Abstract:Based on the ability of VLF electromagnetic waves passing through the stratum, the study is made on the impact of the earth to signals to evaluate the relationship between the frequency, power and signal passing ability, discuss the realization principles of signal localization in signal source, antenna, signal processing and filtering as well as the key technologies, select a reasonable way and carrier mechanism for underground-surface communication, build a simplified magnetic dipole sub-localization model to complete the orientation and depth determination. This paper summarizes the key programs of very low frequency electromagnetic waves localization technology to provide a new communication technology for in-hole signal transmission in drilling field, such as CBM horizontal well, horizontal butted hole, pilot hole of directional drilling and mine rescue.

Abstract:The influence of casing can not be ignored for evaluating the transmission effect of EM-MWD signal, and it is difficult to analyze this effect with mathematical models because of the casings extremely complicated effects. Therefore, modeling and stimulation of EM- MWD signal transmission in the casing were made by ANSYS finite element software to analyze the influence rule of casing on EM-MWD signal transmission in the aspects of ground current density and ground receiver voltage. The stimulation results show that the casing plays a guiding role to the signal when insulation nipple is out of the casing, and conversely, the casing has a shielding effect on the signal; low resistivity drilling fluid has a great influence on EM-MWD signal transmission in the casing.

Abstract:According to the requirements of the strength and MWD communication to the drill pipe for the directional drilling technology, center cable drill pipe is used to realize real-time MWD signal transmission; and the high strength pipe, special screw thread structure, friction welding technology are adopted to improve the tensile, compression, bending and torsional strength of pipe. The necessary solutions are introduced based on the existing problems in field operation. MWD examples in Dafosi mine, comb hole examples in Zhuxianzhuang mine and directional drilling examples in Hashatu mine respectively prove that the center cable drill pipe can meet the requirements of measuring communication and strength with the maximum hole depth of 1200m, the directional drilling with minimum bending radius of 54m and directional drilling in coal seam with inclined angle of 58.