by Mark Andersen
Thu, Jun 15, 2006 12:12 GMT
VIENNA, Austria - Improved imaging in the subsalt can be obtained by acquiring better seismic data, using several new methods. Jerry Kapoor, advanced imaging and asset development manager for WesternGeco, described several techniques to delegates here at the 68th annual EAGE (European Association of Geoscientists & Engineers) conference.
Currently, the industry is limited in the amount of information that can be obtained subsalt. Most of the subsalt energy interpreted in seismic sections falls between 5 and 20 Hz. Many existing techniques for processing seismic data attempt to improve the low frequency information content, but at the cost of loss of high frequency information.
"Our motivation is to get acquisition schemes to preserve low frequencies, and keep the high frequencies, as well," Kapoor said. "If the data are not recorded, there is a limit to what can be done in data processing."
Kapoor discussed the advantage of deploying a new over/under technique that uses vertically paired streamers. A test in the Gulf of Mexico using Q Marine* technologies demonstrated that this method provides cleaner seismic data, preserving both the low-frequency and high-frequency information. "We have found that being able to interpret top salt accurately is very important for subsalt imaging," he said.
He is also encouraged by other new methods. "We can get a step-change improvement in imaging subsalt by acquiring data differently; using a wide azimuth technique." Wide azimuth uses several vessels to broaden the area covered by the acquisition streamers. Another method is to use a multi-azimuth plan. By acquiring data over the same area with vessels moving in different directions—or azimuths—geoscientists can look at a structure from several directions.
A new method, which Kapoor termed 'rich azimuth' and described for the first time at this meeting, combines both wide azimuth and multi-azimuth recording. This combination of techniques, using Q Marine technology, enhances the bandwidth and provides better illumination of features below the salt.
For further information, contact Jerry Kapoor at WesternGeco.
Kapoor SJ, Stork C and Egan MS: "Benefits of Low Frequencies for Subsalt Imaging," paper G023 presented at the combined 68th EAGE Conference & Exhibition and SPE 15th Europec Conference, Vienna, June 12-15, 2006.
The EAGE Web site: www.eage.org.
Mark Andersen is executive editor of Oilfield Review.
*Mark of WesternGeco
© 2006 Schlumberger Limited.