March 1999 Vol. 220 No. 3  Exploration

Perry A. Fischer,  Engineering Editor

Satellites, sniffers, tubeworms and a big footprint

Although they may not indicate a commercial accumulation, hydrocarbon seeps are well-known good omens in exploration. A novel approach at locating them is being tried by Petrobras. Using the Radarsat-1 satellite equipped with a microwave sensor, smooth, non-transient areas on the ocean surface are identified for further assessment.

The technology was developed about 20 years ago, but its primary use was for detecting slicks associated with man-made pollution. New methodology, developed by the Center of Excellence in Geochemistry at Cenpes, was successfully used offshore at the mouth of the Amazon River a year ago. About $1.5 million has been invested in developing the technology.

The Center of Excellence has begun a multi-client data-collection project in the Campos, Santos and Esprito Santo basins, in areas between 300 and 10,000 ft deep. Further assessment of satellite-identified areas involves collecting seafloor samples, geochemical analysis and integration of seismic data. According to Marcio Mello, head of the Center of Excellence, "With this new method, we could add value ... the ideal is to integrate geophysics, geology and geochemistry. These three tools together are the recipe for increasing the success rate and reducing exploration risks."

Portable sniffer. The Australian Geological Survey Organization (AGSO) has had to find another way to carry out its marine geochemical analysis. A continuous geochemical tracer system — commonly called a ‘sniffer’ — was onboard the RV Rig Seismic when AGSO relinquished its charter last June, so the organization decided to invent a portable unit.

Now housed in a shipping container, the new sniffer can be readily transported to, and deployed behind, a wide range of vessels. Dubbed the Mark-2, the new system incorporates a fish equipped with a submersible pump that delivers water to a gas stripper from depths to 200 m (650 ft). The stripper removes dissolved gas for chromatographic analysis every minute. Instruments in the fish telemeter seafloor depth, pH, electrical conductivity, dissolved oxygen and turbidity to the data acquisition module. GPS data is also recorded.

Last October, the new system was tested offshore Australia in a 1,000-km sniffer survey of the Canning basin and a 3,000-km survey of the Yampi Shelf/southern Timor Sea area. Moderately intense, episodic, hydrocarbon seeps were detected and mapped. The sniffer data is currently being integrated with synthetic-aperture radar and seismic data to provide a better understanding of geological concepts relating to seeps, hydrocarbon migration and trap integrity.

Follow those tubeworms. In December 1998, the U.S. Minerals Management Service (MMS) released Stability and Change in Gulf of Mexico Chemosynthetic Communities, Interim Report. This publication provides scientific results from an MMS-funded survey of known natural hydrocarbon seep sites that support chemosynthetic communities in the northern GOM. These weird, non-photosynthetic life forms were first discovered more than 20 years ago in Pacific Ocean hydrothermal vents; they have been studied for more than a decade along the GOM continental slope.

An interesting article in the AAPG Explorer reports on a new study that used digital, long-range, side-scan sonar to acquire 930 mi² of seafloor data. Geophysical surveying for the MMS study was conducted by William Sager of Texas A&M’s Department of Oceanography. Commenting on one of the survey’s goals, Sager said, "If I were going to put a multimillion-dollar platform out there in deep water, I would sure want to have some information about sediment flows and mud volcanoes and things like that."

Another goal of the study was to discover the extent of these critters, since MMS has an obligation to protect these slow-growing, delicate gas-eaters. Sager has good news for the industry in that regard. He believes such life forms are neither rare nor ubiquitous. They seem to be plentiful enough not to require severe restrictions on exploration activity, but sufficiently dispersed to allow plenty of room for drilling.

One thing is obvious: These organisms are much better than humans are at finding hydrocarbon seepage.

That’s a big footprint. Schlumberger Geco-Prakla announced what it believes is the largest, unassisted seismic-vessel ‘footprint’. The footprint refers to the total area, in terms of streamer coverage, deployed behind a seismic vessel.

The Geco Orion towed six, 8,000-m streamers, each 200 m apart, which resulted in an 8-km² footprint. Larger footprints have previously been achieved, but only with the help of a second vessel used to maintain the spread (width) between streamers. For this unassisted record, the company used its newest Monowing technology (similar to an airplane wing positioned vertically in the water) to accomplish the 1,000-m streamer spread.

Ergodic what? Professionals in our industry frequently hear of spectacular new technologies. Most of these are "black boxes," operating on unknown or undisclosed laws of physics.

"Ergodic side-looking radar: the most powerful exploration tool in the world," claims Relucent Exploration Technologies Inc. It’s a method to detect hydrocarbon microseepage in the air above reservoirs. According to the company’s website (www.relucent.com), "This system identifies oil or gas accumulations by mapping the chemical reaction which occurs in the air when hydrocarbon microseepage enters a line of electromagnetic energy."

"The solar-lunar tides have a specific cycle during each month of the year, allowing us 5–7 days each month of optimum conditions for measuring the relucent effect of hydrocarbon molecules." The company claims that drilling on its recommendations "...results in production 75% of the time." Limitations to the technology are wet weather/soil, trees taller than 37 ft, rapid changes in barometric pressure and cultivated fields.

This writer does not endorse, nor has a clue as to the validity of, this technology, but nevertheless found it interesting. If you know of any emerging technology — whether good, bad or ugly — send us a line at: fischerp@gulfpub.com.

Copyright © 1999 World Oil
Copyright © 1999 Gulf Publishing Company