| The overall goal of oil well logging service is to improve service quality and reduce service cost.In order to improve the wellbore quality,it is necessary to obtain the directional data,stratigraphic characteristics and drilling parameters to ensure the drill bits stay in the target layer in the process of measuring the designer wells and high-difficult horizontal wells.Such information should be transmitted to the ground without interrupting the normal drilling operation to guide the on-site construction.With the increasing number of measurement parameters,great efforts should be put into developing wireless measurement while drilling(MWD)and logging while drilling(LWD)technology.Drilling fluid mud pulse transmission is currently the most mature and widely used technology in wireless transmission mode.However,there are still some problems that the pressure signal is weak,the signal transmission distance is short,corrosion of the core mechanical parts are esay to erosion in practical applications.The strength of the signal source determines the downhole data transmission rate and transmission distance.The signal strength should be increased in order to improve the signal transmission rate,ensure accurate information transmission and improve the transmission distance.The objective of the paper is to improve the signal strength of positive pulse during the measurement while drilling process.Based on positive Pulse Measurement-While-Drilling(PP-MWD),the generation process and transmission behavior of positive pressure signal has been analyzed to ascertain the important parameters effecting signal strength and transmission distance.The overall design scheme of PP-MWD based on theoretical analysis and numerical calculation is put forward and verified experimentally.Some progress and achievements have been made in the mechanism of pressure signal generation,signal strength erosion and other aspects.The major results and conclusions are as follows:Section 1 is the theory of signal generation and its influencing factor:The generation of pressure signal is the same as the process of water hammer.The theory of water hammer is applied to derived the velocity equation of water hammer.The results show that the velocity of water hammer decreases as the drilling fluid density and the solid content and gas content of drilling fluid increase.Section 2 is design and optimization for rotary valve:The pressure signals is stable and reliable when the rotor blades are design as fan-shaped structures.The strength of the pressure signal is related to the drilling fluid flow,axial clearance,stator skew characteristics and the skew angle.The signal strength can be enhanced by increasing the flow rate of the drilling fluid and reducing the axial clearance.When the stator unilateral skew angle is ?/10,the signal strength is increased without causing the excessive local drilling fluid flow rate.Section 3 is analysis of mechanical properties of the rotor in rotary valve:It is very complicate for the mechanical properties of rotor.The bidirectional axial force should be considered when the rotor designed and installed.Section 4 is analysis of erosion characteristics:the erosion of the valve assembly basin is severe.The main erosion site is in the stator skew side of the downstream rotor basin.The erosion in the circumferential direction is evenly distributed.The wear-resistant sets should be added to improve the erosion resistance in the drilling field.Section 5 is the scheme of system design:The application of functional modules in design shall be in accordance with the requirements of function.The overall design should consider the power transmission,static seal,dynamic seal,pressure balance and other issues.Section 6 is the field tests:The strength of the signal are analyzed at different flow areas,the axial clearance,the drilling fluid flow,the transmission distance and the signal frequency.There is a high level of agreement between the theoretical predictions and the experimental results,which verify the reliability of the theoretical research.Finally,it summarizes the research results of this paper and puts forward the future research direction. |
PDF Full Text Request