Downhole eccentric reamer tool and related systems and methods

A system for drilling a borehole in an earthen formation, the system comprising:

• a drillstring having a central axis, an uphole end, and a downhole end;
• a drill bit disposed at the downhole end of the drillstring coaxially aligned with the drillstring, wherein the drill bit is configured to rotate about the central axis in a cutting direction to drill the borehole;
• and
• a reaming tool coupled to the drillstring such that the reaming tool is positioned between the drill bit and the uphole end of the drillstring along the central axis, wherein the reaming tool comprises:
• a tubular body;
• and
• a plurality of blades circumferentially spaced along the tubular body, wherein each of the plurality of blades comprises:
• an uphole section that extends in a first helical direction about the central axis along the tubular body;
• a downhole section that extends in a second helical direction about the central axis along the tubular body, wherein the second helical direction is opposite the first helical direction;
• and
• an arcuate central section that continuously extends from the uphole section to the downhole section along the tubular body,
• wherein the plurality of blades are eccentric about the central axis such that the reaming tool is configured to pass axially through a first diameter and is configured to ream a borehole to a second diameter that is greater than the first diameter when the reaming tool is rotated about the central axis in a cutting direction,
• wherein the plurality of blades of the reaming tool comprises:
• one or more first blades on a first radial side of the reaming tool;
• and
• one or more second blades on a second radial side of the reaming tool that is radially opposite from the first radial side,
• wherein an outer surface of each of the first blades tapers toward the tubular body at an uphole end and a downhole end at a first rate,
• wherein an outer surface of each of the second blades tapers toward the tubular body at an uphole end and a downhole end at a second rate, and
• wherein the first rate is greater than the second rate.

A method for drilling a borehole, the method comprising:

• (a) coupling a drill bit to a lower end of a drillstring;
• (b) coupling a reaming tool to the drillstring between the drill bit and an uphole end of the drillstring, wherein the reaming tool comprises:
• a tubular body having a central axis;
• and
• a plurality of blades circumferentially spaced along the tubular body, wherein each of the plurality of blades comprises:
• an uphole section that extends in a first helical direction about the central axis along the tubular body;
• a downhole section that extends in a second helical direction about the central axis along the tubular body, wherein the second helical direction is opposite the first helical direction;
• and
• an arcuate central section that continuously extends from the uphole section to the downhole section along the tubular body,
• wherein the plurality of blades define a first outer diameter for the reaming tool;
• wherein the plurality of blades comprises:
• one or more first blades that have a first axial length extending from an uphole end to a downhole end of the one or more first blades, and wherein an outer surface of each of the one or more first blades tapers toward the tubular body at the uphole end and the downhole end of the one or more first blades at a first rate;
• and
• one or more second blades that have a second axial length extending from an uphole end to a downhole end of the one or more second blades, wherein an outer surface of each of the one or more second blades tapers toward the tubular body at the uphole end and the downhole end of the one or more second blades at a second rate,
• wherein the first axial length is different from the second axial length and the first rate is greater than the second rate;
• (c) lowering the reaming tool through a casing having an inner diameter that is greater than or equal to the first outer diameter of the reaming tool;
• (d) rotating the drill bit and the remaining tool in a cutting direction about the central axis after (c);
• and
• (e) reaming the borehole with the plurality of blades of the reaming tool during (c) to a reaming diameter that is greater than the first outer diameter of the reaming tool and the inner diameter of the casing.