The Tapered Stabilizer is suited for formation which easily reduces diameter. When happen bit freezing accident, it can leave enough operating space for fishing job. Stabilizer is one of main drill tool assembly in hole guiding. During drilling in deviating and horizontal well, in view of workmanship, the outer diameter of the stabilizer is required to be equal or 1~2mm less than drill bit so that too small clearance between borehole wall and stabilizer usually causes stabilizer to be easily stuck during tripping out of hole. However, variable diameter stabilizer solves the problem which common stabilizer can not solves. During drilling in directional well, by use of differential pressure at nozzle produced by circulation of fluid among inside and outside of drill string, stabilizer stretch out supporting head to reach full hole so that stabilizer equipped with different drill tools to increase or angle drop or stabilize hole inclination. Meanwhile, when stop pump circulation, support head draws back so that stabilizer OD becomes small to improve tripping out smoothly.
