GB2083102A - Full hole drill collar and method of producing same - Google Patents

Abstract

A drill collar or stabilizer consists of a cylindrical element (16) sized just under the diameter of the drill hole and is situated either immediately above the drill bit or at spaced intervals thereabove depending upon circumstances. A drilling mud or fluid feed bore (18) is formed axially through the collar and a plurality of return drilling mud or fluid apertures extend through the length of the collar between the outer wall thereof and the wall defining the centrally located feed bore spaced and parallel therefrom. <IMAGE>

Description

SPECIFICATION Full hole drill collar and method of producing same This invention relates to new and useful improvements in drill collars or stabilizers for drill strings.

Drill collars are used basically to provide the weight to be run on the drill bit and stabilizers are provided to prevent or reduce whipping action of the drill string while it is rotating and are also used to combat deviation. Square drill collars and relatively large drill collars will alleviate deviation to some extent.

A deviated hole is any bore hole that is not drilled on a truly vertical course. Alternatively, a dog leg may be formed which is any sharp change in hole angle and is usually defined as any change in deviation greater than 1-1/2" per 100 feet in depth.

There are many theories for bore holes deviating or dog legging, but most deviated hole is caused by drilling formations which are dipped, that is, formations which are not lying parallel to the earth's surface. Without any formation dipping there will be no serious deviation or dog legging problem.

However, many oil or gas bearing formations are situated in areas where formations are dipped so that deviation and dog legging become a constant problem when drilling.

Deviation and dog legging often cause the target to be missed or cause the bore hole to inadvertently cross a lease line or the like. Furthermore, badly deviated and dog legged holes can cause problems with production equipment such as sucker rods wearing through the tubing. Deviated or dog legged hole may also result in failure of the drill pipe or drill collar connections. Serious deviation can cause the formation of a key-seat in the well bore and cause stuck pipe in the key-seat and/or increase the possibility of differentially stuck pipe. Other disadvantages include excessive casing wear which can lead to casing failure. The most costly problem as far as the industry is concerned, is the reduction in penetration rate caused by reducing bit weight while attemping to control deviation.

Specially designed drill collars and the like have been used in the past in an attempt to stiffen the lower portion of the drill string thereby reducing the tendency for the bitto deviate or to dog leg. Such drill collars may include what are known as square drill collars which have a substantially square cross section. Several drill collars are normally screwed together to form a drill string. Where deviation is a problem, stabilizers with radially extending fins or vanes or with spiral blades or with non-rotating blades or a combination of the aforementioned, may be added to the drill collar string to combat deviation. Roller reamers may also be added to the bottom hole assembly.

The construction of drill collars and stabilizers in these various shapes and configurations are necessary because of the requirement of providing annular clearance between the drill collar or stabilizer and the wall of the drill bore to act as the return path for the drilling mud together with the chips carried thereby.

However, such devices are unsatisfactory for many reasons, the principal one of which is that when passing through soft formations such as shale sections, the shale is aggravated due to the scraping effect of the sharp corners upon the soft surface of the bore hole which often causes collapse of the bore hole or at least an overloading of the drilling mud return system. Furthermore, if such a condition is encountered, then the stiffening effect of such drill collars or stabilizers is reduced due to the hole enlargement.

The same faults occur with the integral blade stabilizers and spiral type stabilizers.

The blades of the non-rotating blade stabilizers are manufactured from hard rubber which can distort under pressure or, alternatively, can dig into a soft shale formation. In either circumstances, the stiffness of the assembly is reduced and the tendency of the drill bit to deviate is increased.

As mentioned previously, the tendency to deviate or dog leg is caused primarily by formation dip so that under circumstances where there is little or no formation dip, there will be little or no tendency for the hole to deviate.

Under such circumstances, it is common to use what is called a "slick bottom hole assembly". This assembly consists of normal drill collars connected together with a bit and sometimes with a shock sub situated just above the bit. If deviation does become a minor problem, it is common practice in shale areas to continue with the "slick bottom hole assembly" and to merely reduce the weight on the bit and possibly increase the rotary speed slightly.

However, the end result is a slower rate of penetration and therefore is more costly. It is also common practice to run this type of assembly in areas where shale sloughing is a problem because conventional stabilizers and reamers tend to aggravate shales because of the gouging and scraping action which occurs.

In directional work, as in any other deviated hole, when it is desired to reduce angle, it is common practice to run a "pendulum assembly" and reduce weight on the bit. However, if a directional driller has the bit heading in the desired angle, he may run a stiff bottom hole assembly which will maintain angle and direction as desired and run a considerable amount of weight on the bit.

As mentioned previously, one of the best methods of combatting deviation and dog leg misalignment is to use what is known as the "packed hole assembly", such as the square drill collar which is in common use. However, the principal disadvantage is the sloughing which occurs particularly in shale or soft formations.

Obviously, a full guage tool or collar having a smooth uninterrupted outer surface would offer the best solution, but unfortunately little or no room is provided between the outer surface and the wall of the bore hole for the return of the drilling fluid together with the chips carried thereby, and attempts to approach this solution such as the use of a seven-inch diameter drill collar in an eight and a half inch hole or a ten-inch drill collar in a twelve and a quarter inch hole tends to cause erosion in the soft sections because of the high annular velocities of the return drilling fluid due to the restricted annular space.

The present invention overcomes disadvantages inherent with such a solution and also disadvantages found with the use of conventional drill collars and stabilizers by providing what may be termed a full hole drill collar or stabilizer with the minimum clearance between the smooth outer surface thereof and the wall of the bore hole and at the same time providing one or more vertical bores through the collar or stabilizer for the return of the drilling mud or fluid and the chips carried thereby, it being understood that the centre of the collar is axially bored as at present, to act as the downward feed channel for the drilling mud.

