Albuquerque, N.M. — A small probe that can be inserted into a wellbore to measure downhole temperatures could save the American oil industry millions of dollars by allowing more effective treatment for paraffin accumulations in oil wells.
The probe was developed at Sandia National Laboratories and is being manufactured by Flexbar Inc. Flexbar is an oil-field equipment manufacturer based in Odessa, Texas.
Development of the downhole temperature probe grew out of a Sandia study of an oil field practice known as “hot oiling.” This is the practice of pumping hot oil, or in some cases, hot water into a well to melt paraffins that solidify when oil cools as it is pumped up the wellbore. These paraffins are a problem because they can gradually choke off production. Hot oiling is the first treatment used to prevent paraffin buildup. Chemical treatments or tubing scrapers also may be used.
Although each method has merits, they also have drawbacks, especially if used inappropriately, explains A.J. “Chip” Mansure, an engineer in Sandia’s Geoscience and Geotechnology Center. Because of the difficulty of getting real-time data, well operators have often treated for paraffin either too soon or too late. Premature treatment wastes money and risks unnecessary damage to the formation while treatment too late risks loss of the well.Mansure developed a battery-operated microprocessor/sensor module with a nonvolatile memory that can be placed in the well to record downhole temperatures during pumping operations. The module is put into a slightly elongated coupler (about 5 inches) that connects the sucker rods that pump oil to the surface. It is sealed into the coupler by a standard pipe plug. A well operator can easily attach several of the sensors to different sections of rods to get temperature data at various depths.
Prior to running the rod string into the well, the program controlling the start time and sample rate of the module is launched by a personal computer software program using an RS-232 interface adapter. When the rods are extracted, the temperature data is downloaded, plotted, printed, and exported to a spreadsheet by the software provided.
Although he originally set out to design all aspects of the probe, Mansure says he learned of a commercial temperature sensor with data recording capability made by Onset Computer Corporation that he thought could be modified to work in the downhole tool. Onset officials say these miniature devices, known in the industry as temperature loggers, were the same instruments used by the National Aeronautics and Space Administration to measure fingertip temperatures in space suits.
“We designed a housing for the logger, field tested the system, and then redesigned the housing based on the field tests to make it convenient to use,” Mansure explains. “We then conducted battery and temperature tests that determined that the logger could operate at higher temperatures than it was designed for. The final step in the development process was to contract with Onset to increase the memory and add a delayed start.”
Mansure says the temperature data will help well operators determine when and at what depth paraffin deposits are likely to occur and what treatments would be most appropriate. Because of its cost-effectiveness, Mansure expects the probe to be particularly attractive to operators of stripper wells, which are wells that produce less than 10 barrels of oil per day. Each year about 20,000 stripper wells are plugged and abandoned when they are no longer economic to operate.
The temperature probe was developed under the Natural Gas and Oil Technology Partnership, a cooperative effort of the U.S. Department of Energy, its national laboratories and the American petroleum industry.