Abstract
The excessive drag/torque and the backing pressure is an important factor that restricts the improvement of the penetration rate and the extension of the drilling in the sliding drilling process of extended-reach wells and horizontal wells. To deal with this problem, this paper developed a novel controllable hybrid steering drilling system (CHSDS) based on the friction-reducing principle of a rotating drill string. The CHSDS is composed of a gear clutch, hydraulic system, and measurement and control system. By controlling the meshing and separation of the clutch with the mud pulse signal, the CHSDS has two working states, which leads to two boundary conditions. Combined with the stiff-string drag torque model, the effects of the drilling parameters on the friction-reducing performance of the CHSDS are analyzed systematically. The results show that the friction reduction effect in the inclined section is the most significant, followed by that in the horizontal section, whereas there is almost no impact in the vertical section. Friction reduction increases with the rotary speed and the drilling fluid density, whereas it decreases with the increase in the surface weight-on-bit and the bit reaction torque. Field tests confirm the separation and meshing function of the CHSDS. The developed controllable hybrid steering and friction-reducing technology provides an alternative approach for the safe and high-efficiency drilling of horizontal wells.
Highlights
Realizing economical and high-efficiency exploitation of unconventional oil and gas resources depends on combining horizontal drilling and hydraulic fracturing technologies [1]
In the analysis of the drill string friction based on Coulomb’s theorem, the solution of the normal contact force is the key. e contact state between the drill string and the borehole wall is uncertain because of factors; it is very difficult to accurately solve the normal contact force. us, it is necessary to make appropriate assumptions about the contact and deformation of the drill string [26,27,28]: (1) e drill string is in continuous contact with the borehole wall, the borehole wall is rigid, and the deformation of the drill string is within the elastic range
When the controllable hybrid steering drilling system (CHSDS) is in the meshing state, like conventional rotary drilling, the drill string rotates as a whole, and the wellhead torque and the bit reverse torque are known. e wellhead torque is the external torque exerted by the rotary table or the top drive, and the bit torque is the reverse torque produced by the positive displacement motor (PDM). erefore, the boundary conditions are as follows [33]: Measurement and control system
Summary
Realizing economical and high-efficiency exploitation of unconventional oil and gas resources depends on combining horizontal drilling and hydraulic fracturing technologies [1]. Us, various advanced drag-reduction tools are developed and successful field applications are achieved, such as drill pipe bearing subs, hydraulic oscillators, rotary steering systems (RSSs), and drill string rocking systems [7,8,9,10]. Based on the principle of friction reduction by a rotary drill string, a novel controllable hybrid steering drilling system (CHSDS) is developed, which can switch freely between meshing and separation states by receiving remotely controlled commands from the ground. Because there are two working states of meshing and separation in the actual drilling of the CHSDS, the boundary conditions of the traditional drag torque model are no longer applicable. Erefore, based on the actual working conditions of the CHSDS, the boundary conditions of its separation or meshing states and of the bit are determined. e dragreduction performance of the CHSDS is analyzed by combining with the classical drag torque model of the drill string. e field test verifies the remote separation and meshing functions of the CHSDS, providing the basis for the drag-reduction performance test and the subsequent application of the CHSDS
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