Those darned deepwater explorers are at it again. They just can’t be happy unless they’re pushing technology to the limit. Their most recent target is the Lower Tertiary trend in the Gulf of Mexico, characterized by deep water, deep targets, and deep salt, all of which add up to deep, well, you get the gist.

But the hardy few who have taken on the challenge are starting to see some pretty serious rewards. James Cearley, general manager of Gulf of Mexico Deepwater Expllration for Chevron North American Exploration and Production Co., recently addressed the Houston Geological Society to discuss the challenges and potential rewards of this huge play.

In charting the industry’s march into deeper water over the past 60 years, Cearley said “Every 10 years we did the equivalent of a moon shot.” It started with the Lower Miocene in 1947 and was followed eventually by a move to the shelf, deepwater mini-basins, the flex trend, the fold belts, and finally the deepwater subsalt efforts taking place today.

The resource isn’t as large as the Miocene – 3.4 Bboe of total discovered resource compared to 9 Bboe for the Miocene – but the success rate in the Lower Tertiary Wilcox as a whole is better, at 44% compared to 40% in the Miocene, and even the subsalt Wilcox, a challenging play with 2.7 Bboe in total discovered resource, brags a 40% success rate. These deeper plays are also very underexplored compared to the Miocene.

The Lower Tertiary Wilcox is a 300-mile-long, primarily subsalt trend in ultra-deep water that targets some of the oldest and deepest clastic reservoirs ever developed in the Gulf. Oil fields discovered to date have been very large with significant thicknesses, but flow rate challenges due to low-permeability rocks and low-mobility hydrocarbons provide significant completions and production hurdles. Cearley said the Jack well test was an important milestone in confirming the producibility and commerciality of the pay in these deep fields.

He outlined challenges all along the value chain, from imaging to production. Imaging challenges have been greatly enhanced by the move to wide-azimuth seismic acquisition, which he said was a “game-changer for the deep water. Comparing narrow-azimuth to wide-azimuth on Jack, we’re seeing fine details not discernible on the narrow-azimuth. And that’s not all of the story. On Tahiti, on the original velocity model, we couldn’t see against the salt. But with our new velocity model, we can see events going right up to the salt.”

Drilling challenges are numerous and include storms and hurricanes, vortex-induced vibration, loop currents, high-pressure gas stringers, pressure regions and thief zones, high-pressure/high-temperature issues, and challenges to casing design. “In a simple salt canopy, you might have five or six casing strings,” he said. “In more complex canopies, you need more strings, and it requires an intricate casing design.”

Choosing the right production system is also a challenge, and several are being considered, including spars, semisubmersibles, tension-leg platforms, etc. Petrobras will be bringing the Gulf’s first FPSO to produce its Cascade and Chinook fields, which are also in this trend.

Ultimately, Cearley said, the key to unlocking the value of the Lower Tertiary Wilcox trend will be the practical application of existing technologies, the rapid maturation of new technologies, and the efficient sharing of infrastructure development. “These fields have world-class potential, and there are lots of opportunities in the subsalt reservoirs,” he said. “But they’re at significant water depths, and we’re fighting temperature and pressure.”