Full-azimuth, high-density, 3D single-point seismic survey for shale gas exploration in a loess plateau area, Southeast of Ordos Basin, China

摘要

Southern Ordos Basin contains plentiful oil and gas shale resources in the Mesozoic and Upper Paleozoic. It is known that the surface in this region is covered by thick loess layers with severe variations in tomography, thickness and velocity. The adverse surface conditions result in complex statics problems and heavy scattering noise and also cause serious absorption of high-frequency energy. Conventional seismic surveys obtain poor quality seismic data, which could hardly be used to obtain information about gas shale reservoirs. In order to study strong heterogeneous gas shale reservoirs and improve the success rate of horizontal wells, a new 3D seismic survey was acquired in the typical loess plateau area by using the WesternGeco UniQ integrated point-receiver land seismic system. The new survey is designed as full-azimuth, high-density, point-source/point-receiver in order to fully sample the seismic wavefield and avoid the irreversible signal damage caused by conventional field array techniques. By taking advantage of the benefits of UniQ seismic data, targeted data processing sequence is given to resolve the specific complicated statics and noise attenuation problems. Compared with the previously acquired 2D crooked line high-resolution seismic data in the gullies, the result of UniQ seismic data exhibits significant improvement both in the single-to-noise ratio (SNR) and the image quality of target layers. This indicates that the UniQ seismic data will be more feasible to facilitate gas shale characterization.