GeoSciences

Waning wiggles?

Have we reached the end of the reflection seismic method? This was the question posed to me at a recent industry meeting. It set me thinking about how the “soundings” of the deep are produced and used, the constraints imposed by our processing capability, and the economic envelope that bounds the available techniques.

The short answer is, “No”. The longer answer is that certain methods are near their limits, but other methods are not yet ready to fully replace them. To add to the complexity, our need for better remote sensing continues to grow, forcing the industry to seek and employ new tools along with our existing set of very able techniques.

New tools are entering the seismic picture. ROVs and AUVs are finding a place in deploying/retrieving bottom-deployed sensors. These devices can minimize the number of surface vessels and crew needed to gather a survey. Satellite location and navigation systems reduce the uncertainty envelope for bottom sensor and improve repeatability.

Remote sensing choices continue to expand. Controlled source electro-magnetics and marine magneto-tellurics are two new forms entering the market.

Our current sensing and recording tools limit the seismic data we can collect. Only part of the signal produced by airguns is actually sensed and recorded. This subset is then massaged. Signal-to-noise improvements now let us gather more and better data, allowing more discriminating analysis.

The acquisition technique employed sets limits on phase, frequency, and azimuth available to the data processor and interpreter. Thus, initial data quality is key to any image developed from processing manipulation. The richer the data set, the better the image produced.

Processing algorithms are also a limit. The move to 3D seismic volumes forced enhancements to 2D processes and opened the potential for the extraction of more detailed images and better migration results.

The next limit, just now being explored, is 4C data (multi-component). Bottom-deployed sensors allow for expanded seismic data collection by adding shear wave data to the standard pressure wave information. For complex areas, the wider azimuth allows the structure-caused data distortions to be more correctly rendered.

But unsolved problems exist in interpreting the different wave modes and in linking P- and S-wave data sets. Horizontal velocity anisotropy is a major difficulty and is forcing a denser examination of the velocity field. Standard 1 sq-km sampling of velocity is no longer adequate to correctly process the data.

This places additional pressure on computer hardware to help seismic processors handle more data cycles. The computer industry has responded, producing cluster computing and high-speed linkages to major processing centers for handling ever-larger datasets.

Different acquisition methods have different cost structures and return data sets with different limitations. It is the oil company’s challenge to choose the best combination of acquisition and processing to address the explored region.

There is no foreseeable limit to the reflection seismic method except the limits of the earth to respond to our probing. We may be reaching the economic limit of towed streamer seismic as other methods provide better value in special cases, but the envelope of capability continues to expand to meet market demand. As that capability evolves, the wider set of tools and techniques creates new ways to solve the industry’s imaging problems.

NAPE

Upbeat and active, the annual NAPE prospect expo brought thousands of explorers to hundreds of opportunities for hungry exploration companies to consider. The IHS Forum, which preceded the exhibition, showed the vast array of opportunities available to companies of all sizes.

One clear conclusion is that the world has opened wide to independent oil companies. Their expertise is actively sought by host governments and potential partners since the majors are busy with large development projects, stock buybacks, and only the largest of exploration targets. Exploration money is already flowing for 2005 and the show demonstrated that the market for prospects is active once again.

EXPLORATION - Norway survey