Research On Forward Detection Method Based On Half Coil Principle

With the deepening of oil and gas exploration,drilling has developed from vertical wells to directional wells,cluster wells,and then to horizontal wells,well factories and other complex structural wells.Well type technology is constantly innovating,especially the emergence of cluster wells and well factories.Advanced geosteering drilling technology is needed to prevent well collisions,avoid obstacles,etc.,ensure that the wellbore trajectory is drilled along the expected trajectory,and ensure the best oil production capacity.In this paper,COMSOL software is used to establish the structure of the forward detection instrument based on the halfcoil system and the complex stratum model.The forward detection instruments with different structures are designed and completed.The structure,forward detection principle,instrument parameters and response characteristics of various strata detection based on the half-coil system are studied,which lays a theoretical foundation for the design and application of the forward detection instrument based on the half-coil system.The first part studies the principle of half-coil forward detection and its numerical calculation method of logging response.According to Maxwell ’s equations,the calculation formula of voltage receiving signal with forward lateral detection ability is derived,and a threedimensional numerical calculation model of logging response of half-coil instrument based on COMSOL software is established.The rationality of the model and the correctness of the calculation results are verified by comparison with the analytical solution.The second part studies the structure and parameter design of the half-coil forward detection instrument.The azimuth sensitivity and forward signal strength of three kinds of half-coil forward detection instrument structures are analyzed.An optimal forward detection structure is designed to increase the forward detection distance.The influence of working frequency and other parameters on the detection response characteristics of the instrument is studied,and the most suitable instrument parameters for forward detection are designed.The data show that in the vertical well,the forward detection ability is the strongest among the three instruments when the horizontal transmitting vertical receiving single transmitting double receiving structure on both sides and the receiving coils are reversed.When the working frequency is 100 k Hz,the signal intensity is the highest when the source distance of the coil system is 1.5m,and the forward remote detection of short source distance is realized.When the half-coil azimuth angle is0 °,the detection distance can reach 15 m,which is about 10 times of the transceiver spacing.The third part studies the response characteristics of half-coil forward detection in threelayer strata.Based on the forward detection structure of half-coil system,a three-layer formation model is established and verified.The important influence of formation conductivity contrast,borehole influence,intrusive layer,surrounding rock and formation dip angle on the received signal of half-coil is studied.The results show that under the same environmental conditions,the amplitude of the received signal of the whole half coil is twice higher than that of the whole coil.The greater the conductivity contrast,the more serious the borehole effect on the received signal.When the conductivity contrast of the surrounding rock is high and the thickness of the target layer is small,the influence on the received signal is the most significant.When the formation dip angle is between 0 ° and 90 °,the received signal of the drill collar will change significantly with the change of the formation dip angle.Among them,with the increase of the formation dip angle,the forward detection ability gradually weakens.