| With the increase in horizontal wells and highly deviated wells, conventional cable logging technology can not satisfy the needs of the oil industry. Logging While Drilling(LWD) has become one of the most popular developments because of the high accuracy of measurement, timely and accurate and objective measurement information. This dissertation takes along with the TRIM induction resistivity tool (a tool used to measurement while drilling) as an object, uses COMSOL Multiphysics finite element software to study TRIM’s method and theory, develops the three dimensional numerical calculus program of logging response of TRIM. The response characteristics of TRIM without drill collar and with drill collar are calculated and analyzed by the program. Results provide the theoretical basis for tool calibration, tool design, logging data processing and analysis. The contents include the follow three topics.The first is the study of three-dimensional finite element analysis method of TRIM. Firstly, analytical expression of electromagnetic fields generated by magnetic dipole in uniform formation is derived in cartesian coordinate system. The expression used to validate the effectiveness of three-dimensional numerical calculation program. Secondly, beginning from the Maxwell equation, the electric and magnetic fields equations used in COMSOL software is derived. Then the paper focuses on the study that the electromagnetic response computational problems of three-dimensional complex model containing emission sources, V-shaped element, drill collar, the water eye that conducts the drilling fluid from surface to the drilling bit and infinite formation is calculated by the COMSOL. The paper solve serval problems, such as meshing the model reasonably, treatment of eccentric emission sources of TRIM, calculation of the received voltage and the apparent conductivity, display and calculation of electric field, magnetic field and current in the electromagnetic fields. These are basis for the analysis and calculation of the response characteristics of TRIM in complex model.Secondly, the response characteristics of TRIM in uniform formation are calculated and analyzed. The response characteristics without drill collar and with drill collar are calculated, analyzed and contrasted. The results show that the drill collar effect on the logging response approximates a fixed value, corresponding the directly coupling signal. When subtracting the fixed value, the apparent conductivity after calibration is same to without drill collars, which is laid a theoretical foundation for the practical application of TRIM. The paper calculates the measurement error generated by using the finite size of bucket to calibrate the measured voltage of TRIM. It can be used to remove the calibration error. The effects (transmitting frequency, V-shaped element opening size, eccentricity change) on logging response are analyzed. When the frequency is20kHz, the V-shaped element opening size is60°, the eccentric change is0.05m, apparent conductivity is closest to the true formation conductivity, which shows the current design of the instrument is reasonable.Finally, the response characteristics of TRIM in inhomogeneous formation are computed and analyzed. It considers several effects factor that include the borehole (borehole diameter and mud conductivity), invasion (invasion depth and invasive conductivity) and shoulder (layer thickness and shoulder conductivity). When the mud conductivity and formation conductivity ratio is less than10, borehole has little effect on the logging response, which shows TRIM can be suitable for the different borehole environments. When the invasion radius is less than0.4m, invasion and formation conductivity contrast is less than10, logging response is little affected by the invasion. When the thickness is greater than2m, the great mass of formation conductivity is read, the vertical resolution thickness of TRIM is greater than2m. These results show the quantitative detection characteristics of TRIM. |
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