Study On Resistivity Logging-While-Drilling And Imaging Logging Method In Oil-Based Mud

Resistivity logging-while-drilling(LWD)is an important technique to identify and evaluate reservoirs.Resistivity imaging logging technology is a downhole visualization technology that can analyze and evaluate fracture systems and help improve the accuracy of logging data.It has received extensive attention in recent years.Traditional resistivity imaging logging technology is difficult to achieve imaging while drilling,and there are problems that the resolution of imaging results is limited by the electrode size,and it is difficult to balance the imaging resolution and anti-interference capability of system.In addition,as oil-based drilling fluids are used widely for their better performance,the electrical insulation of the oil-based drilling fluid makes the traditional electrical logging methods ineffective.Therefore,it is of great significance to develop a resistivity imaging while drilling technology that has high accuracy and can overcome the limitation of the resolution of imaging results on the electrode size.In this dissertation,the research of oil-based resistivity logging-while-drilling and imaging methods has been carried out,which provides a new idea for solving the problem of imaging resolution and anti-interference capability of system in traditional resistivity imaging logging technology.The main work and innovations of this dissertation are as follows:(1)In this dissertation,by combining the image reconstruction algorithm,the sensitive field is introduced into resistivity imaging logging to quantify the influence of the surrounding formation on the measurement results,ease the influence of the soft field effect of the electric field on the measurement,so as to improve the resolution of the imaging logging result without reducing the size of the electrode.Capacitive coupling logging while drilling technology is used to obtain formation resistivity information,so as to realize the resistivity imaging while drilling technology in the oil-based drilling fluid environment.(2)Based on the proposed new imaging logging method,a finite element simulation model of imaging logging formation is established.With the finite element simulation model,the sensitivity distribution is obtained,and simulation logging experiments are carried out according to the sensitivity distribution.The simulation experiment results show that the proposed new imaging logging method can effectively improve the resolution of imaging logging results,which verifies the effectiveness of the new imaging logging method.(3)A set of resistivity imaging while drilling prototype is designed and built,which mainly includes the sensor,a hardware control circuit and a host computer.The resistance measurement experiment was designed to verify the measurement reliability of the prototype,and it was analyzed whether the sampling rate of the prototype could meet the sampling speed requirements of the proposed new imaging logging method.The results show that the prototype designed and built can meet the requirements of the new imaging logging method.(4)The simulation logging experiment platform was designed and built.Sandstone is used to simulate the formation,and different patterns are designed on the wellbore to simulate cracks.A logging experiment was carried out using the simulation logging experiment platform and the resistivity imaging while drilling prototype.Experimental results show that the proposed new imaging logging method can effectively improve the resolution of imaging logging without reducing the size of the electrode,which further verifies the effectiveness and feasibility of the new method.