Metrological laboratory for the calibration of downhole survey instruments

On the basis of the Novosibirsk Scientific and Technical Center, there is a metrological laboratory for the calibration of borehole directional survey instruments. It is located in a freestanding wooden building that houses only non-magnetic equipment. During the construction of the laboratory, copper fasteners were used to exclude their influence on the magnetic background, with which the downhole directional instruments work. A laboratory of this level is the only one beyond the Urals.
The non-magnetic calibration device allows you to rotate the borehole inclinometer weighing up to 100 kg in any direction in three axes. In the laboratory, they work only with high-precision reference instruments, which allow achieving errors of up to 30 arc seconds. The laboratory can simulate the actual operating conditions of downhole tools (for example, heat, vibration and shock).
“For calibration it is necessary to create such conditions that there is no influence of electromagnetic devices and external factors. In addition, it is also necessary to measure the Earth's magnetic field very accurately. Therefore, non-magnetic objects are needed - so that there are no reinforced concrete grids or iron structures. Accordingly, the best option is a wooden structure. Staples and nails were used to a minimum, ”explained Dmitry Taylakov, technical director of the NSTC, Ph.D.
The following directions of the device act as three axes: in the direction of the magnetic azimuth (conditional north), in the direction of the zenith (vertical, direction of gravity) and the direction of rotation along its own axis.
“By placing the device inside the installation, we can simulate the rotation of the tool in the borehole at any given angle in the azimuthal, zenith and apsidal (direction of proper rotation) directions. The rig measures the actual angles, allowing you to compare them with the readings of the borehole inclinometer, thereby controlling its accuracy. Thus, the inclinometer in the borehole regulates the direction of drilling with a known accuracy, which is one of the important factors in the correct performance of the work. If this is not done, the drilling result may be completely unsatisfactory. For example, an underground part of a well may extend beyond the cadastral territory, which will lead to huge problems with the legality of production from the owner. Among other things, we have developed a special self-learning neural network calibration algorithm in order to further increase the reliability of the readings of the instruments supplied to our laboratory, ”says Konstantin Tukmachev, NSTC lead engineer.
A specially developed digital algorithm takes into account all data and errors. Other companies use installations that work only at 3-8 points of spatial coordinates. The installation of the NSTC allows measurements in three axes at various temperature conditions, thereby reaching the number of points over 50 thousand, increasing the accuracy and usefulness of the data obtained.
“This is the only laboratory of this level beyond the Urals. There are English attitudes in Tomsk that are as close as possible to what we are doing. But the cost of their installations is about 30 million rubles. We have managed to achieve significantly lower costs with the highest accuracy. The installation, together with all the additional devices, costs about 8-9 million, which is three times cheaper than foreign analogues, "added Konstantin Tukmachev.
Another advantage of the NSTC non-magnetic calibration facility is that foreign counterparts do not have metrological traceability. British engineers solved this problem, but in an expensive way, by installing three multifaceted sitall prisms and a reading device - an autocollimator. Today such prisms are not produced in Russia. And the closest analogs - steel prisms cost 1.5-2 million. In addition, such installations have a significant drawback - the physical number of angles is limited by the number of prism faces. The NSTC installation uses a theodolite with a resolution of 20 arc seconds, which allows obtaining accurate data with a resolution that is 1.5 thousand times greater than for the largest prism.
“In addition, we have worked out a calibration option in temperature ranges. This is not the case in any domestic installation. There are thoughts on further modernization, but so far this is just a concept, it is still far from their implementation, ”says Konstantin Tukmachev, leading engineer of the National Science and Technology Center.
Today the main customer of measurements in the metrological laboratory is NNPGA "Luch" - a permanent partner of the NSTC, with which the center has been working for a long time. But work is underway with other manufacturers of inclinometric equipment. So, within the framework of the study of the laboratory's capabilities, work was carried out with the instruments of the American company "Tolteq". On the basis of these obtained measurements, our employees, together with the State Center for Testing Measuring Instruments SNIIM, entered inclinometers into the Russian state register.