Signals Attenuation and Application of EM-MWD in China

In the course of drilling utilizes directional well and horizontal well, it is indispensable to master timely and exact geological guide information, and offering services for such complicated drilling is electromagnetic Measurement While Drilling (EM-MWD) which can measure guide data of drilling tool in the hole and formation data while drilling. This knowledge allows the directional driller to make appropriate mechanical corrections in drill string orientation that will allow the advancing drill bit to hit an intended subsurface target area. Based on electromagnetic field theory, the paper has studied the propagation particularity and attenuation regularity that the signals of electromagnetic wave for EM-MWD transmit in stratum. The paper also gives a brief introduction of the containing, the work principle and the main technology parameter of EM-MWD. To check up the performance of EM-MWD, the field test of 5 wells were carried out in Shengli Oilfield and Liaohe Oilfield. Numerical simulation results indicate the signal attenuation will be added with the decrease of the stratum resistibility. In the frequency range from 1 to 10 Hz the stratum absorptivity is tiny and does not add noticeably with the increase of the electromagnetic wave frequency and the decrease of the stratum resistibility. In the frequency range from 1 to 10000 Hz the stratum absorptivity does not increase noticeably with the decrease of the dielectric constant of the stratum. Field test demonstrate that EM-MWD receives successfully signal emitted from depth underground 1600 meters in Shengli oilfield and 2400 meters in Liaohe oilfield. Our results indicate that numerical simulation methods are comparable to field test.