Drilling in deviated and horizontal sections of a borehole can cause various problems with slime/sediment accumulation, resistance, and wear. When drilling in greatly inclined sections (e.g., over 65 degrees), for example, drilling mud moves along the top of the borehole above the drillpipe, but the mud fails to transport the slime and sedimentation accumulated on the borehole's lower wall. This type of accumulation also develops when drilling in horizontal sections, especially when the drilling tool operates in a “sliding” mode while correcting the well trajectory.
In addition, the tool joints between pipe sections on the drill string experience resistance against the slime/sediment accumulation when the drill string is moved in the borehole. “Cake” can quickly form at the tool joints as slime/sediment fills in at the joints. This quick caking process may cause hydraulic impact that affects the stability of the borehole walls. Although some of the caked slime/sediment may be dislodged by the mechanical rotation and movement of the drillpipe, full slime removal does not occur. Furthermore, the drillpipe's tool joints can significantly contact the borehole walls in a deviated or horizontal section, causing the joints to experience wear when the drillpipe rotates or moves.
There are steel drillpipes in the prior art that have grooves to reduce the drillpipe's contact with the borehole's wall. Examples of such steel drillpipes are disclosed in A. I. Bulatov, S. V. Dolgov, “Driller's Guide,” Moscow, Nedra, 2006, v. 1, p. 153, FIG. 8.8 and in U.S. Pat. No. 4,460,202. Steel drill collars in the prior art may also have grooves, such as disclosed in U.S. Pat. No. 6,012,744. These steel drillpipes and collars, however, can have limited use for drilling highly deviated or horizontal sections of a borehole because the pipe's weight creates high pressing loads that cause higher friction forces while the drillpipe/collar is moving and rotating in the borehole. In addition, the grooves are formed by milling on the outer surface of the steel and are shallow. Grooves machined in this manner do not effectively detach slime/sediment settled on the lower borehole wall.
A spiral-ribbed drillpipe 10 shown in
To couple the drillpipe 10 to other pipe or conduit, such as another drillpipe 10, a conventional steel drillpipe, a drill collar, etc., tool joints 40A-40B couple to the body's ends 22A-22B. In particular, tool joint 40A having thread 42A threads onto upper pin joint 23A, while tool joint 40B having thread 42B threads onto lower pin joint 23B. With tool joint 40A on end 22A, the cylindrical surface under the tool joint 40A provides an area to accommodate a casing spider and elevator for handling the drillpipe 10.
To deal with slime/sediment accumulation in a borehole, the pipe's intermediate portion 30 defines a plurality of ribs 32 extending along a length of the intermediate portion 30, although only one such rib 32 may be used in some implementations. Preferably, the ribs 32 have a right-handed twist and spiral along the intermediate portion 30, but a left-handed twist can also be used in some implementations. Likewise, the ribs 32 need not be spiraling and may in some implementations extend straight along the length of the intermediate portion.
Details of the ribs 32 are best shown in the cross-section of
Preferably, however, one or more of the active faces 34 can be cut inward from perpendicular so that the active face 34 defines an angle relative to the pipe body's outer surface and effectively scoops and transports any slime/sediment in the borehole. In other words, the active face 34 can define an incut angle θ that does not intersect the pipe's central axis C. This incut angle θ may be about 0 to 20-degrees, although deviations from this angle could be used depending on the desired implementation. In addition, the active faces 34 preferably have wear-resistant coatings 35, which can be a fine-grained, high-strength coating of chrome alloy, for example. The outside surfaces of the spiral ribs 32 adjoining the active faces 34 can also be partially covered with the same wear-resistant coating. As will be discussed in more detail below, these ribs 32 with their active faces 34 and recessed areas 36 help to relieve slime/sediment accumulation that may occur in a deviated or horizontal section of a borehole.
To prevent the intermediate portion 30 from significantly engaging sidewalls in a deviated or horizontal section, first and second bearings 50A-50B rotatably position on the cylindrical surfaces adjacent the ends 22A-22B of the drillpipe 10. For wear resistance, these bearings 50A-50B are preferably composed of a steel material and hardened. Moreover, the bearings 50A-50B preferably have wear-resistant coating bands 52, which can be composed of Relit hard alloy, for example.
