Originally an exploration tool, reflection seismic has evolved into a valuable reservoir imaging technique.

The introduction of 3D, and now 4D, has opened new, important applications involving more accurate reservoir delineation for reduction of drilling risk, better reserves calculation and production optimization. The latter derives from more precise location of drainholes and a clearer understanding of reservoir drainage over time.
Just as a surgeon runs a battery of exhaustive tests before operating on his patient, drillers need an accurate picture of the reservoir before they drill. The penalty for putting a well in the wrong place is paid over the life of the reservoir and can be economically disastrous. Today's medical teams possess a variety of modern imaging tools - ultrasound, magnetic resonance imaging and cat scans - to complement the ubiquitous X-ray. But what tools are available to the drillers?
Since its early days, seismic technology has evolved on two parallel paths, acquisition and processing. With a few exceptions, acquisition - the way a wavefield is sampled - has remained the same for the past two decades. For onshore surveys, crews deploy large analog arrays of geophones, and the recorded signals are summed electrically, then digitized. At the same time, advances in computer technology have allowed great strides in the ability to process seismic data.
At the 1988 European Association of Geoscientists and Engineers conference in The Hague, Netherlands, Shell's Leo Ongkiehong surmised the perennial problems of acquisition - noise and distortion - that dramatically limit bandwidth, could be alleviated by discretely recording each geophone channel. Ongkiehong identified more than a dozen separate errors that perturb the measurements. Most of these are compounded when the data are electrically summed, making deconvolution virtually impossible (Figure 1). By single-sensor recording, spatial samples could be handled the same way as temporal samples, he said. This would simplify the data acquisition to a general measuring system and subsequently provide endless processing possibilities. Twelve years passed before a practical solution was developed.
In 1994 a consortium of companies working under the Thermie project published a comparison of array and single-sensor data that validated Ongkiehong's premise. Resolution of the processed data showed marked improvement even with an eightfold reduction in the number of sensors (Figure 2). However, at the time there was limited ability to simultaneously record large numbers of discrete samples. Even today, the most sophisticated recording devices can barely handle 3,000 channels, which translates to only 1,000 three-component geophones. Acquiring definitive data in complex geology with such a small sampling capability is not cost-effective, even if it were possible.
A new technique, called simply Q, promises a solution. The system, introduced by Schlumberger at Geo2000 in Bahrain, offers 30,000 channels recordable in real time at a 2-msec sampling rate. With this many discrete channels, geophysical solutions are effectively decoupled from the hardware, providing clean, distortion-free signals to the processors. A software technique - digital group forming - allows data to be shot once and processed multiple times to achieve optimum results for each particular target. By moving the group forming from the geophone array to the processing unit, a more flexible solution is available. Some of the advantages of Q are said to include:
enhanced image quality for better location of wells;
full compatibility with multicomponent techniques;
improved 4D due to highly repeatable data;
imaging of multiple levels from a single shoot;
simultaneous downhole and surface acquisition;
better vertical resolution because of higher bandwidth; and
lighter arrays to achieve the same results.
What is the potential impact of this new technology? Hart's E&P put the question to Ongkiehong. He grinned. "Impact is the product of quality and acceptance," he said. With single-channel recording, the quality is possible.