New Method Of Lateral Resistivity Logging-While-Drilling In Oil-based Drilling Fluid

Well logging is the general term of the engineering technology used to solve geological and engineering problems in the process of exploration and exploitation of the underground mineral resources,such as oil,gas,coal and metal.It monitors the physical parameters of down-hole formation and technological condition of borehole by various instruments.Among all formation parameters,resistivity is a key one reflecting formation characteristics,such as lithology and petroliferous feature.As an important technique of resistivity logging,lateral resistivity logging-while-drilling(LWD)has been widely used in petroleum exploration and exploitation.However,conventional lateral resistivity LWD can only be applied in conductive water-based drilling fluid.In oil-based drilling liquid,nonconductive drilling liquid insulates the logging instrument from the measured formation and make the measurement failed.As a result,it is of significance importance to study on the lateral resistivity LWD suitable for oil-based drilling liquid condition.Combining the principle of the capacitively coupled contactless conductivity detection(C4D)technique and the inductive coupling principle,this thesis studys on a new lateral resistivity LWD method in oil-based drilling liquid.The main works and innovations of this thesis are as follows:(1)A new lateral resistivity LWD method is proposed based on the principle of the C4D technique and the inductive coupling principle.This method overco1es the influence of the nonconductive oil-based drilling liquid on measurement by the capacitive coupling principle of the C4D technique.The excitation source of the AC measurement circuit is developed on the basis of the inductive coupling principle.Then,the measurement of formation resistivity in oil-based drilling liquid is implemented with the built AC measurement circuit.(2)A relative well logging model is established for the new proposed lateral resistivity LWD method.This model is a series AC measurement path consists of the excitation source(developed by the inductive coupling principle),two coupling capacitance(one is formed by the drilling collar above the helical excitation coil and the borehole through oil-based drilling liquid,another is formed by the annular detection electrode beneath the helical excitation coil and the borehole through oil-based drilling liquid,respectively)and the measured formation resistivity.(3)To verify the effectiveness of the established model,a simulation model is developed by the COMSOL Multiphysics simulation software according to the proposed method and model.The effectiveness of the equivalent circuit model of the lateral resistivity LWD logging method is verified.In addition,the mapping relationship between the formation resistance and resistivity is obtained.(4)According to size of the actual drill collar(6.75"),a lateral resistivity LWD prototype is developed,including a sensor and its signal detection and processing system.The sensor is designed and developed on the basis of the new proposed resistivity measurement method and the corresponding model.The output current signal of the sensor is amplified and converted to a voltage signal by the signal detection and processing system.Then,the voltage signal is collected and sampled by NI data acquisition instrument.Finally,the digital phase sensitive demodulation(DPSD)technique is applied to implement the detection of the formation resistivity.(5)A simulated logging experimental device/system is designed based on the lateral resistivity LWD prototype,including a logging prototype,a simulated formation,a simulated borehole and an experimental platform.And further experiment is undertaken to verify the feasibility of the proposed new method and the effectiveness of the developed prototype.