Research on transmitting technology of a LWD resistivity imaging tool with annular solenoid excitation
JIA Jiang, KE Shizhen, ZHANG Bing, KANG Zhengming, CHEN Shichang, LIANG Chaowei
1 State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing, 102249, China 2 College of Geophysics, China University of Petroleum-Beijing, Beijing, 102249, China
A series of developments has been made on annular solenoid excitation. This is an excitation method that is more suitable for a resistivity imaging logging-while-drilling (LWD) tool than the traditional electrode-type and coil-type focusing excitation. Experiments were carried out to investigate the electrical characteristics of an annular solenoid. The results show that an annular solenoid excitation device can be equivalent to a sort of multiple turn to single turn non-ideal transformer. The voltage ratio is equal to the turn ratio of the primary-to-secondary windings but the current ratio and power ratio are nonlinear and there is an upper output power limit. The annular solenoid was optimized based on electromagnetic theory. An annular solenoid excitation device was fabricated by using enameled copper wire around a magnetic core of iron-based nanocrystalline material with a cross-sectional area of 1 cm2 for 100 turns and the excitation frequency was set to 1 kHz. The signal transmitting circuit is designed based on a DSP (digital signal processor) and a DDS (direct digital frequency synthesizer) to generate an alternating voltage with adjustable frequency and amplitude. The physics simulation experiment was carried out with resistances instead of the formation and drilling mud. A non-magnetic steel cylinder was used to replace the drill collar and a button electrode with an annular solenoid was designed as the receiving device. The results show that there is a high correlation between the measured resistance mimicking the formation and the real resistance. It proves that the signal transmitting circuit and the annular solenoid excitation device are suitable for a LWD resistivity imaging tool and the corresponding results are a useful reference for its further development.
annular solenoid; electrical specification; magnetic core; excitation conditions; signal transmitting circuit; physics simulation
JIA Jiang, KE Shizhen, ZHANG Bing, KANG Zhengming, CHEN Shichang, LIANG Chaowei. Research on transmitting technology of a LWD resistivity imaging tool with annular solenoid excitation. Petroleum Science Bulletin, 2018, 04: 399-409