Enhanced prestack depth imaging of wide-azimuth data from the Gulf of Mexico: A case history

Abstract

We present a case study of enhanced imaging of wideazimuth data from the Gulf of Mexico utilizing recent technologies; and we discuss the resulting improvements in image quality, especially in subsalt areas, relative to previous results. The input seismic data sets are taken from many large-scale wide-azimuth surveys and conventional narrowazimuth surveys located in the Mississippi Canyon and Atwater Valley areas. In the course of developing the enhanced wide azimuth processing flow, the following three key steps are found to have the most impact on improving subsalt imaging: (1) 3D true azimuth surface-related multiple elimination (SRME) to remove multiple energy, in particular, complex multiples beneath salt; (2) reverse-time migration (RTM) based delayed imaging time (DIT) scans to update the complex subsalt velocity model; and (3) tilted transverse isotropic (TTI) RTM to improve image quality. Our research focuses on the depth imaging aspects of the project, with particular emphasis on the application of the DIT scanning technique. The DIT-scan technique further improves the accuracy of the subsalt velocity model after conventional ray-based subsalt tomography has been performed. We also demonstrate the uplift obtained by acquiring a wide-azimuth data set relative to a standard narrow-azimuth data set, and how orthogonal wide-azimuth is able to enhance the subsalt illumination.

Combination of improved acquisition system, processing, velocity model and migration for seismic imaging in areas of intense salt tectonics

“…Высокая эффективность этого ме-тода послужила причиной его вклю-чения в стандартный набор операций, который в настоящее время широко и успешно используется при изучении подсолевых отложений в Мексикан-ском заливе [Ma et al, 2011]. Этот набор состоит из 3D варианта SRME, уточне-ния скоростной модели среды путем сканирования временных задержек RTM (см.…”

“…Результаты миграции без компенсации (а) и с компенсацией (б) сейсмического погло-щения . изображении подсолевой толщи, что в дальнейшем принципиально повлияло на результаты интерпретации [Ma et al, 2011].…”

“…13. Результаты миграции широкоазиму-тальных данных из Мексиканского залива без применения (а) и с применением (б) SRME [Ma et al, 2011].…”

A case study: Improved subsalt imaging through TTI model building and imaging of a WAZ survey in the Gulf of Mexico

“…The Mississippi Canyon/Atwater Valley area has been extensively imaged using NAZ datasets (Whiteside et al, 2008) and WAZ acquisition (Baldock et al, 2009;Ma et al, 2010). It has been demonstrated that the introduction of anisotropy in the velocity model assuming VTI media, results in more accurate placement of events and general improvement of the image quality.…”

Automatic Interpretative Image-Focusing Analysis

“…When the migration velocity is correct, events within angle/offset gathers will be flat; when it is incorrect, they will either curve upward or downward. The use of focusing information within the physical axes as well as the angle/offset axis for image-focusing analysis has shown to provide high resolution and robust estimation of migration velocities in scenarios with limited aperture-angle range such as sub-salt imaging as well as narrow/constant-offset acquisition geometries (Sava et al, 2005;Wang et al, 2006Wang et al, , 2008Ma et al, 2011). Notwithstanding the success obtained with using all axes of a seismic image, typically velocity errors are assessed within seismic images using only the residual moveout information along the angle/offset axis.…”