FOG Inclinometer Measure Theory And Components

Fiber optic gyroscope inclinometer is inertial measurement system which based on inertial navigation technology. It is a kind of device which doesn't depend on any external devices, completely independent of real-time and rapid measuring instrument. Its basic principle is based on Newton's laws of puts forward the relative inertia space mechanics. Using of fiber optic gyro, accelerometer sensitive instruments the angular velocity and acceleration in the process of moving along the well hole, then get parameters at well hole location, such as Inclination, Azimuth, depth etc., this is the description of well bore trajectory.

Introduction

Gyro drilling inclinometer is a kind of drilling trajectory measuring instrument which is not affected by geomagnetic interference and surrounding magnetism. It is mainly used for drilling trajectory measurement in magnetic mining area, casing, drill pipe, etc. Of course, it can also be measured in other drilling holes which are not affected by magnetic interference.

Compared with the gyroscope used in aviation, the gyroscope used in logging has the following characteristics due to the influence of its operating environment. First of all, the volume requirements are strict, especially the diameter is small, and the instrument is required to adapt to the diameter requirements of the casing well after formation, and even can be invested from the drill pipe when opening the skylight; Second, it has strong vibration resistance, which will not damage the gyro body when the test drilling is opened or put into the bottom hole. There are also wide temperature requirements, that is, the instrument can work normally in the 125° environment for at least 2 hours and the overall accuracy of the instrument meets the design requirements in the ambient temperature range of -10-125°.

In terms of structure and manufacturing process, gyroscopes can be divided into mechanical gyroscopes, optical gyroscopes and semiconductor gyroscopes. The mechanical gyroscope includes frame gyroscope, dynamic tuning gyroscope, liquid floating rate integral gyroscope and electrostatic gyroscope. Optical gyroscopes are mainly laser and fiber optic gyroscopes. The most common semiconductor gyro is silicon micro gyro.

Among these gyroscopes, the manufacture of electrostatic gyroscopes is extremely difficult and expensive, only the most sophisticated weapon systems are used, and the technology is only mastered in a few countries in the world, so it will not be applied to other fields in the short term. Silicon micro gyro has low precision and large temperature drift, although it has good vibration resistance and ideal volume, some people are doing the discussion of forming instruments, but due to its own technical development level, it is now mostly used in dynamic camera feedback loop detection, and there will be no ideal logging products for a considerable period of time.

At present, the gyro used for logging covers almost all kinds of mechanical gyroscopes, including frame gyro, dynamic tunable diaptometry gyro and fluid floating rate integral gyro.

Fiber optic gyroscope inclinometer is a inclinometer that uses fiber optic gyroscope element to determine the inclination Angle of borehole. Application of fiber optic gyroscope in gyro inclinometer: It is usually necessary to use gyro inclinometer to measure the inclinometer azimuth value in cased-well skylight and old well retest. In abnormal magnetic field areas and well sections, due to the large error of the fluxgate measurement value, gyro inclinometer is also needed to measure the azimuth value. In addition, in some specific circumstances, such as the high frequency of solar magnetic storms, or the need for a third instrument to verify the occasion, gyro inclinometer also has its unique role.

Working principle

Fiber optic gyroscope is actually a kind of angular velocity sensitive element based on Sagnac effect. The Sagnac effect is that when a light beam travels in a circular channel, if the circular channel itself has a rotational velocity (angular velocity), it takes more time for the light to travel in the direction the channel is rotating than it does to travel against the direction the channel is rotating. In other words, in both forward directions, the optical path of the two beams changes relative to the optical path of the channel at rest. If two beams of light advancing in different directions interfere to measure the rotation speed of the loop, an interferometric fiber optic gyroscope can be created. If this change in the optical path of the loop is used to realize the interference between the light constantly circulating in the loop, that is, by adjusting the resonance frequency of the optical fiber loop and then measuring the rotation speed of the loop, a resonant fiber gyroscope can be manufactured. Fiber optic gyroscope has high precision and sensitivity.

The basic optical devices of fiber optic gyroscope include light source, coupler, polarizer, fiber coil, detector and so on. The components of the fiber optic gyroscope are mostly semiconductor devices, which are connected to each other by plugs and are directly welded to the printed circuit board. The use of fiber optic gyroscope in petroleum instruments overcomes almost all the shortcomings of mechanical gyroscope, such as poor vibration resistance, magnetic field changes, drift torque factors, work is greatly affected by ambient temperature and so on. Fiber optic gyroscope (FOG) is a kind of azimuth sensor suitable for gyroscope inclinometer. The main defects of fiber optic gyroscope are the high cost of the component and the poor resistance to high temperature. In order to ensure accuracy, more and more fiber turns are used, resulting in a relatively large volume. The solution is to install a high-efficiency thermos bottle to ensure that the maximum operating ambient temperature of the fiber optic gyroscope is below 80°, which can basically meet the measurement needs of the well depth within 4000 meters. Corresponding to the diameter limit of the well, the diameter of the optical fiber can be reduced effectively by changing the winding way of the optical fiber, which can meet the requirements placed in the drill pipe.

Peculiarity

More advanced fiber optic gyroscopes have reached a sensitivity of 0.01 degrees/hour. Compared with silicon micromachined gyroscopes, the angular velocity sensitivity is several orders of magnitude higher. Using its high sensitivity of diagonal velocity, we can use it to measure the angular velocity vector of the earth's rotation, and then calculate and process to determine the tilt orientation of the drill hole. This azimuth is the direction relative to the Earth's North Pole, known as the true North azimuth. This kind of gyroscope inclinometer is called self-seeking north gyroscope inclinometer, which is the most widely used horizontal inclinometer (geoscience instrument).

Conclusion

The gyro inclinometer uses inertial navigation technology to carry out drilling measurement. It makes use of the characteristics of inertial navigation device with strong autonomy, high navigation accuracy and good reliability. It adopts a strapdown north finding system composed of fiber optic gyro and accelerometer sensors to measure the rotation rate of the earth through the gyro and the gravity acceleration of the earth through the accelerometer. Then the top Angle, azimuth Angle and tool face Angle of drilling hole are calculated by relevant formulas.