gas seeps have helped to guide oil exploration ever since Drake drilled a seep area to the first producing oil well. Link (1952) prepared an extensive review of their types and locations and emphasized that they have provided the first clues to most of the major oil producing regions of the world. He showed that such features are widespread, numerous, and almost always found when there are major deposits. The Texas-Louisiana area is considered anomalously free of large seeps yet Link was able to locate more than 85 oil and gas seeps within 100 miles of the coast in those two states alone. Gas seeps of dramatic strength are well known.