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SUMMARY
The gyroscope drilling inclinometer is a drilling trajectory measurement instrument that is not affected by geomagnetic interference and surrounding magnetic fields. It is mainly used for drilling trajectory measurement in magnetic mining areas, casing, drill pipes, etc. Of course, it can also be used for trajectory measurement in other drilling holes that are not affected by magnetic interference. Compared to aircraft gyroscopes, logging gyroscopes have the following characteristics due to the influence of their usage environment. Firstly, there is a strict requirement for volume, especially for a small diameter. It is necessary to form an instrument that can adapt to the wellbore diameter requirements of the casing well, and even be able to be inserted from the drill pipe when opening the skylight; Secondly, it has strong anti vibration properties, which will not damage the gyroscope body when drilling the skylight or putting it into the bottom of the well; There is also a requirement for a wide temperature range, which means that the instrument can work normally in a 125 ° C environment for at least 2 hours and the overall accuracy of the instrument meets the design requirements within the ambient temperature range of -10-125 ° C. From the perspective of structure and manufacturing process, gyroscopes can be divided into mechanical gyroscopes, optical gyroscopes, and semiconductor gyroscopes. Among them, mechanical gyroscopes include frame gyroscopes, dynamically tuned gyroscopes, liquid floating rate integration gyroscopes, and electrostatic gyroscopes. There are mainly two types of optical gyroscopes: laser and fiber optic gyroscopes. The most common type of semiconductor gyroscope is the silicon micro gyroscope. Among these gyroscopes, the manufacturing of electrostatic gyroscopes is extremely difficult and expensive, and only the most advanced weapon systems are used. The technology is only mastered in one or two countries in the world, so it will not be applied to other fields in the short term. Silicon micro gyroscope has low accuracy and large temperature drift. Although it has good vibration resistance and ideal volume, some people are exploring the formation of instruments. However, due to the limitations of its own technological development level, it is now mostly used for feedback loop detection such as dynamic imaging. For a considerable period of time, there will not be ideal logging products. The logging gyroscopes currently available cover almost all types of mechanical gyroscopes, including frame gyroscopes, dynamically tuned gyroscopes, liquid floating rate integration gyroscopes, etc.
Frame gyroscope
Frame gyroscope is the earliest and most mature classic type of gyroscope, which is easy to manufacture, inexpensive, and has good anti vibration performance. The theory of frame gyroscope is very mature in countries such as the United States and Russia, and some foreign brands of gyroscope inclinometers such as "Harris" use frame gyroscope. Its structure is shown in Figure 1.
Figure 1 Frame gyroscope structure diagram
The rotor support element of the dynamic tuning gyroscope uses flexible support instead of ball support in the frame gyroscope. The gyroscope body consists of a rotor, flexible joint, sensor, torque converter, and drive circuit. The structure is shown in Figure 2. The flexible joint consists of three rings: upper, middle, and lower, which are the key components determining its working quality. Compared with the frame gyroscope, due to the improved structure of the rotor part and the use of rigid and sensitive flexible joints for support, the interference torque is reduced. Therefore, this type of gyroscope has a smaller volume, shorter start-up time, and greatly improved accuracy compared to the frame gyroscope. However, the high cost and complex manufacturing of dynamically tuned gyroscopes are their disadvantages, especially the flexible joints are very fragile and prone to breakage during vibration, resulting in damage to the gyroscope; If the stiffness of the flexible joint is increased, the accuracy will greatly decrease. This is the fatal weakness that limits its widespread application in petroleum instruments. There are factories in China that use dynamically tuned gyroscopes to develop gyroscope inclinometers. From the current application situation, the results are not ideal, mainly because the problem of gyroscope vulnerability has not been solved. The rotor support element of the dynamically tuned gyroscope uses flexible support instead of ball support in the frame gyroscope. The gyroscope body consists of a rotor, flexible joint, sensor, torque converter, and drive circuit. The structure is shown in Figure 2. The flexible joint consists of three rings: upper, middle, and lower, which are the key components determining its working quality. Compared with the frame gyroscope, due to the improved structure of the rotor part and the use of rigid and sensitive flexible joints for support, the interference torque is reduced. Therefore, this type of gyroscope has a smaller volume, shorter start-up time, and greatly improved accuracy compared to the frame gyroscope. However, the high cost and complex manufacturing of dynamically tuned gyroscopes are their disadvantages, especially the flexible joints are very fragile and prone to breakage during vibration, resulting in damage to the gyroscope; If the stiffness of the flexible joint is increased, the accuracy will greatly decrease. This is the fatal weakness that limits its widespread application in petroleum instruments. There are factories in China that use dynamically tuned gyroscopes to develop gyroscope inclinometers. From the current application situation, the results are not ideal, mainly because the problem of gyroscope vulnerability has not been solved.
