Prestack sweet spotting based on OBC data azimuth optimization: A case study of Liu3 Member in Weixinan Sag

To address the challenges of limited drilling data, low seismic resolution, and low accuracy of sweet-spot prediction for interbedded shale oil reservoirs in the third member of the Liushagang Formation (Liu3 Member for short) in the Weixinan Sag, a prestack meme inversion technique is proposed based on azimuth optimization of ocean-bottom-cable (OBC) data. A sweet-spot sensitive indicator is established through coordinate rotation of PI-SI cross plot and iterative optimization of the rotation angle based on petrophysical analysis. Under regional geologic constraints, predominant OBC azimuths for sweet-spot prediction are optimized to be parallel to provenance direction and perpendicular to major fault strike. Using optimized azimuthal data, prestack meme inversion is performed to characterize interbedded shale oil sweet spots in the Liu3 Member. Drilling results show that the method enables high-precision prediction of sweet-spot reservoirs even with sparse well control, achieving a success rate of well drilling over 80%. This approach provides an effective technical solution for offshore shale oil exploration with limited wells.