SEISMIC SURVEY SUPERVISION

From July 1977 spanning a decade, Oceanprobe was called upon by large, medium, and small exploration companies to assist in planning and supervision of their offshore and onshore seismic programs.

This work during this period required a great deal of hands-on supervision, often participating in the line-by-line decision-making process. This period was before regular satellite communication links, and our consultants were often isolated from the home office for extended periods of time.

The nature of the seismic survey, particularly the reconnaissance survey that we were mostly involved in, was to prospect an area of an exploration concession for potential hydrocarbons. Seismic surveying involves the introduction of a high-energy acoustic pulse into the earth's crust. This "energy source" comprised of the release of a high pressure air blast into the water, dynamite, electro-mechanical vibrations, a steam injection, exploding propane/oxygen, or other means.

The energy is of such a low frequency that it is able to penetrate the earth's crust to great depths and is reflected and refracted back to the surface. These reflected/refracted sound waves are picked up by an instrument known as geophones (or hydrophones on the water) - extremely sensitive devices used to render the physical sound wave to electromagnetic signatures.

On the seismic ships during the decade Oceanprobe supervised these surveys, a single, long cable was towed behind the surveying ship. These cables were approximately a mile long (2400 meters more or less depending on the technical specifications of the survey). They were filled with hydrophones spaced at precise intervals. Other instrumentation included depth sensors, and attachment points for cable levelers, or "birds".

On a seismic survey, the surveying ship cruises down a pre-programmed survey line, and explodes the "tuned array" of energy source "guns" at specific points along that line - called a "shot point". The array of hydrophones in the cable receive the sonic echoes from the seafloor, convert them to digital data on shipboard computers, which are processed and recorded on magnetic tape.

Sounds easy, doesn't it?

In fact, it is anything but easy. There are precise quality control specifications demanded by the client oil company that must be followed. The "streamer cable" must be towed at a precise depth range. Too deep and the hydrophones lose their frequency response. Too shallow and the signal-to-noise ratio suffers: the phones start picking up the surface noises of the sea which drown out the sound echoing from the seabed. If the streamer is in a bend, the bend point introduces unacceptable noise in the digital record. If currents or tides cause too much of an angle of the streamer relative to the ship's path, the positioning of each hydrophone is not correct. And so on.

Then you have positioning specifications. In those days we did not have GPS (Global Positioning System satellites). Positioning typically was with shore-based radio-navigation systems, each highly susceptible to storms, radio "skip", range problems, and interference. Also the calibration of these navigation systems was highly critical. Other positioning systems used at the time were bottom-tracking doppler sonar, inertial navigation, and a crude form of satellite navigation.

Finally, you had to be very attentive to the onboard computer systems. Even if all the sensors and guns and positioning were excellent, if the recording instrumentation was faulty you would compromise seismic data.

The oil companies turn to seismic experts to accompany the seismic crews as their quality control representative, to supervise all aspects of the survey. This is a demanding, highly technical job, requiring expertise in not only the complexities of seismic surveying, but also in human relations. Seismic crews - also referred to in the industry as "Doodlebuggers" - are a rough lot, spending long months at sea, often in remote areas. A "Doodlebugger" is a very special breed of cat, and a quality control representative or "Birddog" must be able to work closely with the seismic crew in balancing the goals of the seismic company and the client oil company.

Early on, I recognized the need to provide professional consultants. I determined to provide only degreed supervisors with at least a decade of seismic experience. There were very few available personnel who fell under this restrictive category. Our competitors typically hired gun mechanics and junior observers from the seismic companies, selling them as "geophysicists" , and charging bargain basement prices for their "services".

Through this period of unscrupulous competition, Oceanprobe never allowed its standards to drop. I think our clients appreciated this, and they returned to us for other surveys many times over.

The seismic jobs we accomplished over these ten-odd years are too numerous to list, but I have presented here some of the more notable projects that remain vivid in my memory. In future, I will try to add memorable photographs for your enjoyment.

Make no mistake, these projects were Adventure. They took us to the four corners of the world on virtually every major body of ocean on this planet. They were unforgettable and I take great pleasure in sharing them with you: