Reliable, clean, prestack data
During the mid 1990s, it became apparent that the imaging resolution available from land seismic technology was reaching a limit. Acquiring seismic data with ever-higher fold and source effort was not delivering the step change in image quality that the industry demanded. Therefore, WesternGeco commenced a research and development program to fundamentally redesign the technology and methodology by which the land seismic signal and noise are acquired, recorded, and processed. The philosophy behind the program was to engineer a system that would optimally sample both the signal and the noise such that all elements could be geophysically understood. The result of the development program is Q-Technology. Q-Land is the first generation and UniQ is the latest system. The fundamental point-receiver geophysics of both systems is the same.
Digital group forming
Q-Land and UniQ are integrated land seismic acquisition and processing systems. They use high-channel-count point-receiver technology to correctly sample the signal and the noise in the seismic wavefield. By correctly measuring the noise in the seismic wavefield, it can be geophysically removed. Digital arrays are formed and perturbation corrections applied to ensure signal preservation. Output traces are produced at the spacing required to correctly image the target. This process of noise removal and signal preservation is called digital group forming (DGF).
Random noise is removed on a trace-by-trace basis by custom designed modules. Coherent noise such as ground roll is removed by forming near-perfect KK filters that are not possible to apply if the input traces, or filter points, are too widely spaced, as is the case with conventional acquisition using analog strings of geophones or 3C surveys where the multicomponent receivers are widely spaced. The perturbation corrections made to each trace include static time shifts to correct for elevation differences plus amplitude compensation to correct for coupling variability. Collectively, these are referred to as intra-array perturbation corrections.
The resulting prestack data from Q-Land and UniQ are exceptionally clean, with a high signal-to-noise ratio, reliable amplitudes, stable phase, and wide frequency bandwidth. These data deliver the required step change in land seismic imaging, breaking the cycle of needing to acquire ever-higher-fold surveys, often with costly source and receiver efforts, in an attempt to stack out noise and improve the image.