As shown in
Use of the drillpipe 10 in a deviated or horizontal section of a borehole BH is illustrated in
When the drillstring is deployed downhole and drills through a formation FM, operators inject drilling mud through the drillstring to the bottomhole. This injected drilling mud passes through the pipe's internal bore 21 and activates the downhole motor, cools the drilling bit, and removes drilling cuttings through annulus to the surface. The spiraling ribs 32 and their corresponding active faces 34 and recessed areas 36 reduce the probability that the drillpipe 10 will stick in the borehole under differential pressure (difference between reservoir pressure and hydrostatic pressure in the hole). Moreover, the bearings 50A-50B help stabilize the bottomhole assembly because the drillpipe 10's overall outside diameter has a reduced clearance with the borehole wall.
As expected, however, drilling in the deviated section with high inclination (over 65 degrees) causes drilling cuttings and slime/sedimentation S to accumulate along the lower wall of the borehole BH. The accumulation may especially occur during a “sliding mode” of operation when the drill string is not rotating and is being moved to correct the well trajectory. In any event, the accumulation inhibits the drillstring's movement and rotation and may eventually lead to the drillstring sticking in the borehole BH.
The drillpipe 10 alleviates the problems caused by slime/sediment S by helping to clear the accumulation from the borehole BH and reduce the resistance experienced during operation. When the drillpipe 10 is rotating, for example, the intermediate portion 30's right-hand spiraling ribs 32 repeatedly interact with the slime/sediment accumulated on the borehole BH's lower wall. In this repeated interaction, the active faces 34 on the rib's leading edges scoop up the slime/sediment and transports it to the borehole BH's upper side where the typical upflow F of drilling mud can then carry the slime/sediment S uphole. With the right-hand spiraling, any engaged slime/sediment material can also be moved axially along the length of the drillpipe 10. This clearing of accumulated slime and sediment may allow operators to reduce the mud flow required during drilling, which in itself can produce a better value for the equivalent circulation density (ECD).
While the drillpipe 10 rotates, the bearings 50A-50B on the pipe 10 contact the borehole BH's walls. Being rotatable on the drillpipe 10, the bearings 50A-50B experience less revolutions than experienced by the pipe body 20. Accordingly, the bearing 50A-50B's reduced revolutions along with their anti-wear coatings 52 prolong their service life and reduce the torque required to rotate the drillpipe 10. Because the bearing's diameter DB (See
As noted previously, the drillpipe 10 is preferably composed of a lightweight alloy, such as aluminum alloy. Examples of suitable aluminum alloys include D16T (Russian standard GOST 4748) of the Al—Cu—Mg system or 1953 T1 of the Al—Zn—Mg system, although other suitable aluminum alloys for the wellbore environment may also be used. Compared with conventional steel pipes, the drillpipe 10 made from the lightweight alloy can reduce friction and resistance forces while moving and rotating the drillstring. In addition, the aluminum drillpipe 10 can be manufactured by extrusion so that different configurations and profiles for the spiraling ribs 32, active faces 34, and recessed areas 36 can be produced without the need for much machining, if any.
Being composed of aluminum alloy or the like, the drillpipe 10 preferably meets the ISO 15546 requirements for physical and mechanical properties after heat treatment and ageing. To further meet ISO 15546, the tool joints 40A-40B used to interconnect the drillpipe 10 are preferably composed of steel. In addition, the connections between tool joints 40A-40B and the drillpipe's ends 22A-22B preferably have tapered threads with a thread cross-section that is trapezoidal, and the connections preferably use tapered shoulders and internal stops to relieve some of the thread loads.
For some exemplary dimensions, the overall length of the drillpipe 10 can be about 9000-mm to about 12200-mm, with the drillpipe's ribbed intermediate portion 30 being about 105 to 200-mm. Diameters and wall thicknesses of the drillpipe 10 depend in part on the length of the drillpipe 10, the desired internal bore diameter, desired pipe size, etc. In general and with reference to
The foregoing description of preferred and other embodiments is not intended to limit or restrict the scope or applicability of the inventive concepts conceived of by the Applicants. In exchange for disclosing the inventive concepts contained herein, the Applicants desire all patent rights afforded by the appended claims. Therefore, it is intended that the appended claims include all modifications and alterations to the full extent that they come within the scope of the following claims or the equivalents thereof.
This is a non-provisional of U.S. Provisional Application Ser. No. 61/025,451, filed Feb. 1, 2008, which is incorporated herein by reference and to which priority is claimed.
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Number | Date | Country | |
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Number | Date | Country | |
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61025451 | Feb 2008 | US |