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Hot, Harsh, and Hostile

Fri, 01/28/2011 - 10:13am
Pamela Aparo, Analog Devices, Inc.

 On an oil rig, problems can boil over quickly; a new class of electronics goes to extremes

Pam AparoOut on the wind-swept North Sea, an oil drill is attempting to penetrate hard rock. The ocean is frigid but a few miles under the seabed, the thermometer hits a hellish 200°C. Volatile weather conditions and temperature ranges make drilling hazardous and complex. As the drill bit pounds away at the earth’s rocky skull, the extreme vibration adds to an already harsh environment. And with much of the world’s easily accessible oil already extracted or unavailable, contractors must drill ever deeper – placing even more stress on system components and materials.

The high-temperature challenges of designing for the oil and gas industry are legendary. But now the high-temperature electronics market is heating up with products designed from the ground up for down-hole drilling. For the first time, instrumentation amplifiers are available that are guaranteed to work at temps as high as 210°C, thus setting a new industry standard. More robust inertial sensors are emerging to address the drilling operator’s myriad data acquisition needs. And advances have been made to decrease power consumption in extreme environments.

Oil Rig

Drilling platforms such as the one pictured are demanding drill heads with more rugged, sophisticated electronics capable of exploring oil and gas reserves in increasingly extreme environments.

Oil and gas exploration presents a superset of everything that can go wrong in an industrial environment. It’s probably no exaggeration to say that the only thing tougher is space exploration. Just as the lack of suitably rugged electronics has hampered such high-temperature applications in the past, now their availability can help to advance the field. Case in point: a prime patch of oil off the Continental Shelf in the Atlantic Ocean off Brazil was considered unfeasible from a technology standpoint. Investors in the recent Petrobras public offering, however, took the plunge, apparently deciding the rewards far outweighed the risks.

There are difficult trade-offs, and designers in this space must face the challenges “head on” since the electronics are strategically located just behind the drill head. To meet the challenges, designers must keep in mind these crucial issues:

Packaging must stand up to the more punishing conditions. As the instruments travel miles into the earth they are exposed to extreme temperature, vibration, and shock on the way down. This drives designers to use larger, through-hole packages in their systems, and, in higher temperature applications, ceramic packages. While many systems are rated at 150°C to 170°C in order to service lower temperature wells, new designs are targeting 210°C and hotter. By comparison, most commercial electronics have a maximum operating temperature of only 85°C to 125°C. Extremely hot temperatures amplify differences in how different metals and other compounds behave under stress, so materials analysis is all the more important.

Oil drilling scenarios include monitoring conditions in a well that has been drilled (wire-line well logging) and measuring conditions as the well is being dug, known as measurement-while-drilling (MWD) or logging-while-drilling (LWD). In the latter case, the system provides some measurements as the drill bit moves, such as rotation and vibration, and other measurements – such as soil conditions, pressure, and radioactivity – at periodic intervals.

Parts must be proven. Electronic parts should be characterized, and ideally production tested, at high temperatures. In some applications designers can take advantage of products developed specifically for this market. For example, the AD8229 low noise high temperature instrumentation amplifier was designed to meet the demands of extremely hot and noisy environments and successfully tested at 210°C. Parts are expected to perform at least 1,000 hours at that elevated temperature. Each ceramic-packaged AD8229 is tested by Analog Devices before shipping to the customer.

It’s hard to overestimate the pressure of locating a pocket of oil when the operator is several miles removed from the sensor head. When you’re that far removed from a potential problem, what do you do? Process technology must be advanced enough to handle the higher performance demands of extreme operating conditions and faint signals. Advancements in the area of Silicon-on-Insulator (SOI) components allow electronics to withstand the rigors of deeper and hotter exploration, making them more likely to survive the mission. If a part fails the cost is sky high: the drill-string or wire-line tool is extracted and replaced at an expense ranging from about $40,000/hour to upwards of $1 million a day, depending on location.

Space is at a premium -- and so is power. Inside the narrow drill pipe there’s not an inch to waste. This is at odds with the need to use leaded, through-hole packages for stress relief from vibration and thermal expansion of the board. To overcome this challenge, designers often must build their own multi-channel modules (MCMs) because otherwise the large, ceramic packages that survive temperatures over 200°C would limit the amount of electronics that can be placed on the narrow boards.

There is also a huge premium on power to the electronic devices. A new class of MEMS sensors, rated for operation over 175°C, has lowered power consumption by an order of magnitude, from over 10 mA to under 0.5 mA per axis.

As designers put together smart systems aimed to go miles and miles under the earth’s surface, they are challenged to balance power, size, and space requirements against the need for more information. Conditions on oil rigs of the future will only get harsher as oil deposits become harder to find. Electronic components will have to function in even more rugged and noisier environments then they do today, placing a real premium on developing high-temperature systems. As a leader in high-performance data-conversion and signal-conditioning technologies, Analog Devices is ready to help designers face these extremes.

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