Patent Application
20090260894
This invention relates to drill bits, specifically drill bit assemblies for use in oil, gas and geothermal drilling. Often drill bits are subjected to harsh conditions when drilling below the earth's surface. Replacing damaged drill bits in the field is often costly and time consuming since the entire downhole tool string must typically be removed from the borehole before the drill bit can be reached. Bit whirl in hard formations may result in damage to the drill bit and reduce penetration rates. Further, loading too much weight on the drill bit when drilling through a hard formation may exceed the bit's capabilities and also result in damage. Too often unexpected hard formations are encountered suddenly and damage to the drill bit occurs before the weight on the drill bit may be adjusted.
The prior art has addressed bit whirl and weight on bit issues. Such issues have been addressed in the U.S. Pat. No. 6,443,249 to Beuershausen, which is herein incorporated by reference for all that it contains. The '249 patent discloses a PDC-equipped rotary drag bit especially suitable for directional drilling. Cutter chamfer size and backrake angle, as well as cutter backrake, may be varied along the bit profile between the center of the bit and the gage to provide a less aggressive center and more aggressive outer region on the bit face, to enhance stability while maintaining side cutting capability, as well as providing a high rate of penetration under relatively high weight on bit.
U.S. Pat. No. 6,298,930 to Sinor which is herein incorporated by reference for all that it contains, discloses a rotary drag bit including exterior features to control the depth of cut by cutters mounted thereon, so as to control the volume of formation material cut per bit rotation as well as the torque experienced by the bit and an associated bottomhole assembly. The exterior features preferably precede, taken in the direction of bit rotation, cutters with which they are associated, and provide sufficient bearing area so as to support the bit against the bottom of the borehole under weight on bit without exceeding the compressive strength of the formation rock.
U.S. Pat. No. 6,363,780 to Rey-Fabret which is herein incorporated by reference for all that it contains, discloses a system and method for generating an alarm relative to effective longitudinal behavior of a drill bit fastened to the end of a tool string driven in rotation in a well by a driving device situated at the surface, using a physical model of the drilling process based on general mechanics equations. The following steps are carried out: the model is reduced so to retain only pertinent modes, at least two values Rf and Rwob are calculated, Rf being a function of the principal oscillation frequency of weight on hook WOH divided by the average instantaneous rotating speed at the surface, Rwob being a function of the standard deviation of the signal of the weight on bit WOB estimated by the reduced longitudinal model from measurement of the signal of the weight on hook WOH, divided by the average weight on bit defined from the weight of the string and the average weight on hook. Any danger from the longitudinal behavior of the drill bit is determined from the values of Rf and Rwob.
U.S. Pat. No. 5,806,611 to Van Den Steen which is herein incorporated by reference for all that it contains, discloses a device for controlling weight on bit of a drilling assembly for drilling a borehole in an earth formation. The device includes a fluid passage for the drilling fluid flowing through the drilling assembly, and control means for controlling the flow resistance of drilling fluid in the passage in a manner that the flow resistance increases when the fluid pressure in the passage decreases and that the flow resistance decreases when the fluid pressure in the passage increases.
U.S. Pat. No. 5,864,058 to Chen which is herein incorporated by reference for all that is contains, discloses a downhole sensor sub in the lower end of a drillstring, such sub having three orthogonally positioned accelerometers for measuring vibration of a drilling component. The lateral acceleration is measured along either the X or Y axis and then analyzed in the frequency domain as to peak frequency and magnitude at such peak frequency. Backward whirling of the drilling component is indicated when the magnitude at the peak frequency exceeds a predetermined value. A low whirling frequency accompanied by a high acceleration magnitude based on empirically established values is associated with destructive vibration of the drilling component. One or more drilling parameters (weight on bit, rotary speed, etc.) is then altered to reduce or eliminate such destructive vibration.
In one aspect of the present invention, a drill bit has an axis of rotation and a working face with a plurality of blades extending outwardly from a bit body. The blades form in part an inverted conical region and a plurality of cutters with a cutting surface is arrayed along the blades. A jack element is coaxial with the axis of rotation and extended within the conical region within a range defined by the cutting surface of at least one cutter.
The cutters and a distal end of the jack element may have hard surfaces, preferably over 63 HRc. Materials suitable for either the cutter or the jack element may be selected from the group consisting of diamond, polycrystalline diamond, natural diamond, synthetic diamond, vapor deposited diamond, silicon bonded diamond, cobalt bonded diamond, thermally stable diamond, polycrystalline diamond with a binder concentration of 1 to 40 weight percent, infiltrated diamond, layered diamond, polished diamond, course diamond, fine diamond cubic boron nitride, chromium, titanium, aluminum, matrix, diamond impregnated matrix, diamond impregnated carbide, a cemented metal carbide, tungsten carbide, niobium, or combinations thereof.
The jack element may have a distal end with a blunt geometry with a generally hemi-spherical shape, a generally flat shape, a generally conical shape, a generally round shape, a generally asymmetric shape, or combinations thereof. The blunt geometry may have a surface area greater than the surface area of the cutting surface. In some embodiments, the blunt geometry's surface is twice as great as the cutting surface.
