Shallow water-deep gas is an attractive exploration target in south Louisiana.
Just like the overall "Old Faithful" Gulf of Mexico, exploration activity in Louisiana's long-productive coastal transition zone and adjacent shallow waters is a gift that keeps on giving.
Today, however, it's not the usual historically prolific targets shallower than 15,000 feet that are luring the operators. Instead, they're licking their collective chops over a whole new region: the deeper horizons harboring sizeable unexplored structures thought to contain, for the most part, enormous deposits of natural gas.
According to the U.S. Minerals Management Service, various reports and publications have reported five deep gas discoveries so far this year in the shallow water (less than 1,000 feet) Gulf.
But these deep, pricey wells virtually shout RISK in capital letters, requiring exceptional drilling expertise and a heap of confidence in the geoscientists' efforts to accurately identify the drilling target -- and there are no guarantees.
Look, for instance, at the Shell Oil Joseph well, which reportedly hit total depth at 25,000+ feet at High Island Block 10 off the Texas-Louisiana coasts early in the summer. The well is awash in rumors -- none of them celebratory at this point, e.g., dry hole, possibly productive from a portion of a 300-foot sand section, etc.
Because those in the know aren't talking, everyone else is left to speculate.
Providing still more thrills for those onlookers who thrive on uncertainty is the ExxonMobil Blackbeard deep gas well, which is anticipated to bottom out possibly as deep as 38,000 feet after a year of drilling: Mum's the word on the progress of this deep effort, at least for now.
The complex deep structures being probed by the drill bit encompass an array of fault systems and a host of ethereal salt and shale deposits. Not surprisingly, the indigenous reservoir systems are complicated.
Until now, seismic data to image these structures have been lacking both in quantity and quality. Fortunately for the prospectors, that's changing rapidly with a rash of acquisition programs and new technology (see related story, page 12).
But it's going to take more than good data to make this play a success, and a number of experts are focusing considerable effort on making it happen.
In fact, new techniques to reveal exploration opportunities in Louisiana's coastal and shelf areas was the topic of a paper that was slated for the September GCAGS meeting in New Orleans that was canceled by Hurricane Katrina.
"The deep plays are analogous in many aspects to the stratigraphically younger deepwater plays in the present day Gulf of Mexico," said co-author Fangjian "Jack" Xue, at Schlumberger Data and Consulting Services in Houston. "To gain a better understanding of the deep prospectivity of the south Louisiana transition zone, regional studies of the Miocene production trends have been integrated with high quality, deep-targeted 3-D seismic data, relevant publications from the industry and academia, and proprietary analysis and interpretation techniques."
Xue noted the study indicated the structural and stratigraphic framework of the area is characterized by a regional detachment surface at approximately 5.2 seconds (about 22,000 feet) under sand-rich Tertiary sediments. Above this detachment surface, syndepositional salt movement and associated growth fault systems have created extensive structural deformation.
"The lowstand system tracts dominate the section below 12,000 feet," Xue said. "The complex evolution history of the interaction between salt tectonics and slope sedimentation resulted in stacked reservoirs, high density of traps, multiple play types and abundant migration pathways in the deep section.
"The excellent geological conditions, together with relatively high pressure, created numerous, highly productive deep targets through most of the study area."
Given the challenge of the high potential/high risk aspect of the deep opportunities, the paper's authors determined special tactics are needed to minimize risk and maximize potential.
These tactics include:
- Sand-rich sequence identification.
- Accurate fault mapping.
- Hydrocarbon-bearing prediction.
- Multi-target penetration.