Methods for directing vertical drilling

摘要

Methods allowing precise directional drilling are provided. Such methods include use of directional drilling equipment which include a drill string with a hollow bottom rod connected to a boring tool by means of an obtuse-angle connection piece or “bent sub”. In order to restore the verticality of the drilling a vertical borehole section (F) is formed and then a probe equipped with an inclinometer is lowered inside the bottom rod. The string may be rotated into four angular positions and the inclination values of the probe in each angular position are detected at the depth reached. The string is rotated so as to bring it into an angular position corresponding to the maximum inclination value detected. The string is moved so as to move the boring tool further downwards and the inclination of the probe is detected again in order to check that verticality has been reached.

主权项

1. A method for directing vertical drilling performed by means of directional drilling equipment, the equipment comprising:
a drill string at the bottom end of which a hollow bottom rod defining a first longitudinal axis is mounted; a down-hole assembly including a boring tool defining a second longitudinal axis and a rigid connector bent at an obtuse angle or bent sub which rigidly connects the tool to the bottom rod such that the first and the second axes form a predetermined obtuse angle; wherein said method comprises the following steps for restoring verticality of the drilling: a) drilling a substantially vertical borehole section by means of said equipment; b) stopping the movement of the string upon reaching a predetermined drilling depth; c) lowering a probe equipped with an inclinometer into the hollow bottom rod; d) keeping the drill string at said reached drilling depth, performing the following steps d1)-d5): d1) detecting, by means of the inclinometer, the value (I0) of the inclination of the probe with respect to the vertical in a first angular position; d2) rotating the string around its longitudinal axis to a second angular position; d3) detecting, by means of the inclinometer, the value (I90) of the inclination of the probe with respect to the vertical in the second angular position; d4) repeating steps d2) and d3) so as to obtain further inclination values (I180, I270) of the probe in other angularly spaced positions around the axis of the string; d5) rotating the string so as to bring it into a selected angular position corresponding to the maximum inclination value detected, or into an intermediate angular position between the angular positions at which two maximum inclination values were detected; e) causing the boring tool to advance further down, bringing the tool to a sunken position, with the drill string approximately orientated in said selected angular position; f) interrupting the downward advancing motion of the tool and detecting again the inclination value given by the inclinometer; g) obtaining, by means of the drilling equipment, a subsequent substantially vertical borehole section; and h) repeating steps b) to g).