Patent Application
20130180781
The field of the invention is reaming bits and more particularly those used on high speed, low torque turbines or motors attached to the leading end of a casing or liner string. The bits having profile characteristics that reduce torque fluctuations due to unpredictable variations in weight on bit.
When running a casing or liner into a predrilled bore hole, it is desirable that the bore hole will have been drilled with the intended shape, to its designed diameter, and without marked deviations, such as doglegs, along its path. Unfortunately, due to unstable, heterogeneous formations, irregularities such as stringers within a formation, poor drilling practices, damage and wear of drill bits and bottom hole assemblies (BHA) and various other factors, the ideal bore hole is rarely achieved.
Therefore, it is desirable to provide the casing or liner string being run into the existing bore hole with a cutting structure at the leading end thereof to enable enlargement, as necessary, of portions of the bore hole so that the casing or liner may be run smoothly into the bore hole to the full extent intended. Initially the entire liner or casing string was rotated while it was being lowered into the borehole, which required powerful and complex drive systems at the surface. More recent projects use a hollow turbine or motor at the leading end of the casing string which are driven by drilling fluid pumped from the surface. It provides for a more efficient and economical transfer of power from the surface to the drill bit but it also limits the amount of torque that can be delivered to the bit and most of the power is in the form of high rotational speed. This most recent approach of using high speed turbines to provide a casing or liner string with a reaming capability has yielded inconsistent results with conventional, bullet shaped reaming bits.
In U.S. Pat. No. 7,621,351 a reamer bit having a substantially tubular body and a nose portion with a concave center extends from the nose portion to the side wall through a tapered shoulder region. The reaming tool further comprises a cutting structure for enlarging, also termed “reaming,” of a bore hole through contact with the side wall thereof. The term “tool” is used herein in a non-limiting sense, and embodiments of the present invention may also be characterized as a reaming bit or reaming shoe. In some embodiments, the nose portion of the reaming tool has at least one port therethrough extending to the interior of the body. In some embodiments, a plurality of circumferentially spaced, spirally configured blades extend on the exterior of the body from proximate the shoulder transition region to the gage and define junk slots there between. An axially leading end of each blade commences with substantially no standoff from the body and tapers radially outwardly to a portion having a substantially constant standoff and having a radially inwardly extending, beveled, axially trailing end. A plurality of cutting elements are disposed along a rotationally leading edge of each blade. The nose of this tool can be drilled out in a related method to allow further completion of the well.
In the past reaming tools that were surface driven turned typically in an RPM range of about 40-80 RPM and the large diameter, stiff casing was able to transmit high levels of torque. Turbines or high speed motors driven at speeds of 300-600 RPM and higher can only supply a fraction of the torque provided by top drives or rotary tables. Due to the lower torque capacity of the turbines the reaming tools that were previously serviceable experienced a great deal of stalling, reduced rates of penetration and generally unreliable performance. Typically these reamers had a bullet shaped profile 10, shown in
While the various reamers described above functioned fairly well at higher torque and slower RPM, the recent advent of a turbine driving a reamer with less torque at significantly higher speeds of 300-600 RPM and above produced an unacceptable level of torque fluctuation and stalling of the turbines. The present invention was developed to address this situation and enhance the performance of reamers in turbine applications by making modifications to the profile and other design features as will be described below. One of the approaches was the profile modification and shortening of the PL by using a plurality of arcuate surfaces between the gauge dimension 12 and bottom taper 28 and eliminating the long, low angle, tapered segment 18 of
A reaming bit designed to operate with low torque fluctuation when driven with a turbine at speeds in the order of 300-600 RPM and above features a profile that is arcuate from the gage dimension to the nose area or alternatively has a greater than 30 degrees, straight taper section and a profile length (PL) to bit size (BS) ratio of under 0.75. The blade spacing is asymmetrical but the reamer itself is mass balanced. The blades extend into a concave cone section towards the center and the cutting structure and nozzle arrangement cover the entire profile to ensure continued drilling if the reamer encounters an obstructed bore hole and/or has to disperse a built-up of cuttings. The blades start with long, smooth and partially spiraled gage pads on the periphery of the reamer and transition into the blade cutting structure with increased exposure, primary cutting elements on the leading edge. An array of protrusions are disposed behind the primary cutting elements to limit depth of cut to further enhance high speed stability and to protect the outer casing on run in.
