An acquisition square template of 12 km x 12 km was simulated using a configuration that resulted in maximum inline and crossline offsets of 6,000 m with 200 m source and receiver line intervals. The acquired data set allowed the evaluation, through decimation, of many different options in acquisition of 3D land seismic data for exploration and development.
The assumption that long offsets with wide-azimuth geometries enable better multiple attenuation than narrowazimuth geometries was one of the main reasons for acquiring this first world-class full-azimuth 3D land survey in Kuwait. Other reasons were to enable reservoir characterization, in stacked carbonate reservoirs environment, using prestack inversion and to detect fractures using anisotropic analysis. The data set also allowed the analysis of the effectiveness of the full-azimuth approach in terms of velocity determination and imaging quality.
Two potential causes for loss of vertical resolution: NMOstretch and anisotropy, were handled in processing. Extensive mute tests were carried out to arrive at the best compromise between multiple attenuation and vertical resolution. Comparison between narrow and wide geometry was evaluated in 200m and 400m receiver and source line intervals data sets.
The effectiveness of this full-azimuth approach in 3D land seismic surveys in terms of velocity determination, multiple attenuation, imaging quality and reservoir characterization is evaluated and the challenges encountered in acquisition and processing are discussed.
Recording large 3D land seismic data, efficiently and economically, with improved vertical and spatial resolution, wide frequency range including low frequencies, full-azimuth and long offsets, is still a challenge. Dense spatial sampling and high-fold coverage which require a challenging high active channel-count are some of the main requirements for achieving success in such data acquisition The processing of wide-azimuth data also still faces many challenges.
A full-azimuth 3D land seismic survey over an area of 115 square kilometers was acquired in Kuwait. The acquisition design simulated a square template of 12 km x 12 km, one line roll, 200m source and receiver line intervals, and bin size of 12.5 m x 12.5 m. Thus, the survey has achieved inline and crossline offsets of at least 6,000 m and dense pre-stack spatial sampling of 5.7 million traces per square kilometer. The acquired data set allowed the evaluation, through decimation, of many different options in acquisition parameters for future onshore exploration and development 3D seismic surveys.
To restore symmetry, redundant traces were discarded before stack. The rose diagram of the ray paths for the simulated square template is shown in figure 1.
The primary objective of the survey was to maximize the resolution of the seismic data to enable detailed structural and stratigraphic interpretation, including establishing fault correlation and inferring lateral changes in reservoir properties. Other aims of this 3D full-wide-azimuth seismic survey were to enable the estimation of porosity variations within the reservoirs in a stacked carbonate reservoirs environment using prestack inversion and the characterization of fractures using anisotropy.
The assumption of a better multiple attenuation capability with long offsets and wide-azimuth geometry than with narrow-azimuth geometry was also one of the main reasons for using this full-azimuth geometry.