Figure 2 Dynamic tuning gyroscope structure
The rotor of the liquid floating rate integration gyroscope is filled with a high-density, high viscosity suspension between the rotor and the housing, and the rotor is kept in a suspended state at an appropriate working temperature. The rotor and the housing are connected by an elastic balance spring. Its advantages are good vibration resistance, small volume, but limited by its suspension, long preparation time and large temperature drift. Generally, it should work at a constant temperature. Although liquid floating gyroscopes have relatively excellent anti vibration performance indicators, strictly speaking, this type of gyroscope is not suitable for use in gyroscope inclinometers. Due to the presence of suspension, excessive temperature differences in the working environment can cause significant changes in the density and viscosity of the suspension, and even loss of damping effect, directly leading to unforeseeable and significant changes in gyroscope accuracy, and even failure. If a precise temperature control circuit is installed, it will increase the volume of the instrument and is not suitable for high-temperature and high-pressure environments underground. The three types of mechanical gyroscopes mentioned above, when applied to petroleum instruments, are limited by their principles when considering the three major selection criteria of accuracy, anti vibration, and environmental temperature, and each has significant shortcomings. Optical gyroscopes can be used for gyroscope inclinometry. Common optical gyroscopes include fiber optic gyroscopes and laser gyroscopes. However, laser gyroscopes are not considered at this stage due to their large size. The following focuses on the application of fiber optic gyroscopes in inclinometers. Modern fiber optic gyroscopes have been developed based on the Sagnac theory. The key point of Sagnac theory is that when a beam of light travels in a circular channel, if the circular channel itself has a rotational speed, the time required for the light to travel along the direction of rotation of the channel is longer than the time required to travel along the opposite direction of rotation of the channel. That is to say, when the optical loop rotates, the optical path of the optical loop will change relative to the optical path of the loop at rest in different directions of advance. By utilizing this change in optical path length, if interference is generated between light traveling in different directions to measure the rotational speed of the loop, an interferometric fiber optic gyroscope can be manufactured. The basic optical components of fiber optic gyroscope include light source, coupler, polarizer, fiber coil, detector, etc. Fiber optic gyroscope components are mostly semiconductor devices that are connected to each other through plug-in connections and directly soldered onto printed circuit boards. The use of fiber optic gyroscopes in petroleum instruments overcomes almost all the disadvantages of mechanical gyroscopes, such as poor vibration resistance, magnetic field variations, multiple drift torque factors, and high susceptibility to environmental temperature during operation. Fiber optic gyroscope is a highly suitable azimuth sensor for gyroscope inclinometers. The important body defects of fiber optic gyroscope are the expensive cost of components and poor high-temperature resistance. And in order to ensure accuracy, more and more fiber turns are being used, resulting in a relatively large volume. The solution is to install an efficient insulation bottle externally to ensure that the maximum working environment temperature of the fiber optic gyroscope is below 80 ° C, which can basically meet the measurement needs of well depths within 4000 meters. Corresponding to the diameter limitation of the oil well, by changing the fiber winding method, its diameter can be effectively reduced to meet the requirements for placement in the drill pipe. The AgileLight IM series fiber optic gyroscope, developed in collaboration between Wuxi Huilian Technology Co., Ltd. and Peking University, is specifically customized for oil well inclinometer measurement. The gyroscope has an outer diameter of only 32mm, a range of ± 4 °, zero bias of 0.5 °/hr (0.2 °/hr under thermal balance), a scaling factor of 0.000125, and a bandwidth of 10Hz. Resistance to impact of 100g, operating temperature range of -40 ° C to+75 ° C, lifespan of 55000 hours. There are no special environmental requirements during transportation and use, making it very suitable for use in inclinometers.
Composition and principle of gyroscope inclinometer
The inclinometer mainly consists of a surface part and a downhole part, as shown in Figure 3, which are connected by logging cables.
Figure 3 Structural diagram of inclinometer
The ground part mainly includes signal receiving and decoding circuits, depth display, ground power supply, and computers.
The function of the signal receiving and decoding circuit is to receive signals sent from underground to the surface, decode them, and then forward them to the surface computer for processing.
The depth display part receives the photoelectric pulse signal from the winch control system, converts it into a depth value, and displays it.
The function of the ground power supply is to convert AC power into DC power, which is used for underground sensors and circuit components. It is assembled with signal receiving and decoding circuits, as well as depth display, to form a ground control box.
The function of the ground computer is to calculate the spatial orientation of the drilling position where the instrument is located, including the top angle, azimuth angle, and tool face angle, based on the gyroscope and accelerometer signal values sent to the ground underground. At the same time, it sends control instructions to perform different operations on the underground instrument.
Underground section
The underground part includes inertial components composed of fiber optic gyroscope and accelerometer sensors, motors, underground secondary power supply, data acquisition and encoding circuits, and gyroscope and accelerometer secondary circuits.
The inertial body is the core component of the entire instrument, consisting of two quartz flexible accelerometers and one single axis fiber optic gyroscope (dual axis gyroscope can also be used, but the cost and price will be doubled, so the motor only needs to rotate 180 ° once. Using a single axis gyroscope requires the motor to rotate four times, each time by 90 °). The gyroscope and accelerometer are arranged in a strapdown mechanical configuration, directly mounted on an inertial body with precise positioning reference to form an inertial body component. Two accelerometers are fixed on two orthogonal planes of the inertial body, and the output axes of the accelerometers and gyroscopes are perpendicular to the axis of the inertial body component.
