Seismic Imaging: Today and Tomorrow

Thursday, Dec 18, 2008

According to WesternGeco's Houston-based research director, recent advances in processing capabilities are allowing sophisticated seismic data migration methods to become standard practice.

Dave Nichols, speaking before a recent gathering of geophysicists and engineers, said improvements in imaging are taking advantage of the increases in computer capacity that enable imaging techniques that are closer to the ideal wave equation. They are also benefitting from new acquisition geometries that extend the frequency bandwidth and offset and azimuth range of recorded data.

New acquisition geometries such as wide-azimuth, multiazimuth, rich-azimuth, and Coil Shooting single-vessel full azimuth acquisition deliver increased illumination of the subsurface from a wider range of angles and azimuths. These new techniques enhance the accuracy of the inversion of seismic data for Earth properties. In addition, increasing the frequency bandwidth by lowering the minimum frequency of seismic sources has improved steep-dip imaging and overall resolution.

Migration techniques that honor the actual physics of wave propagation are an important factor in improving image quality. There are two main trends active here: reverse-time migration and anisotropy. Both have been studied for many years, but only now are adequate computer resources available to make use of these tools in an integrated approach of imaging and Earth property determination.

In the future, the industry will have to go beyond correctly positioned images and deliver estimates of absolute Earth properties. In a traditional compressional-wave, or P-wave, workflow, this process has been split into two parts: acoustic-imaging algorithms that yield accurate Earth reflectivity and elastic reflectivity inversion that provides a model of the Earth properties.

Today, tools like full-wave inversion are available to combine these steps into a single estimation of absolute properties directly from the wavefield. While current computer power makes this process feasible only for acoustic models, in the future that capability will extend to elastic full-wave inversions and incorporate other measurements, such as electromagnetic and gravity data.

"We will continue to ride the wave of computer power," Nichols said. "When I joined the company almost 15 years ago, we were at tens of megaflops. We've seen a million-fold increase in computer power. I expect to see another thousand times increase before I retire."

Source: Schlumberger