US 3382938 A
Description (OCR text may contain errors)
May 14, 1968 E. B. wlLLlAMs, JR
DR ILL COLLAR Filed Oct. 5, 1966 v INVE'NTOR. fdWa/'a/B. W//ams ./f.
United States Patent O 3,382,938 DRILL COLLAR Edward l. Williams, lr., Greenville, Tex., assignor of one-third each to Edward B. Williams III, Joseph W. Williams, and David B. Williams, all of Greenville, Tex.
Filed (let. 3, 1966, Ser. No. 583,698 10 Claims. (Cl. 175-325) This invention relates to drill collars used in rotary drilling of a borehole through earth formations to substantial depths, and particularly to an improved drill collar for controlling deviation of the drill bit from its intended course.
'Usually drill collars consist of one or more lstands of heavy-walled drill pipe that are inserted into the drilling string just above the drill bit in an attempt to maintain a stili stem for the bit. The drill collars, together with the drill pipe secured thereto, provide an elongated heavyweight column of metal that pushes the drill bit against the bottom of the borehole as the drill bit is rotated. Due to the length and yieldability of the string of drill pipe, the drill pipe bends under compression of its own weight, and makes contact with the wall of the borehole at various points along the length thereof. lt is obvious that as the weight increases toward the bottom of the borehole, the spacing between points of contact becomes less, and in spite of the increased rigidity afforded by the drill collars, there is suliicient bend therein to carry the drill bit toward the wall of the borehole. When the drilling operations are carried out with the drill collar in contact with the wall of the borehole by bending, the axis of rotation remains in the center of the collar as it rotates about its bent axis, thereby aiming the drill bit at an angle to the true axis of the borehole. Consequently, the bit continuously deliects from its intended drilling position, to produce a crooked hole. When the drill bit encounters a dipping formation, this deflection of the borehole is aggravated because the drill bit tries to drill in a direction normal to the plane of the formation.
Many schemes have been devised to correct angularity of the drill bit, such as inserting a relatively short offset coupling between the lower end of the lowermost drill collar and the bit to compensate for deflection of the bit by the drill collar and thereby hold the drill bit on its intended course, however, such couplings are not satisfactory.
Another method is to use a drill collar having a section modulus therein which produces a predominately greater bend in the drill collar at the point of contact with the Wall of the borehole and which locks under weight to hold the bit centered in the borehole. Such a drill collar is readily moved into and out of the borehole because the induced bend straightens out when the drill bit is lifted od the bottom of the hole. But the section modulus is provided by reducing the cross section of the drill at the point of the bend, so that the strength of the drill collar is sacrificed. Also, contact with the wall of the borehole is rather abrupt and there is insuflicient guiding of the stern.
A still further method is to use a drill collar wherein the major portion is offset on an axis parallel with the axis of the tool joints which couple the drill collars into the drilling string, the offset being in the manner of a crank and in an amount sufiicient to maintain bearing contact with the wall of the borehole, and the offset being of sufficient length to hold the drill bit in a straight course. The difficulty here is in producing the bends in a thickwalled drill pipe to attain the crank effect required for the offset. Also, the continuous contact of the olfset along the length thereof interferes with flow of the drilling iiuid and cuttings carried thereby.
3,382,938 Patented May 14a, 1968 lCC With the above in mind, it is the object of the present invention to provide drill collars of more rigid character and which carry a series of spaced apart pads extending radially from one side of the collar and having faces in wiping contact with the Wall of the borehole. The pads thus support the collar along substantially the full length thereof to maintain the drill bit in the desired drilling axis and prevent deviation because of bending of the drill collar or tendency of the drill bit to follow dipping formations.
It is also an object of the invention to provide the drill collar with a permanent curvature or Warp on the side thereof having the pads, to assure that if curvature of the drill collar should occur under weight of the column of drill pipe, the curvature develops on the side having the pads, thereby retaining the pads in wiping contact with the wall of the borehole.
Other objects of the invention are to provide a drill collar `which more efficiently accomplishes its intended purpose, and to provide a drill collar which is easily produced without weakening the strength of the collar.
ln accomplishing these and other objects of the invention as hereinafter pointed out, improved structure is provided as illustrated in the accompanying drawings, where- 1n:
FIG. 1 is a longitudinal section of a borehole being drilled by a drilling string equipped with drill collars constructed in accordance with the present invention.
FIG. 2 is a similar, but enlarged, view showing the drilling string being lowered through the borehole, with the drill collar being shown in elevation.
FIG. 3 is a similar view after the drill bit has reached the bottom of the borehole and the drilling is started, the drill collar being shown in section to better illustrate contact of the pads with the wall of the borehole.
FIG. 4 is an enlarged cross section through the upper portion of the drill collar, taken on the line 4 4 of FIG. 3.
