A cross-wound push-pull downhole three-component fiber optic seismometer

Abstract

The invention provides a cross-wound push-pull downhole three-component optical fiber seismometer, which belongs to the field of optical fiber interference measurement. It mainly includes a signal processing system, a signal acquisition system, a vector accelerometer, a communication cable and an optical cable. Two sensing units with the same structure are orthogonally stacked to form a three-dimensional vector sensing probe. The outside is protected by an outer cylinder and a sealed end cap. The sensitive optical fiber adopts the form of external winding, and the main structural components are enclosed inside the sensitive optical fiber. At the same time, the sensitive optical fiber is cross-wound between the two leaf spring fixing blocks and the two fiber winding columns, and together with the mass block forms a push-pull structure, wherein the mass block directly stretches the sensitive fiber through the fiber winding columns at both ends. The advantages of the device are that the vibration direction of the mass block is good, the lateral crosstalk is low, high strain transfer efficiency and sensitivity can be achieved, and the structure is compact, which can meet the measurement requirements in narrow spaces, and is especially suitable for deep well seismic observation.

Description

technical field [0001] The invention relates to a cross-winding push-pull type downhole three-component optical fiber seismometer, and the field of optical fiber interference measurement. Background technique [0002] The earth is a very active sphere. The continental plates move every moment. Earthquakes occur almost every day. Among them, there are more than 100 destructive earthquakes every year, causing countless disasters to the world. Since the 20th century, more than 30% of the world's destructive earthquakes have occurred in my country, and 70% of them are shallow earthquakes, which are highly destructive. More than 80% of my country's provinces have been affected by earthquake disasters. A total of 660,000 people have lost their lives due to the earthquake, and the number of injured has reached one million. Hundreds of millions of people have been affected. The earthquake has caused huge losses to my country's economy and people's livelihood. Therefore, it is immin...

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Problems solved by technology

[0005] In 2016, Oleg T. Kamenev et al. proposed a highly sensitive and low-noise fiber-optic seismometer based on Mach-Zehnder interferometer (Kamenev O T, Kulchin Y N, Petrov Y S, et al. Fiber-optics seismometer on the basis of Mach -Zehnder interferometer[J].Sensors and Actuators A-physical,2016:133-137.), in the seismometer sensing structure, multiple turns of sensitive optical fiber are wound between two cylinders, one of which is fixed horizontally as the base The other cylinder is suspended in the air as a mass, and the suspended mass is used to sense the seismic signal and transmit it to the sensitive optical fiber to cause the sensitive optical fiber to stretch or shrink. Although in the range of 1-20Hz, up to 6.1×10 3 V / g sensitivity, but the resonance frequency of the structure is low, only about 60Hz, and only one-dimensional seismic signals in the vertical direction can be measured, and three-dimensional expansion cannot be performed, which limits the application of the structure

[0006] The present invention provides a cross-winding push-pull downhole three-component fiber optic seismometer. Its design concept is: in view of the sensing principle and structural characteristics of traditional mandrel or disk fiber optic accelerometers, its strain transfer model is generally mass Indirect strain transfer from block to elastomer to sensitive fiber, resulting in inefficient transfer

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