Chevron ultradeep well shows high production

Chevron said Thursday that a test well it drilled through a thick layer of salt more than 5 miles below sea level had a high rate of oil production, an indicator of the promise of an emerging field in the Gulf of Mexico.

The test well at the St. Malo field, located about 280 miles south of New Orleans, had a production rate of more than 13,000 barrels of oil per day, the company said.

The well was drilled in waters 7,000 feet deep and reached 20,000 feet below the seafloor. At a total depth of more than 5 miles, the well is part of a growing effort by energy companies to reach for more challenging reserves in layers of rock that are difficult to read and massively expensive to target.

Seismic readings of deep geologic formations located under thick layers of salt are especially challenging to produce and analyze. And drilling at extreme depths involves the high expenses of ultradeep-water drillships and the challenges of high pressure and heat in underground rock formations. Setting up those fields for production requires companies to remotely install networks of undersea machines more than a mile underwater that manage the flow of oil to multibillion-dollar production platforms.

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The daily cost of simply operating an ultradeep-water drillship regularly exceeds $500,000, and can climb higher than $650,000.

Chevron’s test well was drilled into the Gulf’s “Lower Tertiary Trend,” in a rock formation known as the Wilcox Sands.

The Wilcox Sands are a thick layer of sand that was formed by a type of underwater “avalanche” to spread vast amounts of sediment across the area tens of millions of years ago, according to Chevron.

The well’s flow rate is the highest of any well drilled into the formation so far, according to Chevron.

Chevron has a 51 percent stake in the St. Malo field. Petrobras has a 25 percent share, Statoil owns 21.5 percent and ExxonMobil and ENI each have 1.25 percent stakes in the field.

Wells drilled in the St. Malo field and the nearby Jack field will feed into a production platform that is expected to take in an estimated 94,000 barrels of oil equivalent per day from the fields, Chevron said in a news release.