Texas A&M University

Petroleum Under Pressure By Susan E. Cotton

Growing worldwide demand for oil is pushing gas prices at the pump higher and higher. Technology developed by Texas A&M petroleum engineers may help us reach new reservoirs.

Hans Juvkam-Wold
Hans Juvkam-Wold, holder of the John Edgar Holt Endowed Chair in Petroleum Engineering, has been developing dual-gradient drilling technology for more than two decades. Jerome Schubert
Assistant professor Jerome Schubert began studying dual-gradient drilling as a graduate student under Juvkam-Wold. Now the two are collaborating to advance the technology.

When you pull up to the pump at a gas station, it’s easy to forget how that gas got there.

Drilling for the oil that ends up as gasoline in your fuel tank is complicated, expensive and sometimes dangerous. We’ve used up most of the easy-to-get-to oil. The oil that’s left — and the experts agree, there’s still a lot there — is hard to get to, a lot of it under thousands of feet of water in the Gulf of Mexico and the North Atlantic and North Pacific oceans.

Dual-gradient drilling may help. Petroleum engineering researchers say dual-gradient technology should enable drillers to get to reservoirs unreachable with current technology and make the process safer at the same time.

This is where petroleum engineers Hans Juvkam-Wold and Jerome Schubert come in. Their work on dual-gradient drilling is moving the technology from laboratory simulations closer to the deep blue waters of the Gulf of Mexico or the North Atlantic and the oil beneath.

Juvkam-Wold, professor and Holt Chair in the Harold Vance Department of Petroleum Engineering, has been working on dual-gradient drilling technology since the mid-1990s. Assistant professor Jerome Schubert began working on the technology as one of Juvkam-Wold’s graduate students.

Back to (deepwater) basics

To understand dual-gradient drilling, you need to start with conventional (single-gradient) drilling.

Drilling for oil underwater has been going on a long time and it’s pretty routine. When you drill an oil well underwater, the hole in the seafloor is connected to the platform or drill ship on the surface by lengths of drill pipe. The drill pipe carries the bit that actually drills the hole. Drillers pump thick goo called drilling mud down the pipe to cool the bit and carry away debris the bit chews out of the rock.

With dual-gradient drilling, the drilling mud is pumped back to the surface through a separate line. This pumping lets drillers control “kicks” before they become blowouts. With dual-gradient drilling, the drilling mud is pumped back to the surface through a separate line. This pumping lets drillers control “kicks” before they become blowouts.

In the shallow part of the well (the first 3,000 to 4,000 feet below the seafloor), the mud simply flows back up the space between the pipe and the walls of the hole and out onto the seafloor, where it stays. (This is known in industry jargon as “pump and dump drilling,” Juvkam-Wold says.)

This region can be the trickiest part of drilling the well. It’s where so-called shallow hazards — rock formations that often contain water, natural gas or pockets of frozen methane gas — may occur. When this water  — usually under abnormally high pressure — and the methane get into the bore hole as the bit drills through, they can burp back up toward the surface (a kick), with potentially disastrous consequences. Uncontrolled kicks can turn into blowouts that can damage the well, drilling equipment, and the people operating the well.

Blocking the kick

After this shallow section is drilled, drillers place segments of larger-diameter pipe, called surface casing, around the drill pipe and cement it into place. Once this foundation-like assembly is in place, a large valve known as a blowout preventer is installed, followed by another pipe called the marine riser that encloses the drill pipe all the way to the surface.

The blowout preventer allows drillers to control pressure in the drill hole, important if the bit grinds into that natural gas or fresh water. The riser allows drilling mud to be pumped all the way to the surface for recycling instead of dumping it on the seafloor.

This is the conventional approach, known as single-gradient drilling, and it works fine in relatively shallow water. The problem is that most of the oil beneath shallow water is gone. The oil that remains is in deep water: Much of the remaining reserves lie beneath water at least 10,000 or 12,000 feet deep.

Drilling deep

Drilling in deep waters

Drilling in water deeper than 5,000 feet seems costly and risky — why spend the money and take the chance?

“There’s oil there,” says Hans Juvkam-Wold, professor in the Harold Vance Department of Petroleum Engineering and holder of the John Edgar Holt Endowed Chair in Petroleum Engineering. “And gas. You have to go where the hydrocarbons are. The main disadvantage is cost.”

A floater, an offshore platform or ship that supports the drilling, is the better part of about $500,000 a day; a whole well, about $50 million. (So the price of gasoline shouldn’t take you by surprise, he says.)

“The United States has produced maybe 80 percent of the easy oil already — that’s just my number,” Juvkam-Wold says. “To keep producing, we have to go into the deep water.”

It’s true, the Arctic has oil pools, too. But drilling in ultradeep water pays off more than drilling in the North Pole, he says.

“I’ve been in the oil business all my life — since I got out of high school and went to South America,” Juvkam-Wold says. “You go to where the drilling is.”

The usual approach to drilling in deep water begins much like what happens in shallow water, except that the drill pipe is enclosed in a larger pipe, the riser. Instead of pumping and dumping, the mud is pumped down the drill pipe to the bit and then recycled back up through the riser to the surface, where it is recycled.

If the drillers can “close in” the well at the seafloor they have more ability to control these burps, or kicks, with the blowout protector. The whole assembly is similar to the foundation of a building in reverse, Schubert says. The cement and surface casing anchor and stabilize the well below them. But the mud still poses a problem. If the mud is flowing uncontrolled back to the seafloor with no means of shutting in the well, it’s very hard to control the kick and regain control of the well.

Enter the dual gradient

Dual-gradient technology offers a way to deal with this puzzle. With dual-gradient drilling, the mud doesn’t flow back up through the riser to the surface. Instead of the riser, a separate seafloor pump and line carry the mud to the surface for cleaning and reuse. Valves in this pump system allow drillers to circulate out a kick before it escalates into a blowout, which could damage drilling equipment and platform, as well as endanger the crew.

Using dual-gradient technology requires drilling companies to look at drilling technology that’s different from what they’re used to using, Schubert says.

“In their minds, this is untried, expensive technology and nobody wants to be first,” he says.

This mindset may be changing. A test well using dual-gradient technology has been drilled in the Gulf of Mexico in 1,000 feet of water, and the technology worked as Juvkam-Wold and Schubert’s simulations had predicted. And two major energy companies are considering using dual-gradient technology to drill new wells soon.

“We know it works,” Schubert says. “We just have to convince the industry that it’s a worthwhile investment.” end of story