SEMINOLE, Texas

The life of Seminole Field, which has been producing oil since 1937, has been extended and enhanced. The most recent regeneration of this prolific field is a three-part project led by Hess, operator of the asset with 34 percent ownership.
 
Hess engineers have been looking for a way to get more oil out of this stubborn formation for many years. The upper portion of this formation, known as the Main Pay Zone, has produced more than 660 million barrels of oil since 1937. However, there is still an estimated one billion barrels in the ground, so the potential here remains huge. The problem has been finding a way to move it out of what’s known as the Residual Oil Zone, commonly known by the acronym: ROZ.
 
The Hess Permian Subsurface team of engineers and geologists built a computer model of this 215-foot zone located just below the Main Pay Zone. The model was used to simulate conditions underground and to guide the design of the field implementation.
 
From that initial step, the project progressed in three stages:

• New and existing wells were drilled or deepened to reach the ROZ. There are 29 cells – a pattern of five well clusters, with one CO2 and water injection well in the center of four corner production wells per cell. These wells were connected to the existing field facilities with new pipelines and related infrastructure.
• The project also required the development of a grass roots project for producing and delivering pure carbon dioxide from the West Bravo Dome field in New Mexico. This work included drilling or redeveloping 47 wells, installing 60 miles of gathering lines and building a new electrical sub-station to provide power to drive the two huge 6,000-horsepower compressors installed on site
• The Seminole gas processing plant was expanded, adding 70 million cubic feet of gas processing capacity to the 210 mmscfd existing capacity, and improving the performance of the 25-year-old plant.

"Like most North American onshore assets, all of the easy oil in the Seminole has been produced," said Chuck VanAllen, vice president of Production for The Americas. "This is a challenging stuff. Getting it out requires capital, technical expertise and patience."
 
A Long History
 
The Hess connection to the Seminole goes back to 1969, the year Hess Oil and Chemical Corporation merged with Amerada Petroleum Corp. Amerada was an early player in what was called the Seminole Pool.
 
This partnership that owns what is officially known as the Seminole San Andres Unit was born in the 1960s when the companies with production in the large area got together to revive production by injecting water into the reservoir. The added pressure from the water flood helped push oil production to a peak of 70,000 barrels a day. During the 1980s carbon dioxide injection was added to sustain the output from the main production zone.
 
The CO2 causes a chemical change that is somewhat akin to the effect detergent has on a really greasy pan. Just running water does little to remove the grease. But adding detergent causes a change in the chemistry, allowing the water to wash off the grease.
 
In more technical terms, oil and water don’t mix due to interfacial tension. By injecting a miscible fluid instead of water, the injected CO2 is able to mix with the immobile oil and the mixed fluid moves from the injection well to producing wells
 
Other partners in this West Texas operation – still listed among the 50 biggest in the country – include Occidental with 28 percent; Exxon Mobil, 20 percent; Marathon Oil, 14 percent; Chevron, 2.5 percent and others with 1.5 percent.