The Study On The Response Characteristics Of The Dual Induction Logging While Drilling

Formation resistivity is an important parameter to analyse the lithology of formation and evaluate the oil and gas. With the continuous development of oil and gas exploration, horizontal well and highly deviated well, the current cable logging technology becomes difficult. Logging While Drilling(LWD) technology becomes the trend of current logging field due to timely measurement, high accuracy and more reliable information. Dual induction logging while drilling is a new type of induction resistivity logging while drilling. It can meet the requirements of directional trajectory measurement and geosteering while combined with the MWD and natural gamma ray logging. The basic theory, the background influence in the homogeneous formation, the borehole environment effects in the non-homogeneous formation, the signal processing and the half-space response characteristic are studied in detailly in this thesis. Results provide the theoretical basis for tool design, tool calibration, logging data processing and logging interpretation. The contents include the follow four parts.The first part introduces the background influence of the dual induction logging while drilling in the homogeneous formation. The coil configuration and measuring principle is described. Then, the mathematic and physical model is established using COMSOL software. The influence on the response feature of LWD dual induction logging is computed and analyzed when the formation conductivity is changed. The effect mechanism of mental drill collar and high permeability magnetic core on the dual induction logging while drilling are revealed. The effect of drill collar conductivity on the deep induction is a little when the conductivity is greater than 107S/m, shallow induction can not be ignored. The influence of drill collar length on the response can be neglected and the apparent conductivity is approximately proportional to the drill collar radius. The effect of drill collar on the deep and shallow induction is a little when the formation conductivity is less than 1S/m. Reflector has changed the nonlinear influence of drill collar on the base value. The influence of the deep induction has a nonlinear decrease with the increase of the formation conductivity. But the shallow induction increases. The responses of the deep and shallow induction have a nonlinear increase with the increase of the relative magnetic core permeability. The signal intensity is boosted obviously when the relative magnetic core permeability is between 100 and 200. The ratio of response of the deep and shallow induction under the action of solid magnet core and hollow magnet core approximates a fixed value(1.2).The second part studies environment influences on the dual induction logging while drilling in the non-homogeneous formation. Environmental influences include borehole influence, shoulder effect and invasion effect. In the borehole influence, how the formation conductivity, mud electrical conductivity and borehole diameter changes effects the response characteristic is calculated and analysed. The results show that the deep and shallow induction is greatly influenced by the formation conductivity. The influence of mud conductivity is obvious only whne in the formation conductivity is small. The influence of borehole diameter is small only when the mud conductivity is less than 1S/m. The measurement signals of the deep and shallow induction increase nonlinearly with increase of shoulder conductivity, with increase of the radius of invasion. Only when shoulder conductivity and conductivity contrast are large, the tool closes to the target layer, the measurement signal of dual induction logging-while-drilling changes obviously. The greater the target layer thickness, the smaller absolute error, the smaller the shoulder effect.The third part investigates the signal processing methods of deep and shallow induction. Calculate the deep and shallow induction vertical response function based on geometry factor theory. Analysis skin effect,shoulder effects and resolution characteristics. Design nonlinear signal processing filter. Achieve the resolution match between deep and shallow induction. Results show that in one-dimensional formation simulation, deep and shallow induction curves have been significantly improved. Their resulution can nearly coincide. In two-dimensional formation simulations, due to the shoulder effet, the resolutions of deep and shallow induction decrease. The reading deviates from the true value. In the processing of the actual measurement data, the shoulder effect is eliminated significantly. Both resolutions of deep induction are improved. The deep and shallow inductio has same resolution.The fourth part discusses the response characteristic of the dual induction logging tool while drilling in a half-space. The response characteristic is computed and analyzed when the instrument slots opening direction, instrument height, ground conductivity is changed respectively. Results show that the half-space response of the different opening direction of instrument slots has a nonlinear change with the increase of the ground conductivity. The effect of half-space response on the tool slots downward opening direction is maxmium and the upward is minimal. The half-space response of the deep induction reaches the maximum near the 0.4m height when tool is above ground. The peak position does not change with the ground conductivity changes.