Motor Driven Hybrid Rotary Steerable System

Abstract

Abstract of Disclosure A bottom hole assembly is rotatably adapted for drilling directional boreholes into an earthen formation. It has an upper stabilizer mounted to a collar, and a rotary steerable system. The rotary steerable system has integral drilling motor, an upper section connected to the collar, a steering section, and a drill bit arranged for drilling the borehole attached to the steering section. The steering section is joined at a swivel with the upper section. The steering section is actively tilted about the swivel. A lower stabilizer is mounted upon one of the upper section or the steering section such that the swivel is intermediate the drill bit and the lower stabilizer.

Description

Background of Invention[0001] 1. Field of the Invention.[0002] This invention relates to a bottom hole assembly comprising a rotary steerable directional drilling tool with an integral drilling-motor, which is useful when drilling boreholes into the earth.[0003] 2. Description of the Related Art.[0004] Rotary steerable drilling systems for drilling deviated boreholes into the earth may be generally classified as either "point-the-bit"systems or "push-the-bit"systems. In the point-the-bit system, the axis of rotation of the drill bit is deviated from the local axis of the bottom hole assembly (BHA) in the general direction of the new hole. The hole is propagated in accordance with the customary three point geometry defined by upper and lower stabilizer touch points and the drill bit. The angle of deviation of the drill bit axis coupled with a finite distance between the drill bit and lower stabilizer results in the non-collinear condition required for a curve to be generated. There a...

AI Technical Summary

Benefits of technology

[0011] In this arrangement, the location of the contact between the drill bit and the formation is defined by the offset angle of the axis of the drill bit from the tool axis and the distance between the drill bit and the swivel. The theoretical build rate of the tool is then defined by the radius of curvature of a circle determined by this contact point and the two contact points between the formation and the upper stabilizer and lower stabilizer. The dogleg is also influenced by the side cutting characteristic of the bitA drilling fluid actuated motor system is used to point the portion of the steering section rigidly attached to the drill bit. Such a system utilizes the "free" hydraulic energy available in the drilling fluid as it is pumped through the tool to displace motors and / or pads to control the orientation of the tool while drilling. This minimizes the amount of electrical power that must be developed downhole for toolface control. Further, control of a motor system may be accomplished by numerous mechanical and electrical means, for example rotary disc valves to port drilling fluid to the requite actuators or similar arrangements utilizing solenoid actuated valves, affording great flexibility in implementation.

Problems solved by technology

Changes in hole gauge and stabilizer wear effectively cause the bit to be pointed in a particular direction, which may or may not help the steering response, regardless of steering system type.

In the extreme, push-the-bit systems that use drill bits with little or no side cutting ability may still achieve limited steering response by virtue of the aforementioned flexibility of the BHA or stabilizer / hole gauge effects.

An additional problem occurs when extremely small bend radiuses are included in the build.

Mechanical fatigue in the drill pipe may occur as it is rotated in bending.

When the bend is sharp and the drilling rate is slow, the fatigue life of the drill pipe may be exceeded, leading to either "tripping" the pipe to replace it, or failure of the pipe.

Unfortunately, adding a drilling-motor to the BHA can cause the assembly to be too long to easily pass through the bend section to begin drilling.

Adding a motor makes the assembly longer - and what ever is beneath the motor is subject to high cyclic bending forces when going through a tight bend.

There are numerous other problems as well particularly when the minimum speed of the drilling-motor approaches the maximum speed of the rotary steerable tool.

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