Study On Spiral Cable Structure In The Distributed Seismic Detection System

With the deepening of the development of oil and gas resources, the difficulty of oil and gas resources exploration in the world is increasing, at present, the level of exploration and development of our country is still not perfect, there exists many defects in the actual exploration process. In recent years, with the development of optical fiber sensing technology, fiber exploration technology caused widespread concern in the oil and gas workers. Exploration technology based on the optical fiber sensing technology with optical fiber as transmission and sensing medium, optical fiber has the characters of resistance to electromagnetic interference, small volume, light weight, corrosion resistance and high temperature resistant, it can adapt to harsh working conditions of the seismic exploration.Fiber distributed seismic detection system based on phase sensitive optical time domain reflectometry (Φ-OTDR) technique, which not only has the advantages of anti-electromagnetic interference, corrosion resistance, but also has high sensitivity, distributed measurement of long distance and other important features. Compared to the traditional detection ways, fiber distributed seismometer system can complete the data acquisition of thousands of points along fiber length simultaneously, and traditional detection systems need to cascade multiple detectors, and upgrade detectors for multiple times to complete data acquisition. At the same time, the fiber distributed seismic detection system has the adjustable spatial resolution, seismic exploration of the channel density can be set according to the needs of the application. This makes it have wide application space in oil and gas exploration. The fiber distributed seismic detection system is successfully applied in oil and gas exploration will become a breakthrough to the traditional exploration technology, but also of great significance to China’s oil exploration.This paper in view of the two aspects of system research and engineering application of fiber distributed seismic detection system, mainly to complete the following work:1) Introduced the principle of Rayleigh scattering phenomena and Φ-OTDR techniques, and then analyzes the main performance index of optical time-domain reflectometer system, finally conduct a study of the structure of the optical system, a light source linewidth and frequency drift and photoelectric detection methods.2) Introduced common cable structure and classification, and according to the combination of cable structure and application requirements, proposed a novel spiral cable structure, through theoretical analysis, the fiber helix angle is determined to 33° We carried the fiber spiral simulation experiments based on distributed detection system showed that the spiral cable relative to the straight cable, has better signal response and then completed the design of the structure. Finally, suggestions are put forward for the practical application of optical fiber cable.3) Optical system were builded and optimizated, and then we carried out the earthquake detection test and evaluated the system performance. According the test,we found that signal of fiber distributed seismic detection system are in good agreement with the signal of traditional detector in time domain. On the basis of this, downhole seismic detection field test and surface seismic detection field test was carried out, compared with the traditional electronic detector and optical fiber detector data, and validated the feasibility of the application of distributed detection system in seismic exploration.