ABSTRACT

As a type of carbonate reservoir and main oil-gas production formation in the Tarim Basin, China, fractures and paleokarst caves in Ordovician limestone are the targets of interest for seismic exploration in the S48 well area. Although conventional 3D, high-density, and wide-azimuth seismic acquisition has been widely applied in the Tarim Basin, we still need to determine what 3D 3C seismic data can further do for the characterization and fluid detection of the carbonate reservoir. In the S48 well area of the Tahe oilfield, we had acquired 3D 3C seismic data with single digital 3C sensors at the same grid, whereas the traditional 1C acquisition had arrayed geophones. Through comparison and analysis of two kinds of seismic data, including field records and migration profiles, some important characteristics can be found: (1) The z-component of the 3C seismic records has a higher dominant frequency and wider frequency band, but a worse signal-to-noise ratio, compared to the 1C receiver. (2) The P-wave migration profiles from the 1C and 3C seismic data have the same imaging quality for different subsurface structures. Further interpretation and seismic attributes analysis with these two kinds of seismic data reveal that (1) the amount of small-scale caves, recognized by the P-waves from the 3C seismic data, is relatively more than that recognized from the single component, (2) compared with the coherence and curvature analysis of the P-wave, the accuracy of fracture recognition is improved greatly with the PS-wave, based on S-wave splitting and verified by dipole S-wave logging, and (3) the seismic attributes related to multiwaves can detect the oil reservoir more accurately than when only P-waves are used.

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