In the preferred embodiment the profile between the gage section and the nose is fully arcuate but an alternative can be a reconfiguration of the existing profile for a reamer tool shown in
Referring to
Referring to
At the lower end there is a diametrical step up 104 of about 0.050 to 0.110 inches to transition to the blades 80 which have cutting elements on their leading side. The gage pads 98 are radially slightly smaller than the adjacent, actively cutting blades to assure smooth, passive contact with the borehole wall during rotation. They are partially spiraled with a bend 106 at the transition to the straight portion. The spiraling provides more circumferential contact and with the smooth surface and slight recess adds lateral stability to the reamer tool at high rotational speeds. An array of wear resistant, hard metal inserts 108 are inserted into the gage pad surface to provide wear resistance and maintain the critical gage diameter over the life of the reamer.
At step up 104 the gage pads transition into the actively cutting blades with primary hard metal or PDC cutting elements 88 at the leading edge. For drilling at high speed it is desirable to limit and control the depth of cut (DOC) or advance per revolution of the reamer to dampen both axial and torsional vibrations in mixed and interbedded formations. To control the depth of cut, a series of protrusions 112 and 114 are located generally behind and rotationally in line with the primary cutting elements 88. The exposure of these protrusions is less than that of primary inserts 88 and is adjustable based on the particular application. The protrusions 112 and 114 also protect the already existing, outer casing that the reamer may need to traverse before reaching the open hole segment to be reamed,’ limit the side cutting aggressiveness and thus improve directional stability in inclined and horizontal wells. The protrusions can be hard metal or PDC inserts or appropriate shapes of hardfacing material welded to the outer surface of the blades. Another way to reduce the exposure of the primary cutting elements 88 is by depositing of a layer of hardfacing material across the entire outer blade surface or parts thereof.
Another important feature to reduce harmful torsional and lateral accelerations is the asymmetrical spacing of the blades to prevent the formation of a repetitive pattern on the borehole bottom and prevent the harmonics produced by evenly spaced blades. This is accomplished by having a standard deviation of at least 5 degrees in the angular spacing between blades.
The concave shape of the central part 86 of the reamer assures that it can be milled or drilled-out from the center to the shoulder without the risk of leaving any un-drilled parts downhole which could damage the next bit or bottom hole assembly.
One or more rupture discs 92 are provided with communication to the internal passages that lead to inner nozzles 94 and outer nozzles 96 so that in the event there is a nozzle obstruction and pressure builds up the rupture discs 92 will break and fluid circulation can continue uninterrupted. The inner nozzles are particularly important to assure adequate cleaning when the borehole is filled with excess cuttings from the reaming process itself or accumulation of cuttings in front of the reamer.
Those skilled in the art will appreciate that the reaming tool of the present invention designed to operate at speeds in the order of 300-600 RPM and higher has features that limit torque fluctuation using an arcuate profile between the gage section and concave cone section so as to eliminate an aggressive tapered section and shorten the profile length. An alternative design retains a straight tapered segment in the profile but the taper is greater than 30 degrees and the PL/BS ratio is smaller than 0.75 to shorten the height of the reaming tool and thus reduce torque fluctuation and stalling tendencies at high rotational speeds. The ability of the reamer to drill-out fully or partially obstructed holes is greatly enhanced by extending at least some of the blades with PDC cutting elements into the concave cone section and near to the center. Other features that aid the dynamic stability are asymmetrical spacing of the blades, depth of cut control through reduced exposure of the primary cutting elements and smooth spiraled and slightly recessed gage pads to restrict lateral motion. The row or rows of protrusions behind the primary PDC cutters promote not only dynamics stability but also reduce the side cutting aggressiveness when reaming an inclined wellbore and protect already existing outer casing when the next casing string with the turbine/reamer at its leading end is run into the borehole.
The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below:
