Research On Vibration Measuring Device For Down-hole Near Bit Tool

Drilling engineering is a high investment and high-risk downhole project.Shock and vibration are the main causes of the failure of measurement while drilling system and drilling tools.It is necessary to study the near-bit vibration to solve the problem.However,in the drilling process,there is currently no technology available for high-speed communication of ground-downhole mass data.Therefore,the only feasible technical means is to measure,collect and record relevant parameters during At-bit drilling process and study downhole vibration by data playback.However,the harsh conditions of underground limit the realization of large capacity,fast acquisition and storage devices.In this regard,the main research content and stage achievements of this paper are as follows:1^st.Expanding the storage capacity as much as possible is the most effective measure to achieve high-capacity storage.To meet the requirements of high-temperature environment and fast storage in downhole applications,a high-temperature and high-speed memory was selected and subjected to high-temperature aging treatment.A memory array design was adopted,which resulted in a total storage capacity of 8Gb.Calculating 32 bytes per record,the total number of records can reach over 33 million.2^nd.By simplifying hardware circuit,using multi-channel sequential sampling,optimizing data recording structure,and combining with memory high-speed page writing technology,the data writing rate is improved.As a result,the system sampling and storage frequency can exceed1000Hz,and the signal sampling and storage information rate can reach more than 32000 bytes per second.This performance indicator is close to the downhole storage multi-Sense 2.0dynamics mapping system recently launched by Baker Hughes.3^rd.In order to record complete downhole information,the data storage scheduling problem with limited storage capacity is studied considering that drilling tools run for less than 240 hours each time.According to the characteristics of near-bit vibration information,the fuzzy classification method of data importance and the storage optimization strategy based on the idea of information entropy are proposed.Based on the 8Gb storage frame,this storage strategy can effectively record 250 hours of near-bit vibration measurements at a sampling frequency of at least 10Hz,and can store at least 6 hours of high-frequency sampling（sampling frequency of at least 1KHz）.Through circuit design,software development,and system integration,a prototype was made based on the principle and tested.High-temperature tests showed that the system can operate stably at a high temperature of 125 centigrade.Through multiple rounds of hydraulic drive experiments and tests that simulate actual drilling operations,the reliability of the system’s hardware and software was verified.The research results of this paper have engineering reference value for storage measurement devices in harsh downhole work environments.