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Dual-Gradient Drilling Project resumes

Posted on 15 November 2010

The industry Dual-Gradient Drilling Project that was begun nine years ago is back on track with a second well being planned for 2012. The world’s first well to be drilled using this technology was drilled in 2001. “Dual-gradient is moving ahead again, and this time I think it’s for real,” said Ken Smith, Manager of Dual-Gradient Drilling Project Implementation for Chevron. He was speaking at the IADC Annual General Meeting on 11 November in San Antonio, Texas.

What is dual gradient drilling (DGD)? The technology removes the mud from the drilling riser and replaces it with a seawater density fluid. A denser mud is used below the mud line to achieve the same bottomhole pressure as is done in conventional drilling. The differential pressure across the entire riser column is zero, meaning that it doesn’t need to be there to control wellbore pressures.

Using dual-gradient drilling technology on a deepwater well, casing points are selected=

Using dual-gradient drilling technology on a deepwater well, casing points are selected as if the well was onshore.

The technology itself is completely different than how we drill wells today. “It changes everything and how the people component is dealt with is really, really critical,” Mr Smith said. “The equipment we use is tested now, and we are very comfortable now with its robustness.” The DGD approach, in which the well is designed like an onshore well, offers advantages over drilling in deepwater – it  is possible to reduce the number of casing strings, a riser margin is in place at all times so disconnect well control hazards are reduced, drilling efficiency and mechanical risks are improved, and it allows for very rapid MPD-type operations.

The industry recognized the need to decrease the number of casing strings needed to drill in deepwater back in 1996. One challenging deepwater well, the Baja, exemplified this need. In DGD, according to Smith, mud weight is started from the mud line down, more closely paralleling the densities that nature has in place. Essentially the consequence is fewer strings of pipe needed. “That was the motivation,” said Mr Smith. About 15 man years of effort went into the drilling procedures and equipment through a JIP that was formed in the late 1990s. “Now we’re dusting them off and taking another look at them,” he said. “The reason we’re doing this is because it forms the basis for everything as we go forward.”

While the project was moving along nicely back in the early 2000s, the timing was out of sync, according to Mr Smith, in that Chevron had just finished building a new class of rigs. The DGD system is not easy to put on and take off a rig. Also, such technology took a big investment to get started.

Now, not only is the project back on the drawing board, it has progressed to the point where a rig named the Pacific Santa Ana, the first DGD-ready rig, is being constructed and expected to be delivered in the fourth quarter of 2011. Equipment has been built and tested, HAZOPS have been completed, and training on these systems will be completed. “All of these things will come together next year in the Gulf of Mexico,” said Mr Smith.

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