Study On Lateral Resistivity Logging-While-Drilling Method In Oil-based Drilling Fluid Based On C~4D Technique

In the process of oil exploration and exploitation,acquiring formation information in real time is of great significance.Logging while drilling(LWD)technique is an important tool to achieve this goal.Compared with the traditional logging techniques such as wire-line logging,LWD technique is playing a more and more important role in directional drilling field,due to its good real-time performance,high accuracy and low cost.However,traditional LWD resistivity logging techniques use DC or low frequency excitation and they are only suitable for water-based drilling fluid.Oil-based drilling fluid,which is widely used in recent years,will block DC and low frequency current paths due to its electrical insulation,making traditional LWD resistivity logging techniques no longer suitable.In this dissertation,capacitive coupling principle and inductive coupling principle were applied to LWD field on oil-based drilling fluid condition.A new lateral resistivity LWD method was studied.Capacitive coupling principle was used to overcome the influence of electrical insulation of oil-based drilling fluid and establish an AC logging model.Inductive coupling principle could provide an AC excitation source to the logging system and establish an AC measurement path.The simulation and experimental results showed that the new logging method was feasible.The work of this paper provided a new method for LWD logging in oil-based drilling fluid.The main works and innovation of this paper are as follows:(1)Capacitive coupling principle and inductive coupling principle were combined and applied to LWD field in oil-based drilling fluid.Based on COMSOL software platform,annular electrode and button electrode logging simulation model was established.The simulation experiments of lateral logging,azimuth logging and formation imaging were carried out under various working conditions.The simulation results verified that the proposed new logging method was feasible.(2)A set of LWD resistivity logging system was designed.The hardware of the logging system included:an AC excitation source,a spiral excitation coil,annular or azimuthal detection electrodes and a data acquisition&processing module.The feasibility of this sensor system was verified by using commercial instrumentation.Then,a dedicated hardware circuit of the data acquisition system was designed for the actual working environment.In addition,the short-circuit risk of the system caused by the formation was analyzed.The condition of the excitation coil when the measured impedance network changed was specially studied.The results showed that the short-circuit risk of the system caused by the formation did not exist.(3)A variety of simulated logging environment was built and a series of simulated logging experiments were carried out based on the designed logging system.Firstly,the annular electrode logging experiments were conducted under different formation conductivities.The experimental results showed that the system can measure the formation conductivity parameters.Then,azimuthal electrode logging experiments were carried out under the condition of simulated high and low resistivity target rocks and stratified formation respectively.The experimental results verified that the azimuthal logging system had certain azimuthal detection capability.Finally,the formation imaging experiments were carried out by using the button electrode.The experimental results showed that the button electrode logging system could implement formation imaging and measure the formation dip angle.