Study on the FOG-based well-trajectory-logging tool

The commonly used technology in well-trajectory logging, for both the oil and the gas well, is the magnetometer. However, it cannot work well in the magnetic-interfered or nonmagnetic environment, such as in a cased well or an iron mine. This paper presents a new trajectory-logging tool with a small diameter. Configured by a three-axis FOG unit and three quartz accelerometers, the logging tool allows for continuous attitude and trajectory measurement. High-temperature-caused accuracy degradation is the major error source for the underground environment. To diminish the thermal-related error, a flask stuffed with thermal-insulation material was embedded in the tool body; meanwhile, a wavelet neural network was used for identification of and compensation for the temperature drift. The system configuration, trajectory-resolution algorithm, and temperature-compensation algorithm are presented in this paper. Testing results show that the inclination accuracy is better than +/-0.1 degrees, with a range of 0 to 180 degrees, and the azimuth accuracy is better than +/-2 degrees, with a range of 0 to 360 degrees. The new logging tool resolves continuous trajectory-measurement problems in a magnetic-interfered or a nonmagnetic environment. Moreover, the capability of all-attitude measuring facilitates horizontal-well logging. Therefore, broad applications and good marketing could be anticipated for this new logging tool.