Bottom hole assembly for directional drilling

Abstract

The bottom hole assembly of the present invention includes a drill bit driven by a positive displacement drilling motor, the motor being constructed of tubular housings, one of said housings having a bend so as to cause the bit to drill directionally, another housing containing a rotor and stator to generate power, and a flexible section between the power generation housing and the bend. A stabilizer is disposed on one end of the flexible section for engaging the wall of the borehole and the housing with the bend includes a wear pad for engaging the lower side of the borehole. The bottom hole assembly contacts the borehole at three contact points, namely at the stabilizer, the wear pad, and the drill bit, for producing the necessary build-up rate, along with the bend, and thus the curvature of the borehole being drilled. The flexible section has a stiffness which is less than the stiffness of the housing of the stator and has a stiffness which is on the order of 33% or less of that of the power generation housing. The stiffness is determined by the selection of the material, wall thickness and length of the flexible section such that the desired flexibility is achieved, but the necessary torsional strength and axial load capabilities are maintained. The purpose of the flexible section is to allow the bottom hole assembly to be configured to achieve high build rates, on the order of 20 to 70 degrees per hundred feet, without generating excessively high loads and stresses on the bit and other bottom hole assembly components.

Dependencies are inferred from the claim text.