Low frequency passive seismic technology studies in oil and gas fields worldwide have successfully identified characteristic spectral anomalies that correlate to the location and geometry of hydrocarbon reservoirs.
Action in the North Sea. Photos courtesy of Spectraseis.
For the first time, however, an offshore trial is under way to determine the applicability of this direct hydrocarbon indicator (DHI) technology as a means to directly confirm prospects -- prior to drilling -- in the marine environment.
The program is a collaborative effort between Norsk Hydro, Scripps Oceanography and Spectraseis, which developed the low frequency spectral analysis DHI technique being implemented.
The locale is the non-producing Astero field in 350 meters water depth on the Norwegian shelf sector of the North Sea. Hydro drilled both a discovery and an appraisal well at Astero, which is north of the giant Troll oil field.
“We’re transforming the technology from onshore to offshore the first time,” said Peter Hanssen, principle geophysicist at Norsk Hydro oil and energy research centre in Bergen. “It’s the first worldwide test offshore.”
A recoverable OBS node being deployed during a survey of a proven non-producing oil field in the North Sea using high-sensitivity ocean bottom seismometers. The green pressure sphere contains the receiver. Photos courtesy of Spectraseis.
The environment precludes placing sensors by hand, which is the MO for this technology onshore. Instead, Scripps is supplying ocean bottom sensors (OBS), which will drop to the seabed to record the low frequency data -- the natural noise of the earth induces the signal that the OBS will pick up from the reservoir.
“For the future, if the test is positive, it will change how we look for oil worldwide in any area,” Hanssen said. “It will have immense implications.
“It’s a dedicated exploration tool,” Hanssen added. “Once we’ve established it works, we’ll want to go where we haven’t drilled before and have prospects we want to analyze. You can check your prospect and focus your expensive 3-D active seismic survey on a specific promising area instead of doing the whole block.”
The two-week-long data acquisition phase of the North Sea program was scheduled to wrap at press time, with processing of the data to follow.
Final results are expected by September, according to Spectraseis CEO Ross Newman.