Hydraulic System Design Of Downhole Device For Sampling And Expelling Drilling Fluid

During the exploitation of oil and gas,it is of vital importance to discover and evaluate oil and gas reservoirs.Gas-logging technology can help in gaining more downhole information through detecting the gas in drilling fluid.As the drilling fluid will be processed and examined after it's taken to the ground,there are some problems such as information lagging and difficulty in quantitative analysis.To solve the problems,oil-field service companies at home and abroad started to carry out the relevant research of downhole Gas-logging technology,aim to develop a gas tester while drilling that can quickly determine the existence of oil & gas and the type of oil & gas under several thousand meters of the well.In order to detect the information of oil & gas,the drilling fluid need to be pumped to the internal detecting system,and then be discharged into wellbore after the detection.Therefore,the study of the downhole device for sampling and expelling has important significance and engineering application background.Firstly,the research and application of technology for sampling and expelling at home and abroad were analyzed,the technical index and functional requirements of the device were introduced.Then,according to the characteristics of the limited radial dimension and larger axial size of the device,the scheme of integral structure layout was proposed,the structural parameters of the outer tube and inter tuber were calculated and verified.With the idea of modular design,the device was divided into several modules.Secondly,the influence of downhole environment on the device was analyzed.For the key problems such as the high pressure of wellbore,the difficulty in sealing and the fragility of major parts toward pressure,the scheme that appling the pressure compensation technique to the closed downhole hydraulic system was proposed.Through studying the different compensation states in pressure compensation process,the compensation volume of pressure compensation device was calculated,the structure was designed.Thirdly,the implementation approach of downhole hydraulic system for sampling and expelling was studied,the major parameters of hydraulic system were designed.Then,according to the downhole characteristics of high temperature,narrow space,strong corrosion,the major parts in system were selected,the structure of the main modules of system was designed in an integrated manner.Finally,the simulation model of downhole hydraulic system was established by the AMESim and Matlab/Simulink software,and the process such as sampling,decompression,and expelling was simulated.In addition,the principle experiment of hydraulic system was carried out,in order to further verify the feasibility of the design of downhole hydraulic system.