Joe Zhou

Surface multiple attenuation in seabeach-shallow water, case study on data from the Bohai Sea

Summary Surface related multiple elimination (SRME) method is known to have difficulties in attenuating shallow water multiples. Particularly, for water-layer related multiples in very shallow water environment such as seabeach-shallow water areas because the primary water-bottom reflection that is required by SRME for predicting the multiples is not recorded due to near offset gap. Thus, in these situations, predictive deconvolution in either x-t or tau-p domain is often used in processing workflow to suppress this kind of multiples. However, deconvolution also attenuates primary events that have a periodicity close to that of the waterlayer. In this case study, we present a two-step processing workflow for removing free-surface multiples. Firstly, we use a multi-channel prediction filter estimated from the multiples for attenuating water-layer related multiples. Secondly, we apply SRME for suppressing other surface multiples generated by sub-surfaces underneath the waterbottom. We demonstrate that this workflow provides an optimal suppression of free-surface multiples on marine data that have been recorded in the Bohai Sea offshore eastern China.

Compensating attenuation due to shallow gas through Q tomography and Q-PSDM, a case study in Brazil

Summary The presence of gas, both as shallow pockets and as commercial reservoirs, has long been recognized as a significant problem in imaging seismic data. In this paper we describe how we successfully applied Q tomography and Q-PSDM technology to compensate the phase, frequency and amplitude loss due to shallow absorption, thus improving structure imaging and potentially accurate AVO/DHI analysis underneath shallow gas.

Anisotropic depth imaging with High Fidelity Controlled Beam Migration: a case study in Bohai, offshore China

Summary In the oil rich Bohai area, the Tanlu Fault zone plays an important role in hydrocarbon exploration and production. The strong velocity contrast across the high dipping fault structures, serious shallow water multiple problem and low signal noise ratio in the target zone prevent clear and accurate fault imaging from the conventional pre-stack time migration, previous attempt using Kirchhoff PSDM also failed to improve the image quality without first solving the low signal noise issues and creating accurate velocity model. In 2010, a complete reprocessing of the LD blocks using the most recent developments of the Pre-stack Depth Migration technology including the TTI (tiled transverse isotropy) model building and High Fidelity Controlled Beam Migration (HFCBM). Combined with the Shallow Water De-multiple (SWD) technology, the reprocessing provided a step change in the imaging quality in these areas, great improvement has been observed both in the structure images and signal noise ratio. TTI HFCBM should be considered as a viable tool to image the complex structure and decrease the exploration risk in this area.

Interferometric OBC Surface Related Multiple Attenuation

Surface-related multiples in Ocean Bottom Cable (OBC) data cannot be removed by directly applying standard SRME, which requires sources and receivers that are surface consistent. The ray paths needed for a complete surface-multiple prediction can be achieved by combining streamer and OBC data. The combination allows fully data driven SRME to be extended to OBC data. However, streamer data is not always available. In this paper, we demonstrate that the required data to predict surface-related multiples in OBC data can be constructed using inter-source and inter-receiver interferometry, and the multiples can then be predicted similarly as in SRME. The work flow does not require knowing any subsurface information.