Study On Lateral Resistivity Logging-While-Drilling Method In Oil-Based Drilling Fluid

Resistivity logging is an important technique of identifying and estimating reservoirs.Lateral resistivity logging-while-drilling(LWD)is an important resistivity logging technique,which has the advantages of high measurement accuracy,wide measurement range and large detection depth.It is mainly used in the conductive water-based drilling fluid environment.Compared with water-based drilling fluid,oil-based drilling fluid can improve drilling efficiency and decrease operation risks,so it has received extensive attention in recent years.However,the electrical insulation characteristic of the oil-based drilling fluid will block the low frequency measurement path,which makes the conventional water-based lateral resistivity LWD method ineffective.Therefore,it is of great significance to undertake the research works concerning the lateral resistivity LWD technique which is suitable for oil-based drilling fluid.In this dissertation,the application of an oil-based lateral resistivity LWD method is studied,which provides a good reference to overcome the electrical insulation characteristic of the oil-based drilling fluid.The main work and innovation points are listed as follows:(1)To find the solution to the electrical insulation characteristic of the oil-based drilling fluid,this dissertation studies an oil-based lateral resistivity LWD method by combining the capacitively coupled contactless conductivity detection(C4D)technique and the inductive coupling principle.On the one hand,the C4D technique is introduced to overcome the electrical insulation of the oil-based drilling fluid and form an effective AC measurement path.On the other hand,the inductive coupling principle is used to generate the excitation source of the AC measurement path by a stable induced voltage.(2)Based on the new logging method,a new lateral resistivity LWD logging instrument is designed and the simulation study of the logging instrument is conducted.The simulation results show that the designed logging instrument has good resistivity measurement accuracy,deep detection depth and high vertical resolution,which verifies the feasibility of the new logging method.(3)The prototype of the lateral resistivity LWD logging instrument is designed,which mainly includes the sensor and the hardware circuit.Based on the designed hardware circuit,resistance box experiments are carried out.The experimental results show that the hardware circuit has good resistance measurement accuracy.(4)An experimental well is established to simulate the real formation with sandstone,and several patterns are specially designed on the wellbore of the experimental well to simulate the cracks and scratches existed in the formation.Based on the prototype of the lateral resistivity LWD logging instrument and the experimental well,an experimental setup is developed.With the developed experimental setup,the well logging experiments are carried out.Experimental results show that the designed logging instrument can accurately detect the patterns on the wellbore of the experimental well,which further verifies the feasibility of the new logging method and the effectiveness of the logging instrument.