Depending on the intended application of the bit, various embodiments of the bit may out perform in certain situations. The bit may comprise three to seven blades. Cutters attached to the blades may be disposed at a negative back rake angle of 1 to 40 degrees. Some of the cutters may be positioned at different angles. For example the cutters closer to the jack element may comprises a greater back rake, or vice versa. The diameter of the cutters may range for 5 to 50 mm. Cutters in the conical region may have larger diameters than the cutters attached to the gauge of the bit or vice versa. Cutting surfaces may comprise a generally flat shape, a generally beveled shape, a generally rounded shape, a generally scooped shape, a generally chisel shape or combinations thereof. Depending on the abrasiveness of the formation back-up cutters may also be desired. The bit may comprise various cone and flange angles as well. Cone angles may range from 25 to 155 degrees and flank angles may range from 5 to 85 degrees. The gauge of the bit may be 0.25 to 15 inches. The gauge may also accommodate 3 to 21 cutters.
The jack element may extends to anywhere within the conical region, although preferably 0.100 to 3 inches. The jack element may be attached within a pocket formed in the working face of the bit. It may be attached to the bit with a braze, a compression fit, a threadform, a bond, a weld, or a combination thereof. In some embodiments, the jack element is formed in the working face. In other embodiments, the jack element may be tapered. In other embodiments, a channel may connect the pocket to the bore. Such a channel may allow air or enter or exit the pocket when the jack element is inserted or removed and prevent a suction effect. A portion of the working face may extend adjacent the jack element in such a manner as to support the jack element against radial loads. In some embodiments, the working face has cross sectional thickness of 4 to 12 times the cross sectional thickness of the jack element. The working face may also have 4 to 12 times the cross sectional area as the jack element.
A jack element 104 is substantially coaxial with an axis 105 of rotation and extends within the conical region 103. The jack element 104 comprises a distal end 206 which falls within a range 320 (see
The jack element 104 may be disposed within a pocket 301 formed in the bit body 201. The jack element 104 is brazed, press fit, welded, threaded, nailed, or otherwise fastened within the pocket 301. In some embodiments, the tolerances are tight enough that a channel 302 is desirable to allow air to escape upon insertion into the pocket 301 and allow air to fill in the pocket 301 upon removal of the jack element 104. A plug 303 may be used to isolate the internal pressure of the drill bit 100 from the pocket 301. In some embodiments, there is no pocket 301 and the jack element 104 is attached to a flat portion of the working face.
The drill bit 100 may be made in two portions. The first portion 305 may comprise at least the shank 200 and a part of the bit body 201. The second portion 310 may comprise the working face 202 and at least another part of the bit body 201. The two portions 305, 310 may be welded together or otherwise joined together at a joint 315.
The diameter of the jack element 104 may affect its ability to lift the drill bit 100 in hard formations. Preferably, the working face 202 comprises a cross sectional thickness 325 of 4 to 12 times a cross sectional thickness 320 of the jack element 104. Preferably, the working face 202 comprises a cross sectional area of 4 to 12 times the cross sectional area of the jack element 104.
One long standing problem in the industry is that cutters 102, such as diamond cutters, chip or wear in hard formations when the drill bit 100 is used too aggressively. To minimize cutter 102 damage, the drillers will reduce the rotational speed of the bit 100, but all too often, a hard formation is encountered before it is detected and before the driller has time to react. With the present invention, the jack element 104 may limit the depth of cut that the drill bit 100 may achieve per rotation in hard formations because the jack element 104 actually jacks the drill bit 100 thereby slowing its penetration in the unforeseen hard formations. If the formation 400 is soft, the formation may not be able to resist the WOB loaded to the jack element 104 and a minimal amount of jacking may take place. But in hard formations, the formation may be able to resist the jack element 104, thereby lifting the drill bit 100 as the cutters 102 remove a volume of the formation during each rotation. As the drill bit 100 rotates and more volume is removed by the cutters 102 and drilling mud, less WOB will be loaded to the cutters 102 and more WOB will be loaded to the jack element 104. Depending on the hardness of the formation 400, enough WOB will be focused immediately in front of the jack element 104 such that the hard formation will compressively fail, weakening the hardness of the formation and allowing the cutters 102 to remove an increased volume with a minimal amount of damage.
Typically, WOB is precisely controlled at the surface of the well bore to prevent over loading the drill bit 100. In experimental testing at the D.J. Basin in Colorado, crews have added about 5,000 more pounds of WOB than typical. The crews use a downhole mud motor in addition to a top-hole motor to turn the drill string. Since more WOB increases the depth-of-cut the WOB added will also increase the traction at the bit 100 which will increase the torque required to turn the bit 100. Too much torque can be harmful to the motors rotating the drill string. Surprisingly, the crews in Colorado discovered that the additional 5,000 pounds of WOB didn't significantly add much torque to their motors. This finding is consistent with the findings of a test conducted at the Catoosa Facility in Rogers County, Oklahoma, where the addition of 10,000 to 15,000 pounds of WOB didn't add the expected torque to their motors either. The minimal increase of torque on the motors is believed to be effected by the jack element 104. It is believed that as the WOB increases the jack element 104 jacks the bit 100 and then compressively fails the formation 400 in front of it by focusing the WOB to the small region in front of it and thereby weakens the rest of the formation 400 in the proximity of the working face 202. By jacking the bit 100, the depth of cut in limited, until the compressive failure of the formation 400 takes place, in which the formation 400 is weaker or softer and less torque is required to drill. It is believed that the shearing failure and the compressive failure of the formation 400 happen simultaneously.
