Emerson Exchange 365

by Jim Montague

When you take oil from the ground, it’s often important to know where the hydrocarbons end and water begins. For example, crude oil from the Eagle Ford Shale formation in south Texas is particularly light and sweet for North America. It's gathered in 25-30-ft. tanks that are subject to paraffin build-up, and emulsions of water and dirt come along for the ride.

“Tank management means knowing how much oil, how much water and how long before the tank fills,” said Jared Edwards, field sales representative and pressure level and temperature specialist for Emerson Process Management. He reported that guided wave radar (GWR) is the technology of choice for pinpointing both top level and interface measurements because it:

• Performs a top-down measurement with no extra penetrations below the liquids;
• Is not density dependent like floats or pressure measurements; 
• Has no moving parts; and 
• Generates wave plots that can greatly aid troubleshooting.

Edwards and Brendan Shackedford, technician in Emerson’s Instruments & Valve Services, described the challenges faced by several oil producers in the Eagle Ford region, and showed some of their best practices for overcoming them. Their presentation, “The Upstream Oil and Gas Interface Challenge” was delivered this week at the Emerson Global Users Exchange.

Emerson’s entry-level GWR solution is its Rosemount 3302. A more sophisticated option is the Rosemount 5302, which is more robust, generates more powerful signals and performs better in particularly difficult applications. Notably, the 5302 has advanced, direct-switch technology, and so its signals aren’t split as they travel out and back along transmitter’s cable, which preserves and returns 100% of its signal. Traditional, two-wire GWR transmitters use transformer or bridge solutions for transmitting and receiving, and so only 25% of the signal makes it back to the receiver.

Besides the usual challenges of delivering power to remote sites via solar panels, batteries or generators, Shackelford reported that many tanks and GWR components have to deal with grounding issues, too. “Our customers found that grounding rods didn’t provide the best solution, and that their communications also suffered,” said Shackelford. “As a result, burying grounding mesh with multiple points is the best solution for remote tank batteries.”

Meanwhile, water intrusion sometimes hampers GWR transmitters and components, so it’s important to use Teflon tape between connections and plug any extra conduit entries.

In addition, dielectric values can also change because paraffin builds ups in tanks over time. It floats on the produced water and below the crude, and further reduces the interfaces dielectric value. This makes it important to flush out these build-ups when possible.

Also, it might seem obvious to cut GWR transmitter cables to the right length, so they can measure all the oil in a tank, but not hit the bottom and bend. However, many users apparently overlook a few important details that can make a significant difference, according to Edwards. “Users are typically very concerned about the last 12 inches of their tanks in order to keep any emulsion out, which could ruin a load, and cause them to lose a day,” he said. “So, to get true tank height, it’s important to remember to measure from the top of the flange. Likewise, it’s also important to measure probe length from the bottom of the GWR transmitter to the top of the weight. This is the custom length that is entered into each GWR transmitter.”