Fluxgate directional assembly is composed of accelerometer sensor and fluxgate sensor, which is mainly used in mwd (measurement while drilling) to provide convenient and accurate data support for oil exploitation. This can reduce the cost of drilling and help operators better monitor the performance of equipment. At the same time, it can accurately measure the well angle, azimuth angle and tool face angle. This paper will mainly introduce the calibration of the sensor in the fluxgate directional assembly, which is divided into two parts: installation calibration and temperature compensation. So that the device can be more accurate output data.



Sensor installation calibration


Accelerometer sensor and fluxgate sensor are both essential sensitive devices for providing engineering parameters of the probe. In practical applications, the installation error of the accelerometer is an important factor affecting the measurement accuracy of the system. Although the installation error can be corrected by compensation method, the compensation accuracy mainly depends on the installation accuracy itself, and most of the accelerometer sensors and fluxgate sensors are packaged, which cannot be matched by mechanical or optical methods.

The fluxgate directional assembly to achieve 3 accelerometers and 3 fluxgate triaxial orthogonal, generally divided into the following steps: First, adjust the calibration frame to the horizontal state with the level, fixed the calibration frame; Secondly, the directional probe is fixed on the calibration frame, the directional component is connected to the computer, the computer is turned on, and the program is executed. Finally, the accelerometer sensor and fluxgate sensor are installed and adjusted one by one at a fixed angle until the sensor is triaxial orthogonal. The accelerometer sensor and fluxgate sensor are fixed at the measurement point with steel bolts in method 1.

After the installation and correction of the directional probe, the maximum error between the standard value of borehole inclination and the output value of the probe is ensured to be ±0.1°.



Temperature compensation correction of sensor


The accelerometer sensor and fluxgate sensor are the sensitive measuring devices in fluxgate directional assembly, and the temperature and the output signal of the sensor show a good linear change.



The main reasons for the temperature error of the accelerometer sensor are:

1. As the temperature rises, the torquer coil will become larger and more magnetic flux will be surrounded, which will increase the nonlinear error of the accelerometer sensor;

2. The thermal unbalance of the quartz flexible accelerometer will cause the support arm to produce a small deformation, causing the signal zero drift, so that the zero deviation change;

3. The temperature gradient inside the accelerometer package housing will change the air viscosity, resulting in a slight change in the zero deviation value of the accelerometer.



The temperature error of fluxgate sensor is mainly caused by:

1. Due to the increase of temperature, the magnetic flux of the magnetic core material will change slightly, which will increase the nonlinear error of the fluxgate sensor;

2. The internal thermal balance of the fluxgate sensor may cause slight changes in the external magnetic and excitation saturation.



Temperature compensation is to place the directional probe under different temperature conditions, record the output signals of 3 accelerometer sensors and 3 fluxgate sensors, and use the data compensation and data storage capabilities of the single chip computer to compensate the output signal to the output signal at normal temperature. Then the measurement accuracy of fluxgate directional assembly can be improved.



Conclusion


The fluxgate directional assembly adopts high-precision accelerometer and fluxgate sensor, which can be well adapted to the harsh underground environment and transmit measurement data in real time after strict installation correction and temperature compensation correction. ER-DOS-03 is a dynamic measurement fluxgate sensor that can operate at 150 ° C.

Experimental data can also be used to illustrate the situation. Table 1 shows the thickness and radioactivity of uranium deposits in each borehole. By studying the thickness and radioactivity content of sandstone type uranium deposits determined by logging data of 6 boreholes in the exploration area, the uranium enrichment area is divided into D4, D2 and D3 boreholes in the central and eastern part of the exploration area. Therefore, we believe that the comprehensive analysis of sandstone-type uranium deposits in coal-bearing strata by using the existing logging data is not only faster, but also greatly reduces the exploration cost of uranium deposits, and can save a lot of manpower, material and financial resources. The application fields of logging data will be further broadened and the economic and social benefits of logging work will be improved. Figure 1 and 2 show the contour maps of uranium deposit thickness and radioactivity of each borehole respectively.

Abnormal thickness and amplitude D1 D2 D3 D4 D5 D6
thickness（m） 1.20 2.80 2.25 2.30 1.80 1.10
amplitude（pA/kg） 1.35 7.40 7.23 7.70 2.10 1.80
Table 1 The thickness and radioactivity of uranium deposit in each borehole





Figure 1 Contour map of uranium deposit thickness of each borehole



Figure 2 Radioactive contour maps of uranium deposits in each borehole



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