A high resolution 3D case study from offshore Thailand demonstrates that a pursuit of 2D symmetric sampling principles, complemented by high density 3D streamer acquisition, a compact source array, and shallow source and streamer towing, can yield comparable temporal resolution to a 2D site survey. The high spatial continuity of the new 3D data provided the optimal platform for a tailored highresolution processing sequence, yielding an outstanding tie between well data and seismic, and delineating individual stacked sand bodies and complex en echelon fault structures.
Pearl Oil (Thailand) Ltd acquired a high-density, highresolution 3D seismic survey in 2004 to establish an accurate geological framework for development drilling of the Jasmine Oil Field in Block B5/27, offshore Thailand. The main zone of interest is in the range of 0.3 – 1.3 s TWT, with hydrocarbons being trapped within a stacked sequence of Miocene fluvial sandstones and shales. The fault pattern in the survey area is typical of a right-lateral strike-slip system, represented by hundreds of closely spaced en echelon normal faults along the trace of the underlying master fault. Small anticlines form the basic hydrocarbon-trapping mechanism within closures on both sides of the normal faults. The new 3D seismic program was acquired in 2004 to image the faults clearly, as well as to map the top, base, and lateral extent of each sand body. Most notably, a key survey objective was to yield useful frequencies as high as 150 Hz at the target depth, as had been achieved with a high-resolution 2D site survey in 2000. All new 3D survey objectives were achieved as a result of careful survey planning and execution.
Survey planning was designed to give particular attention to the following principles of high-resolution seismic imaging: ? The frequency bandwidth of primary reflections recorded on to tape must be as large as possible. Recorded frequency bandwidth is a function of source array design and, most notably, the source and streamer towing depths. Decreasing source and/or streamer depth corresponds to increasing frequency bandwidth, increasing operational noise, and decreasing signal-to-noise ratio. ? The recorded frequency bandwidth will ideally be preserved throughout the entire processing flow. In practice, multi-channel filtering operations and prestack migration are all explicitly dependent upon tight spatial sampling to avoid aliasing effects of dipping events, and the associated loss of higher frequency content. Therefore, both inline and cross-line bin size must be as physically small as possible. Cross-line bin size typically places the strongest constraint upon highest recoverable frequency in processing. ? Tight 3D spatial sampling (small, square bins) and high 3D trace density will optimize pre-stack migration coherency and frequency bandwidth. ? Every subsurface point at the target should be properly illuminated during acquisition, and should have reflected seismic energy with a uniform distribution of source-receiver offsets and azimuths. If such an illumination criteria is satisfied for all target points, then a very high quality, high resolution seismic image of the target should result from processing, free of processing-induced noise (artifacts) and degraded resolution (Long et al., 2003).
