It is widely held that the Gulf of Mexico (GoM) ultra-deep sediments hold the promise of potentially significant new oil and gas discoveries. But revealing these hidden treasures will require a holistic understanding of the petroleum system at the basin level. This means imaging deeper (to 60,000 ft – 18,300 m – or more) to see major structural elements and better understand salt evolution with higher resolution at all depths to identify more subtle isopach variations and stratigraphic features.

GulfSPAN, developed by ION’s GX Technology group and led by Adrian McGrail, is the basin-level tool that offers an ultra-deep 17,000-mile (27,200-km) 2-D seismic dataset spanning the entire western and central portions of the GoM. It is the first and only basin-scale multiclient seismic program available in the GoM. It was conceived in response to an industry need for new regional datasets that overcome limitations of legacy seismic so as to provide a basis for future exploration.

ION has teamed up with INEXS, a geological and geophysical interpretation consulting company, to reinterpret the GulfSPAN dataset using the latest imaging technology, reverse time migration (RTM). The objectives are to offer a product that will lead to better understanding of the regional geology and, more specifically, the deeper, less explored areas of the basin. The seismic and structural interpretation aspect of the project encompasses newly reprocessed legacy land data and new ocean-bottom cable (OBC) acquisition integrated into the long-offset streamer data that is the heart of the GulfSPAN dataset. Ultimately, the interpretation process of the GulfSPAN data will provide geologic guidance for velocity model-building; thus providing a more comprehensive dataset that companies can integrate with other 2-D and 3-D datasets for a more comprehensive view of the entire area. This will enhance the current understanding of the interaction between stratigraphy, extensional zones, faulting, and folded features along with detachment surfaces and salt bodies.

The GoM’s subsalt is challenging to interpreters, going way beyond Salt Interpretation 101. However, these salt structures are associated with many of the GoM’s largest recent discoveries, including Thunder Horse, Mad Dog, St. Malo, and Jack. GulfSPAN, which uses advanced seismic processing technologies and highly skilled geoscientists, overcomes the problems inherent with typical salt interpretation by enabling top-to-bottom imaging of the salt structures. Kirchhoff, BEAMS, and RTM are the migration algorithms for the velocity model-building process. RTM works by running the wave equation forward in time for the source and backward in time for the receiver. RTM properly propagates the wavefields through the most complex velocity regimes, including salt. Transforming seismic wave travel times into depth is considered the most difficult aspect of imaging. When building velocity models that include high-velocity salt structures, the iterative process is an essential step. However, GXT’s implementation of RTM greatly enhances the speed and accuracy of the velocity model-building process.

The GulfSPAN project has already provided insights including identifying the systems that were responsible for the generation of the Perdido and the Port Isabel fold belts, which were formed at the same time but in two different positions, as well as a more complete understanding of the Wilcox deposition from shelf edges to deepwater fans. These and other insights into the GoM come from the application of these technologies since 2001, when GulfSPAN was conceived. The first geological velocity models, 2-D data, and interpretation were delivered to licensees in 2004. In the initial GulfSPAN, 3,800 line-miles (6,080 line-km) were acquired with an additional 8,500 line-miles (13,600 line-km) added shortly thereafter. The next iteration of GulfSPAN happened within a couple of years, when 1,081 miles (1,730 km) of OBC and 3,500 miles (5,600 km) of land data were incorporated for a program total of 17,091 miles (27,345 km). During this project phase, called GulfSPAN Merge, more than 150 segments of various vintage land data were merged with the OBC and streamer data. The GulfSPAN Merge endeavor adds 2-D lines that go from Dallas to the deep waters of the GoM, yielding an unprecedented look at the evolution of the GoM

ION has also delivered ultra-deep seismic SPANs and advanced depth imaging in basins near Africa, the Arctic, Brazil, Colombia, Caribbean, India, Nova Scotia, and the Northeast Atlantic. The repeated worldwide application of long-offset 2-D seismic SPANs and evolving RTM methods is peeling back the veil concealing ultradeep reserves within regional petroleum systems and their subsalt structures.

The broad scale view offered by GulfSPAN provides knowledge into what hydrocarbon treasures the GoM still hides.

The GulfSPAN program layout was planned with the specific goal of better understanding the regional geology and the deeper, less explored areas of the basin. (Image courtesy of INEXS and ION)