Magnetization influence analysis of the casing and drill pipe in shale gas dual horizontal well Rotating Magnet Ranging System drilling process

摘要

Rotating Magnet Ranging System (RMRS) is one of the core guiding technologies for shale gas extraction, and its magnetic measurement data will inevitably be affected by the downhole magnetic objects in the target magnetic field. The casing and drill pipe, which are apt to be magnetized by the magnetic sub, are major influencing factors of the measurement results. In order to study the influence comprehensively, a dual horizontal well RMRS drilling model is established. Based on static magnetic dipole theory, the magnetic field distribution equation of the low‐rotational magnetic sub is deduced and characterized. Firstly, the casing and drill pipe were segmented into ring, layer, and block volume elements. Then according to the dynamic magnetic dipole field distribution equation, the magnetic field strength of the magnetic source at the volume element (equivalent magnetic dipole) and the sensor was calculated, as well as the magnetic strength of independent magnetization field and superposition magnetization field of casing and drill pipe at the sensor position. Finally, the effectiveness of the numerical method results was verified by outdoor experiments, and the shielding effect of the static magnetic shielding on the external magnetic field of casing was preliminarily analyzed. The research results indicate that the magnetic sub has a strong magnetization effect on the casing and drill pipe. The magnetization field of the casing is about 2.39 times stronger than that of the drill pipe, and they will seriously affect the sensor measurement data. When the well spacing is small, the magnetization field waveform will be distorted. With the increase of the well spacing d, the waveform gradually changes sinusoidally, the fluctuation period of the magnetization field also gradually becomes twice (d??1.5?m) that of the magnetic source, and the peak value of the magnetization field decreases exponentially. A preliminary analysis of the magnetic shielding of casing revealed that the magnetic shielding would cause great attenuation to the strength of the magnetic source. The numerical simulation proposed in this paper provides a theoretical basis for the error analysis of RMRS, which is of great significance for measurement correction and accuracy improvement.