FIG. 5 is a similar cross section of a mid-point drill collar and taken on the line 5 5 of FIG. 3.
FIG. 6 is a fragmentary perspective view of the drill ollar, to better illustrate one of the pads and its wiping ace.
Referring more in details to the drawings:
1 designates a borehole being drilled through earth formations 2 by means of a rotary drill bit 3 which forms part of a drilling string 4. The drilling string is made up of a series of stands of drill pipe interconnected by customary tool joints whereby the stands of drill pipe are connected and disconnected when running in and pulling of the drilling string as for changing drill bits and the like.
Connected into the driling string 4 between the lowermost drill pipe 5 and the drill bit 3 are one or more drill colla-s 6 constructed in accordance with the present invention. In the present illustration, a long drill collar 6 is used with an upper shorter drill collar 7 (FIG. l). The dril collar 6 comprises extra heavy thiekwalled pipe of circular cross section to provide a cylindrical Wall S of uniform thickness and an axial bore 9 for downllow of drilling liuid therethrough. The drill collar may or may not be of larger diameter than the drill pipe 5, the purpose being to provide weight and stilfness at the lower end of the drilling string and to provide -a stiff stem for the drill bit 3 when the full weight of the drill pipe 5' is applied to the drill bit for increasing the drilling pressure and increase the drilling rate.
As previously pointed out, drill collars bend under weight of the drill pipe until a portion thereof makes Contact with the wall of the borehole. This bending points or aims the drill bit so that it deviates from a linear course, and results in a crooked hole.
of the Also, deviation of the bit is incre-ased when the bit is drilling through dipping formations, because the stern is not rigid enough to be properly guided for holding the drill bit in a straight linear course. As above described, it is the purpose of the present invention to avoid these difficulties by providing an improved construction of the drill collars, as now to be described.
In accomplishing the invention, curvature in a drill collar is restricted to one radial direction by forming the collar with a w-arp or curvature in one direction from near the upper tool joint to near the drill bit, as clearly shown in the drawings. The drill collar 6 thus curves radially outwardly from its upper box end 10 to its midpoint 11, and then inwardly to the box end 12 which screws onto the pin 13 of the drill bit, and which provides the tool joints. Therefore, when the weight of the drill pipe is bearing on the bit, any tendency of the collar to bend under Weight will be in the outward radial direction of s-aid curvature.
In order to support the drill collar by the wall of the borehole and provide a straight guide for the drill bit, the convex side 14 is equipped with a longitudinal series of pads 15, with the pads 15 spaced apart to allow passes 16 for circumferential flow of drilling uid therebetween when the drill bit is being rotated, as later described.
Each pad 1S preferably consists of an arcuate block 17 having inner arcuate faces 18 (FIGS. 4 and 5) conforming in curvature to the circumferential face 19 of the drill collar. The outer faces 2G of the pads have a radius corresponding to the radius of the borehole being drilled by the drill bit 3. Each pad 15 has a transverse width 'in the direction of rotation slightly less than the outside diameter of the drill collar (FIGS. 4 and 5), and the retractive side edegs 21 may approach a tangent to the outer surface 19 of the drill collar, while the forward edges 22 are formed substantially on a radius from the axis of the drill collar (see FIGS. 4 and 5). Since the faces 20 constitute wiping faces operating in contact with the wall of the borehole, the faces thereof are hardened as indicated by the stippling 23 (FIGS. 4 and 5) to resist Wear of the pads through contact with the formations being drilled.
As above infered, the pads 15 are positioned on the surface of the drill collar on the convex side of longitudinal curvature and in substantially exact linear alignment with each other for attachment by welds 24 and 25. The upper and lower ends 26 and 27 of the intermediate pads 28 -are formed on relatively slight bevels, but the endmost pads 29 and 30 are formed on angles of about 15 with the drill collar, as indicated at 31 and 32, to prevent snagging when running in and out of the drill collar and to facilitate engagement of a fishing tool (not shown) when required. The wiping faces of the pads, being formed on the radius of the borehole 1 and in linear alignment with each other along the longitudinal direction of the drill collar, necessitate pads of different thickness so that the faces 20 all make contact with the Wall of the borehole, as is clearly apparent in the drawings, to compensate for the permanent curvature of the drill collar.
The drill colar thus described with the pads thereon is easily lowered through the borehole 1 made by the drill bit 3, and, in fact may be lowered through a much smaller hole diameter, indicated by the dot and dash circle designated 33 in FIG. 4.
In using the drill collars constructed as described, the box 12 of the drill collar is connected with the pin 13 of the drill bit 3 and lowered into the borehole. The pin 34 of the drill collar 7 is threaded into the box 10 of the drill collar 6, in which position the outward curvatures of the drill collars 6 and 7 are diametricaly opposed with respect to each other, yas shown in FIG. l, and in position to engage diametrically opposite sides of the borehole 1. After lowering the drill collars into the borehole, the stands 5 of drill pipe are connected with the box of the drill collar 7 and the assembly is lowered in the borehole with the connection of each stand 5 of drill pipe until the drill bit 3 is bearing on the bottom of the hole.
