Drill string vibration analysis and pressurization scheme for medium-shallow horizontal wells

Medium and shallow oil and gas reservoirs are characterized by shallow buried depth, poor physical properties and low natural productivity, they are tight sandstone oil reservoirs and difficult to produce, they bring great challenges to horizontal well drilling. Among them, problems of drill string vibration, drag pressure and friction are urgent ones to be solved. Therefore, the simulation of drill string vibration and friction is very important. Here, taking the horizontal well in Ordos area as an example, based on the 3-D coupled vibration model, dynamic characteristics of drill string of two different well depth structures in Ordos area were described from 3 aspects of axial force, horizontal displacement of drill string and friction torque, and compared with those of medium-deep wells. In the process of using heavy weight drill pipe (HWDP) and hydraulic oscillator to solve the drag pressure problem, effects of number and size of HWDP, pulse force of hydraulic oscillator and installation position on dynamic characteristics and fatigue life of drill string were discussed. Results showed that compared with medium-deep horizontal wells, the WOB fluctuation of medium-shallow horizontal wells is only 1/8 of that of medium-deep wells, but the axial force fluctuation in oblique segment, especially, near neutral point is very large and reaches 20 kN, it is 1/3 of that of medium-deep wells, so drill string vibrations in oblique segment and near neutral point receive much attention; to solve the problem of supporting pressure, adding 10-12 or 18-20 ∅114 mm or ∅127 mm HWDPs at place from the end of vertical segment to 25°-35 ° deviation segment can not only ensure smaller WOB fluctuation and friction, but also ensure high fatigue life of drill string in oblique segment. The conclusion was applied in site. In addition, a hydraulic oscillator was used together to further reduce friction. It was recommended that the hydraulic oscillator should be installed at 40 m away from the drill bit, and the pulse force should be 21 kN. © 2020, Editorial Office of Journal of Vibration and Shock. All right reserved.