The New Optical Detector, In The Oil And Gas Exploration

With the increasing demand to petroleum and natural gas, the new technology of geophysical exploration has been continuously developed. For the time being in our country, most oilfields that are buried shallowly or have simple geological structure have already been found. However, the traditional geophone is unable to fulfill the requirement of modern seismic exploration with high-resolution and little distorted degree. To the end of exploring the oilfields that are located at deeper level under the earth surface and/or have complicated geological structure, we need to develop new technology of geophysical exploration together with new types of geophones. In recent years, many countries are developing new-type geophones, and the scientific research institution in China has also made notable progress in this area.In this thesis, we first present an introduction and a review of the fiber Bragg grating and the applications of fiber Bragg grating in communication and sensing, respectively. Secondly we discuss the characteristics of reflection wave that is detected by the geophone in geological exploration. We also present an overview of the existing geophones that are being used and/or developed in the world. We then introduce the concept and the propagation theory of the seismic wave, and carry out analysis of the compensation method for the amplitude of reflection wave.Based on discussions above, to improve the defects of the traditional geophone such as low precision and poor sensitivity, we collaborate with scientists and technologists from Shengli Oilfield for the development of the optic seismic geophone. This geophone utilizes the fiber Bragg grating as the sensitive element, and has many advantages such as high precision, wide dynamic range, resist to electromagnetic interfering.Finally, in order to examine the performance of the fiber Bragg grating geophone system, we carry out in-situ experiments via comparing with the traditional 20DX type geophone. We employ frequency-spectral analysis method to study the signal characteristics such as amplitude, frequency, and energy that cannot be seen clearly intime-domain analysis. The results indicate that the fiber Bragg grating geophone designed in this study has characteristic of high-sensitivity and high-resolution compared to the traditional geophones. The primary experimental results shows that the dynamic range of the fiber Bragg grating geophone can reach about 80dB, which is much better than the 60 dB dynamic range of the traditional geophones.