Experimental and numerical study of drill string dynamics in gas drilling of horizontal wells

Abstract

The combination of gas drilling and horizontal well has been considered as an effective technique for the exploitation of low permeability reservoirs to protect reservoir, enlarge drainage area and increase production. Given the currently inadequate understanding about drill string dynamic characteristics in gas drilling of horizontal wells, a theoretical model of drill string dynamics is established in this paper. The nonlinear dynamics equations are derived to study the motion state of drill string. Meanwhile, an experimental apparatus is developed according to similarity principle, and the kinetic characteristic of drill string is investigated based on the simulation experiment. Particular attention is focused on the lateral vibration which results from the impact and frictional interaction with wellbore constraint. The effect of weight on bit and rotary speed on drill string motion pattern is also discussed based on experimental results. Finally, the buckling and contact of drill string are analyzed through finite element simulation study. The results indicates that the contact force between wellbore and drill string is relatively large and helical buckling of drill string can be caused without the lubrication and damping effects of drilling fluid in gas drilling. The work presented in this paper can provide theoretical foundation and technological basis for drill string dynamics analysis and drilling parameter optimization in horizontal wells drilled with gas.