When the drilling string is under tension due to the weight thereof being suspended, there is ample clearance for the wiping faces 20 of the pads 28, 29 and 30.
Upon rotation of the drilling string as in conventional practice under weight of the column of drill pipe, the wiping faces of the pads are contacting the wall of the borehole and hold the rotational axis of the drill collar in the axis of the borehole. Wit-h the drilling string under rotation, the pads gyrate about the axis of the borehole, with the Wear resistant lfaces of the pads riding in contact with the wall of the borehole, to maintain the stem of the bit which constitutes the drill collars in concentric relation with the borehole, the drilling iluid being circulated downwardly through the bore 9 discharging from the bit to carry the cuttings to the top of the borehole. The upwardly flowing drilling lluid passes freely through the passes 16 between the pads without losing substantial velocity. With the pads supporting the drill collars, the drill collars are sufficiently rigid, and guided by the Walls of the borehole, to keep the drill bit from deviatin g from the vertical. It is obvious that each drill collar is loose in the hole, since it engages only one side wall, so that there is no danger of a collar becoming stuck in the hole.
If more than two drill collars are coupled into the drilling string, the curved portions are positioned circumferentially of the borehole, so that the pads contact the wall in symmetrical relation.
The drill collar 7 has the same construction as the drill collar 6, but may be of shorter length. The drill collar 7 is arranged in the drilling string so that the outward curve therein is opposed to the outward curve of the drill collar 6 to stabilize the upper end of the collar 6 and prevent crowding thereof out of the axis of the borehole.
. What I claim and desire to secure by Letters Patent is:
1. A drill collar for minimizing deviation of a lborehole being drilled by a drill bit of a drilling string which includes a column of drill pipe under rotation in the borehole, said drill collar comprising a drill pipe having ends for connection into the drilling string between the drill bit and the column of drill pipe to provide a stern for the drill bit,
said drill collar having a curvature extending longitudinally thereof to provide a convex side in the direction of a wall of the borehole and assure that any bend of the drill collar under weight of the column of drill pipe takes place in the direction of curvature, and
pads on the convex side of the drill collar `and having virtually aligning faces for wiping contact with the wall of the borehole to provide support of the drill collar substantially along the full length thereof under Weight of said column of drill pipe and to minimize bending that produces deviation of the drill bit.
2. A drill collar for minimizing deviation of a borehole as described in claim 1,
wherein the pads are of different thickness to compensate for curvature of the drill collar to align said wiping faces.
3. A drill collar for minimizing deviation of a borehole as described in claim 2, and
wherein the pads are spaced apart to provide passes therebetween for llow of drilling fluid.
4. A drill collar 4for minimizing deviation of a borehole as described in claim 1,
wherein the pads are spaced apart to provide passes therebetween for tlow of drilling fluid.
5. A drill collar for minimizing deviation of a borehole as described in claim 1,
wherein the wiping faces of said pads have a transverse curvature substantially conforming to the radius of the borehole, and
the pads are spaced apart to provide passes therebetween for ilow of drilling fluid.
6. A drill collar for minimizing deviation of a borehole as described in claim 1,
wherein the drill collar comprises a uniform thickwalled drill pipe to provide a comparatively stiii stem. 7. A drill collar for minimizing deviation of a borehole as described in claim 1,
wherein the wiping faces of said pads have a transverse width substantially equal to the outside diameter of the `drill collar. 8. A drill collar for minimizing deviation of a borehole as described in claim 7,
wherein the pads are spaced apart to provide passes therebetween for flow of drilling iluid. 9. A drilling string, including a column of drill pipe, a drill bit rotated by the column of drill pipe for drilling a borehole, thickwalled drill collars providing a substantially rigid stem connecting the drill bit with the column of drill P1196, said drill collars having a preformed curvature to provide a convex side, and
pads carried by the convex side of the collars and having wiping faces supporting the drill collars against the wall of the borehole to guide the drill bit,
said collars being positioned relatively to each other for the pads of the respective drill collars to be suplported against diametrically opposite Walls 0f the borehole.
10. A drilling string as described in claim 9,
wherein the pads on each drill collar are spaced apart to pass drilling iiuid therebetween.
References Cited UNITED STATES PATENTS 2,708,099 5/ 1955 Zublin 175--75 2,745,635 5/1956 Zublin 175-76 2,891,769 6/1959 Page et al 175-76 2,956,781 10/1960 Eastman 175--61 X 3,306,378 2/1967 Williams 175--325 20 CHARLES E. OCONNELL, Primary Examiner.