BP Aims for a Bull’s

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By Henry Fountain

HOUSTON — To hear the people at Baker Hughes tell it, a drill string — length after length of narrow pipe that can extend for miles into the earth — is far from a rigid assembly of high-strength steel. It is more like a wet noodle.

"The challenge is not to get it to bend," said Aravindh Kaniappan, a product manager for Baker Hughes, a drilling equipment and services company. "It's to get it to not bend."

Because a string of drill pipe, along with the rotating bit at its cutting end, tends to go this way and that, drillers need critical information about the location of a well as it is being drilled.

"First you need to know where you are," Mr. Kaniappan said. "Then you need to know from where you are, where you need to go."

The need for accurate location information — in a subterranean environment that Global Positioning System satellite signals cannot reach — is true now more than ever, as oil and gas wells go deeper and become more complex, veering off horizontally through narrow hydrocarbon reservoirs or parallel existing wells.

But it is especially true right now in the Gulf of Mexico, where BP is drilling a relief well to intersect the runaway well that has been spewing oil since April.

The relief well will be used to pump heavy drilling mud, followed by cement, into the damaged well to stop the gusher permanently. But first it, or a second relief well being drilled nearby as a backup, must hit the target — the existing well's steel casing pipe, only seven inches in diameter, more than 3 miles below the surface of the gulf.

The first relief well is currently about 20 feet horizontally and less than 1,000 feet vertically from the interception point. "We feel very good about the progress we’ve made," Kent Wells, a BP vice president overseeing the relief well effort, said at a recent news conference, but did not revise an estimated completion date of early August.

Baker Hughes and other companies are helping BP reach the target, providing specialized techniques and tools for measuring and surveying the relief wells as they are drilled, and steering them in the right direction.

Many of these services — variously described as "measuring while drilling," "logging while drilling" and "directional drilling" — are used in almost all wells, and have been for decades. But the techniques have been improved and expanded over the years, aided by advances in sensors and processing.

Baker Hughes and companies like Halliburton, Schlumberger and Vector Magnetics use sophisticated accelerometers and magnetometers to determine the inclination, or angle, and azimuth, or compass direction, of the hole, sending the data back to the drill rig as binary pulses in the drilling mud that circulates through the drill pipe. If the drill bit has strayed, it can be steered back on course by several means, one of which uses pressure pads against the well bore to change the bit's direction.

With the relief wells, magnetometers are also being used to locate the target, by detecting the electromagnetic field created by an electric current induced in the runaway well's casing pipe. The relief wells are then being steered closer and closer to the intercept point, nearly 18,000 feet down.

More than direction and location, though, sensing tools — hollow pipes that resemble thin, shiny torpedoes, up to 30 feet long, with sensors and processors installed in precisely machined cavities — can help oil companies better understand rock and hydrocarbon reservoirs, often in real time as they are drilling through them.

"During the last five to 10 years there has been a step change in the technology," said Mattiass Schlecht, Baker Hughes's vice president for drilling systems. Tools measure the natural gamma radiation emitted by rock, the electrical resistance of any fluids within, and even, through a kind of inverse M.R.I. device, the magnetic resonance of the nuclei of hydrocarbon atoms.

Gamma measurements can determine whether the bit is drilling through sand (which is more likely to contain hydrocarbons) or shale. Resistance information shows whether the formation contains oil, gas or water. And nuclear resonance data indicates how easily the oil will flow out of the porous rock. "How much of that fluid you can really move out of the pores and into the well bore," Dr. Schlecht said.

Stephen Prensky, a consultant in Silver Spring, Md., who follows trends in drilling technology, said that many of the changes have been evolutionary, improvements to existing measurements using newer electronics. But the move toward more real-time data collection is crucial, he said, with deepwater and other complex wells costing upward of $100 million.

"You want to have as much information as possible to make sure you drill the best well possible," Mr. Prensky said. "Real-time information is essential in those circumstances."

But even in relatively simple vertical wells, measurement and other data is crucial. Geologists may have mapped the various rock formations in advance based on seismic surveys, but formations are far from homogeneous, so it can be important to know precisely what kind of rock the well has traveled through. And a well cannot be allowed to veer across a lease line, for example.

Drill bits stray all the time, as the bit encounters pockets of softer or harder rock. "Drilling straight down doesn't necessarily mean you go straight down," said Scott Schmidt, Baker Hughes's president of drilling and evaluation services. "The bit wants to follow the path of least resistance."

In any well, one goal is to keep the well bore smooth and any turns gradual, avoiding what drilling engineers call "high dogleg severity."

"Once you have a kink in there it will hurt you for the rest of the well," Dr. Schlecht said. It will create higher friction for the drill string, he said, and make it more difficult to send casing pipe down the well.

Decades ago, well surveys were done only after pulling the drill pipe out of the hole, a process that, depending on depth, could take a day or more. Instruments were lowered on a wire, readings were taken, and the instruments were brought back up. (Some of the earliest equipment, called single-shot tools, actually took a photograph of a compass rose lowered deep in the hole; drillers would have to wait for the film to be developed to determine azimuth.)

Now the high-tech tools usually form a permanent part of the drill string, assembled at the very end. Together with the drill bit, perhaps a mud-driven motor to rotate it and steering equipment, the tools form a "bottom hole assembly" that can be well over 100 feet long — and easily worth several million dollars, particularly since the bit is usually encrusted with synthetic diamonds.

Because the tools form part of the drill string, they must be hollow to allow the drilling mud to pass through to the bit, where it provides lubrication and cooling and carries the rock cuttings back to the rig. That makes the job of the tool designer more difficult, as all the sensors, silicon chips and power supplies have to sit in the walls of the pipe. At a long and low building near Houston's international airport where Baker Hughes makes its tools, workers regularly perform extreme feats of machining, like drilling a small hole for wires down through 30 feet of pipe wall.

Not all the tools can provide data while the well is being drilled, however. Accelerometers, tiny silicon devices that measure gravitational pull along three axes, work best when there is not much external vibration, so drilling is usually stopped to take measurements, although the drill pipe remains in place.

Magnetometers work best when there is no magnetic interference from other steel, so in the early stages of drilling BP's relief wells, "ranging" runs to determine how close the relief wells were to the runaway well were performed with the drill pipe pulled out of the hole and a separate magnetometer lowered on a wire. A device sent a current into the formation, inducing a current in the metal casing pipe of the runaway well. The magnetometer detected the field created by the induced current, and software sorted out the signal to determine the distance to the pipe.

In later ranging runs, however, the drillers have been using a faster system that does not require the drill string to be pulled completely out of the well. The system also has a sensor directly behind the bit, which gives drillers a more accurate reading of the most important piece of information: where the actual bit is in relation to the runaway well.

Those magnetometers are connected to the surface by a wire that can handle a lot of data. For other tools that form part of the drill string, however, data is usually sent to the rig through mud pulse. A simple valve raises and lowers the pressure in the mud inside the drill string, and a sensor on the rig measures the small pressure changes.

With the data being transmitted at about 10 bits per second, it takes about 30 seconds to transmit basic measurement data, and that is with much of the data being crunched in processors on the tool.

That is glacially slow by modern standards, but as Mr. Kaniappan describes it, still a remarkable feat to distinguish the small pressure changes that make up the signal from all the background noise. "It's amazing the technology we have," he said.

An article on Tuesday about the digging of relief wells to intercept and plug the oil leak in the Gulf of Mexico referred incorrectly to the nature of rock formations. They are "far from homogeneous," not far from "heterogeneous."

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