Edinburgh Napier University

  To carry out remedial work in oil wells through the production tubing string, a method using a continuous length of steel tubing or coiled tubing is used. Furthermore, coiled tubing can also be used for drilling and extending existing wells. In horizontal wells, substantial frictional forces are generated which resist the motion of the tubular drill pipe as it is pushed into the well. As the penetration increases, the frictional forces arising from the contact of the tubing with the inner casing wall increase too, and the tubular pipe buckles. The buckling is initially sinusoidal but eventually transforms into helical. At this point the force required to push the tubular drill pipe rises dramatically, and the maximum penetration is then rapidly reached. To date, scale model experimental studies on horizontal wells have not reproduced the actual conditions occurring in the wells. A new experimental rig has been designed that allows for the simulation and observation of all significant parameters. An analytical model has also been developed which is in excellent agreement with the experimental data. Governing modelling parameters have been identified which suggest ways to increase the penetration of tubular drill pipes in production oil wells.