Research On Downhole Vibroseis Tools For Gas Drilling

Gas drilling is a kind of underbalanced drilling.Its main advantage is to reduce reservoir pollution,avoid drilling problems such as lost circulation,and to a large extent improve drilling speed and save drilling costs.However,when gas drilling horizontal or highly deviated wells,it is easy to occur because of the errors in formation information prediction and the inaccurate knowledge of the geological conditions ahead of the drill bit,which makes it impossible to predict the position of the water layer,the lithology of the formation to be drilled and the abnormal high pressure formation,which will increase the safety risk of drilling and even lead to drilling accidents.Using seismic while drilling technology,the formation before the bit can be well judged and identified,but the existing seismic while drilling method can not be directly applied to gas drilling.In this paper,the structure design,laboratory experiments and computer simulation of downhole vibroseis tools for gas drilling are studied.The main research results are as follows:(1)The radiation characteristics of the downhole impact source are analyzed.The feasibility of using vibration wave to measure rock interface distance is determined by using ultrasonic ranging experiment,and the vibration parameters of vibroseis are determined by simulation.(2)Combining with gas drilling conditions and relevant design specifications of drill collars,the structure of downhole vibroseis in gas drilling is designed,and the key parameters such as sleeve outer diameter,sleeve wall thickness and barrel inner and outer diameter are determined.(3)The main factors affecting the vibration frequency are determined through laboratory experiments,which proves that the vibration wave generated by the downhole vibroseis tool in gas drilling can meet the frequency required by the detection wave.(4)By using finite element simulation,the influence of the parameters of vibroseis on the motion characteristics of sliders is analyzed,which provides a basis for the design of vibroseis.This paper provides a new idea for the development of downhole vibroseis tools for gas drilling,and has a certain reference significance for the research of similar tools.