With the increasing difficulty of oil exploitation, directional well has become an essential drilling method for oil exploitation. In order to ensure that the drilling tool can be constructed in the downhole according to the designed oil layer, the importance of measuring instruments while drilling has become increasingly prominent, and the fluxgate directional assembly is an important part of it.

The directional probe based on fluxgate directional assembly can further improve the measurement accuracy and application range of the directional probe by taking advantage of the data compensation ability and data storage ability of the single chip microcomputer. It can not only carry out single point measurement and multi-point measurement, but also carry out wireless measurement after adding different data transmission modules to provide the data about the direction of the drill bit. The data collected by the directional probe can be used to ensure high quality completion of the designed well trajectory of the directional well and horizontal well.

In this paper, the basic structure of directional probe, the basic structure of fluxgate and its working principle are discussed.

Basic structure of fluxgate directional assembly

The directional probe uses the gravity accelerometer sensor and the fluxgate sensor to continuously measure the gravity field and magnetic field parameters under the condition of the downhole instrument, so as to calculate the inclination angle and azimuth angle of the borehole and transmit them to the surface instrument through the mud pulser. The surface instrument continuously records the borehole inclination, orientation, well temperature and other engineering parameters corresponding to the borehole depth in real time.

The directional probe mainly consists of two parts: electronic circuit module and sensor module.

The electronic circuit module is mainly divided into four parts: power electronic circuit module, main control electronic circuit module, signal electronic circuit module, vibration electronic circuit module.

The sensor module is mainly divided into accelerometer sensor and fluxgate sensor. See Figure 1.

As a measuring nipple that provides directional well engineering parameters, the directional probe mainly provides engineering parameters such as inclination angle, azimuth angle, high edge tool face, magnetic tool face and temperature. These parameters can ensure that the unique state of downhole instruments in space can be determined by accelerometer sensors and fluxgate sensors no matter what state the directional probe is in.

Figure 1 A component of a directional probe

The basic structure and working principle of fluxgate

Fluxgate is a sensor used to measure weak magnetic fields, such as the earth’s magnetic field. There are many varieties of fluxgate sensors, but the working principle is basically the same. The magnetic core materials of fluxgate sensors are mostly soft magnetic materials, which generally have high magnetic permeability and low coercivity. A drive coil and an induction coil are wound on the magnetic core. The alternating current is loaded onto the driving coil, and the driving magnetic field consistent with the driving coil can be generated according to the principle of electromagnetic induction. When the external magnetic field pair is perpendicular to the direction of the input axis, the fluxgate output is 0; When the direction of the external magnetic field and the input axis of the fluxgate is not vertical, the state of the magnetic core will change, and the external magnetic field on one side of the magnetic core will be superimposed with the excitation phase, making the electromagnetic saturation increase, and the external magnetic field and the excitation phase on the other side of the magnetic core will be reduced, and the electromagnetic saturation will be reduced. At the same time of alternating excitation magnetic field, the magnetic core changes linearly from the saturation region, and the pulse voltage of different sizes is induced on the two windings. The voltage amplitude is affected by the size of the external magnetic field and the frequency is 2 times of the excitation frequency. Figure 2 shows the working principle of fluxgate.

Figure 2 Fluxgate working principle diagram

Conclusion

With the increasing number of directional wells and horizontal wells and the improvement of required accuracy, the importance of directional probe is becoming more and more prominent. The ongoing need to reduce drilling costs has led to the creation of new technologies such as directional probing. The fluxgate directional assembly adopts high-precision quartz flexible accelerometer and fluxgate sensor. After strict installation correction and temperature compensation correction, it can adapt to the harsh downhole environment, transmit measurement data in real time, and guide drilling. Reduce drilling costs and improve drilling efficiency.

Ericco develops a wide range of fluxgate directional assembly, including dynamic and static measurements, for measuring well angle, azimuth angle and tool face angle. For example, ER-DOS-03 is a dynamically measured fluxgate directional assembly that is shock and vibration resistant and can operate in harsh, high-temperature environments. The ER-OS-07 is a static measurement fluxgate directional assembly that can operate at temperatures up to 150 ° C.

If you are interested in learning more about fluxgate directional assembly, please contact us.

Application of Fluxgate In Fluxgate Directional Assembly