The function of the motor is to make the inertial component perform four measurements with a difference of 90 degrees during measurement, obtain ωx and ωy , and eliminate the fixed zero bias error of the inertial component.
The secondary circuit of the sensor includes the gyroscope system and the secondary circuit of the accelerometer.
The signal acquisition and encoding circuit completes the data acquisition, control, and communication between the downhole system and the surface system for gyroscopes and accelerometers. After receiving commands from the ground, it decodes them and completes its respective functions.
The function of the underground secondary power supply is to convert the high-voltage DC power supplied from the well into low-voltage DC power, providing working voltage for the underground system.
Measuring Principle
The measurement mode of the fiber optic gyroscope drilling inclinometer is to lower the inclinometer to a predetermined position to keep it stable. The fiber optic gyroscope and accelerometer of the inclinometer respectively sense the acceleration of the earth's gravity, and calculate the azimuth angle A, top angle I, and tool face angle T of the drilling hole at that position based on the output values of the gyroscope and accelerometer. This completes the measurement of a point, and then moves the inclinometer to another position to repeat the above actions before measuring that point. The calculation process for the angle I, azimuth angle A, and tool face angle T is as follows: using the coordinate system of the gyroscope drilling inclinometer, that is, the coordinate system of the measuring device, as the reference coordinate system, counterclockwise rotation is the forward direction, and the latitude where the gyroscope inclinometer is located is set as the center. The coordinate transformation situation is as follows: in the northeast sky of the geographic system 0XoYoZo, first rotate the angle A in the positive direction around 0Zo to 0XYZ, then rotate the angle I in the positive direction around OY to reach 0X ₂ Y ₂ Z2, and finally rotate around 0Z to reach 0XgY with the angle T; 2, which is the coordinate system of the gyroscope hole inclinometer. Among them, angle A is the azimuth angle, angle I is the vertex angle, and angle T is the tool face angle, as shown in Figure 4.
Conclusion:
The gyroscope inclinometer uses inertial navigation technology for drilling measurement. It utilizes the characteristics of strong autonomy, high navigation accuracy, and good reliability of inertial navigation devices. It adopts a strapdown north finding system composed of fiber optic gyroscope and accelerometer sensors. The gyroscope measures the component of the Earth's rotation rate, the accelerometer measures the component of the Earth's gravity acceleration, and then calculates the drilling top angle, azimuth angle, and tool face angle through relevant formulas. The gyroscope inclinometer has the following characteristics:
Small drift, high accuracy, and no correlation between data points eliminate the cumulative error of previous gyroscope inclinometers, effectively improving the accuracy of drilling trajectory measurement results.
The working process automatically seeks north without the need for initial orientation on the ground, and there is no need to calibrate north before and after measurement, eliminating human errors.
Not affected by geology and surrounding environment, resistant to magnetic interference, can be used in drill pipes, magnetic casings, and magnetic mining areas. The fiber optic gyroscope inclinometer overcomes all the shortcomings of previous gyroscope inclinometers. The AgileLight IM series gyroscope produced by Wuxi Huilian is specially customized for inclinometers, with high cost-effectiveness, easy use, and reliable quality. After testing by multiple user units, its performance fully meets the requirements and is an ideal choice for a wide range of inclinometer manufacturers.
Application of fiber optic gyroscope in gyroscope inclinometer
In the process of opening skylights in casing wells and retesting old wells, it is usually necessary to use a gyroscope inclinometer to measure the inclination azimuth value of the well. In areas with abnormal magnetic fields and well sections, due to the large measurement error of flux gates, gyroscope inclinometers also need to be used for azimuth measurement. In addition, in certain specific environments, such as high incidence periods of solar magnetic storms or situations where a third instrument is required for verification, gyroscopic inclinometers also have their unique role.
The azimuth measurement sensor in the gyroscope inclinometer is the gyroscope, and the gyroscope used in oil well measurement is developed by transplanting from the gyroscope in aircraft. Currently, most gyroscope inclinometer manufacturers are specialized in producing space navigation equipment. The gyroscope not only has a precise structure, high process requirements, and complex testing, but more importantly, it is necessary to establish a matrix equation for the gyroscope output signal for highly specialized and complex calculations. At the same time, it is necessary to compensate for the drift caused by interference force distance, temperature drift, and impact vibration, and perform multi-level correction of its principle error. This is also almost impossible for non professional factories to achieve in a short period of time.
The IM100 fiber optic gyroscope, developed in collaboration between Wuxi Huilian Information Technology Co., Ltd. and Peking University, is specially customized for oil well inclinometry. The gyroscope has an outer diameter of only 32mm, a range of ± 30 °, and a zero bias of 0.02 °/hr, and can fully autonomously search for north. With a lifespan of 55000 hours, there are no special environmental requirements during transportation and use. It has high cost-effectiveness, easy use, and reliable quality. After testing by multiple user units, its performance fully meets the requirements, making it an ideal choice for a large number of inclinometer manufacturers.
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