"Straight Down," Feature Article, March 2003

straight down

Working steel in the ground makes a wider well.

This article was prepared by staff writers in collaboration with outside contributors.

A Houston company is selling a different kind of well. Deep ones for oil and gas usually telescope, or get narrower as they go down, because each new section of casing has to fit through the ones above. Enventure Global Technology LLC, though, says it has gotten around the restriction, with a well that has no taper at all. Located in Starr County, Texas, the well represents a development of the company's SET process, which cold works steel pipe to expand its diameter. The trademark letters stand for "solid expandable tubular."

In the SET process, the first length of pipe in each section has a conical tool mounted in a small vessel at the lower end.

When the section is in place, the crew injects fluids into the well to drive the cone back up. As it works its way through the pipe, the tool stretches the steel.

A tool forced through the pipe expands a SET well casing.

According to Kevin Waddell, vice president of engineering at EnventureGT, the original SET process reduced, but didn't eliminate, telescoping of the well casing. It has been used in more than 100 wells in about six countries since 1999.

The company, a joint venture of Halliburton Energy Services and Shell Technology Ventures, has lately improved the method to give a well the same inner diameter from top to bottom. According to Waddell, the tool itself has been modified, and the new method adds a second working of the steel, from the top down.

The well in Starr County was completed for Shell last September. EnventureGT calls the new system Mono- Diameter.

Most SET installations have used low-carbon steel from Lone Star Steel Co. of Lone Star, Texas. The pipe, made to EnventureGT's specifications, is heat-treated to increase ductility, so the steel can be expanded into the plastic region without rupturing. Some wells have required the corrosion resistance of stainless pipe, which came from other suppliers.

SET technology requires a connection that will remain sealed before and after expansion. EnventureGT worked with Grant Prideco, a Houston supplier of drilling and marine products and services, to develop a threaded connection that doesn't increase the tubular's wall thickness. Grant Prideco performs the precision threading, which is held to an even tighter tolerance than the pipe itself.

EnventureGT used finite element analysis software from Ansys of Canonsburg, Pa., to work out design requirements. The software calculated the deformation and sealing capacity of the threaded connections, and determined the properties of the pipe after expansion.

Depending on the application, the pipe wall can start anywhere from a quarter to four-tenths of an inch thick. Expansion will usually reduce the wall thickness by 4 to 10 percent.

According to EnventureGT, the cold-working requires a pipe wall thickness that varies by no more than 8 percent. It's a tighter tolerance than permitted by the standard of the American Petroleum Institute, which allows 12.5 percent.
The assembly of pipe into sections requires special tools, designed to spread friction over a wide area of surface. That's because dents or other irregularities created by conventional tools will interfere with the pipe expansion.

The company also uses Ansys software to analyze downhole fluid conditions in the field.

EnventureGT has suggested that the value of Mono-
Diameter technology is that drillers can reach greater depths if a well doesn't have to grow tighter as it sinks into the Earth.
SET may also save money because the hole can start with a smaller diameter than conventional methods would need for reaching a given depth.

Meanwhile, David Miller, director of standardization at the American Petroleum Institute in Washington, said that API members seem to be interested because of another advantage. Miller said they've talked about it as a means of putting a larger pipe into the strata to get a greater volume of fluid flow.
According to an EnventureGT executive, the innovation of the product lies in the application, not in the basic principle.

"Cold working of steel isn't new," he said. "No one has done it downhole before."