As the cutters 102 along the inverted conical region 103 of the drill bit 100 remove portions of the formation 400 a conical profile 401 in the formation 400 may be formed. As the jack element 104 compressively fails the conical profile 401, the formation 400 may be pushed towards the cutters 102 of the conical portion 103 of the blades 101. Since cutting at the axis of rotation 105 is typically the least effective (where the cutter 102 velocity per rotation is the lowest) the present invention provides an effective structure and method for increasing the rate of penetration (ROP) at the axis of rotation. It is believed that it is easier to compressively fail and displace the conical profile 401 closer to its tip than at its base, since there is a smaller cross sectional area. If the jack element 104 extends too far, the cross sectional area of the conical profile 401 becomes larger, which may cause it to become too hard to effectively compressively fail and/or displace it. If the jack 104 extends beyond the leading most point 410 of the leading most cutter 402, the cross sectional area may become indefinitely large and extremely hard to displace. In some embodiments, the jack element 104 extends within 0.100 to 3 inches. In some embodiments, the jack element 104 extends within the cutting surface of cutter 403.
As drilling advances, the jack element 104 is believed to stabilize the drill bit 100 as well. A long standing problem in the art is bit whirl, which is solved by the jack element 104 provided that the jack 104 extends beyond the cutting surface 210 of at least one of the cutters 1400 within the conical region 103. The leading most cutter 402 may be attached to the nose 204 of at least one of the blades, preferably the jack element 104 does not extend beyond the cutting surface of cutter 402. The trailing most cutter 403 within the conical region 103 may be the cutter 403 closest to the axis 105 of rotation. Preferably the distal end 106 of the jack element 104 extends beyond the trailing most point 415 of cutter 403. Surprisingly, if the jack element 104 does not extend beyond the trailing most point 415 of the trailing most cutter 403, it was found that the drill bit 100 was only as stable as the typical commercially available shear bits. During testing it was found in some situations that if the jack element 104 extended too far, it would be too weak to withstand radial forces produced from drilling or the jack element 104 would reduce the depth-of-cut per rotation greater than desired. In some embodiments, the jack element 104 extends within a region defined as the depth of cut 405 of at least one cutter, which may be the trailing most cutter 403.
One indication that stability is achieved by the jack element 104 is the reduction of wear on the gauge cutters 1401. In the test conducted at the Catoosa Facility in Rogers County, Oklahoma the present invention was used to drill a well of 780 ft in 6.24 hours through several formations including mostly sandstone and limestone. During this test it was found that there was little to no wear on any of the polycrystalline diamond cutters 1401 fixed to the gauge of the drill bit 100—which was not expected, especially since the gauge cutters 1401 were not leached and the gauge cutters 1401 had an aggressive diameter size of 13 mm, while the cutters 1400 in the conical region 103 had 19 mm cutters. It is believed that this reduced wear indicates that there was significantly reduced bit whirl and that the drill bit 100 of the present invention drilled a substantially straight hole. The tests conducted in Colorado also found that the gauge cutters 1401 no little or no wear.
Also shown in
Whereas the present invention has been described in particular relation to the drawings attached hereto, it should be understood that other and further modifications apart from those shown or suggested herein, may be made within the scope and spirit of the present invention.
This patent application is a continuation of U.S. patent application Ser. No. 11/535,036, which is a continuation-in-part of U.S. patent application Ser. No. 11/278,935, which is a continuation-in-part of U.S. patent application Ser. No. 11/277,394, which is a continuation-in-part of U.S. patent application Ser. No. 11/277,380, which is a continuation-in-part of U.S. patent application Ser. No. 11/306,976, which is a continuation-in-part of U.S. patent application Ser. No. 11/306,307, which is a continuation-in-part of U.S. patent application Ser. No. 11/306,022, which is a continuation-in-part of U.S. patent application Ser. No. 11/164,391. All of these applications are herein incorporated by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11535036 | Sep 2006 | US |
| Child | 12475344 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11278935 | Apr 2006 | US |
| Child | 11535036 | US | |
| Parent | 11277394 | Mar 2006 | US |
| Child | 11278935 | US | |
| Parent | 11277380 | Mar 2006 | US |
| Child | 11277394 | US | |
| Parent | 11306976 | Jan 2006 | US |
| Child | 11277380 | US | |
| Parent | 11306307 | Dec 2005 | US |
| Child | 11306976 | US | |
| Parent | 11306022 | Dec 2005 | US |
| Child | 11306307 | US | |
| Parent | 11164391 | Nov 2005 | US |
| Child | 11306022 | US |