In accordance with the invention there is provided a full hole drill collar or stabilizer for drill strings comprising a cylindrical element, a fishing neck formed on each end of said element reducing in diameter from the end of said element to the distal end of said fishing neck, a centrally located drilling fluid feed bore extending axially through said element from adjacent one end to adjacent the other end, at least one drilling fluid return passage extending through said element from one end to the other, spaced and parallel to said feed bore and opening out onto said fishing neck into the ends thereof and means at either end of said element to detachably secure same in series within a drill string, said drilling fluid return passage being milled into the outer wall of said element along the majority of the length thereof and an arcuately curved cover plate enciosing the length of said passage with the ends of said passage being open, said milled wall and said cover plate defining said drilling fluid return passage, and means to secure said cover plate in position.

It should be understood that the term "full hole drill collar" means a collar or stabilizer having a diameter as close to the bit size as possible, but of course having a diameter just slightly less in order to alleviate any excessive tendency to stick in the hole.

The clearance between the outer surface of the drill collar and the wail of the bore hole would be controlied by the drilling parameters and the down hole conditions encountered.

Also in accordance with the invention there is provided a method of forming a full hole drill collar for drill strings, from a cylindrical element, consisting of the steps of forming a driliing fluid feed bore axially through said element from one end to the other, forming a fishing neck on each end of said element, forming a tapered junction between each end of said central section and the fishing neck formed thereon, forming at least one drilling fluid return passage through said element spaced and parallel to said feed bore and opening out onto the tapered junction at each end and then forming drill string attaching means in each end of said fluid feed bore.

Another advantage of the present invention is that it can be provided in any desired lengths once again depending upon conditions from, for example, one foot to fifty feet or more with a preferred length being in the neighborhood of thirty feet for a full hole drill collar.

Another advantage of the invention is the fact that it is easily connected in series with the drill string by conventional screw coupling means and can be situated at any desired location upon the drill collar portion of the drill string once again depending upon down hole conditions and operating conditions.

Still another advantage of the present invention is to provide a device of the character herewithin described which is simple in construction, economical in manufacture and otherwise well suited to the purpose for which it is designed.

Figure lisa partially schematic cross sectional representation of part of the lower end of a bore hole with one embodiment of the invention incorporated within the drill string shown schematically.

Figure 2 is a top plan view of the full hole drill collar or stabilizer per se.

Figure 3 is a front elevation of a full hole drill collar with spiral grooves on the outer surface thereof.

Figure 4 is a side elevation of an alternative embodiment.

Figure 5 is an end view of Figure 4.

Figure 6 is a side elevation of the preferred embodiment with the cover plates removed.

Figure 7 is an end view of Figure 6.

Figure 8 is an enlarged fragmentary end view of Figure 6 showing the method of preparing the passageway to receive the cover plate.

Figure 9 is a fragmentary isometric view of one of the cover plates per se.

Figure 10 is an end view of Figure 6 with the cover plates installed.

Figure 11 is a view similar to Figure 6, but showing an alternative method of construction.

Figure 12 is an end view of Figure 11.

Figure 13 is a side elevation of Figure 11 with the sleeve in position.

Figure 14 is a partially schematic end view showing one method of holding the sleeve in position.

Figure 15 is a side elevation of an alternative embodiment showing further method of holding the sleeve in position.

Figure 16 is a view similar to Figure 15 but showing a further method of holding the sleeve in position.

Figure 17 is a view similar to Figure 14 but show- ing alternative methods of holding the sleeve in position.

Figure 18 is a fragmentary end elevation showing a further embodiment.

Figure 19 is a side view of the embodiment shown in Figure 18.

In the drawings like characters of reference indicate corresponding parts in the different figures.

Proceeding therefore to describe the invention is detail, reference character 10 illustrates schematic, cally, the lower end of a bore hole with a conventional bit 11 being situated at the lower end of the drill string collectively designated 12 of which a conventional relatively smali diameter drill collar 13 forms part thereof, and the invention collectively designated 14 is serially connected between the lower end of the drill collar 13 and the upper end 15 of the drill bit assembly 11.

The invention 14 consists of an elongated cylindri cal element 16 preferably having a smooth outer perimetrical wall surface 17 which is continuous in the preferred embodiment.

A centrally located axial bore 18 is formed through the element 16 from one end to the other and a screw threaded connection 19 is provided at either end of this bore as clearly shown, to act as a conventional screw threaded connection between the lower end of the drill collar 13 at the upper end thereof and the upper end 15 of the drill bit assembly at the lower end thereof.

The centrally located bore 18 then communicates with the corresponding bore 18' in the conventional drill collar 13 and the drill fluid circulating system indicated by reference character 20 in the drill bit assembly 11. This bore 18 therefore acts as a drilling fluid feed bore through the element 16.

The diameter of the element 16 is just slightly less than the diameter of the drill bit 11 and hence just slightly less than the diameter of the drill bore 10 as clearly shown and thus acts as a stabilizing influence and stiffener to the drill string.

Means are provided to act as a return for the drilling fluid and drilling chips, said means taking the form of at least one return bore 21 formed through the element 16 from one end to the other end parallel to the feed bore 18 but spaced between the outer peripheral wall 17 of the element and the wall 22 defining the central feed bore 18. In practice and in orderto provide balance, a plurality of symmetrically situated return bores are desirable.

It is preferred that a plurality of such return bores 21 be provided depending upon the diameter of the element and the strength of the material used to form same, it being understood that when used as a drill collar as illustrated in Figure 1, it can also add weight to the system as is conventional.

The total cross sectional area of the return bores 21 should preferably be greater than the cross sectional area of the feed bore in order to prevent any restriction to the return of the drilling fluid together with the drill chips carried thereby.

As mentioned previously, the length of the element 16 will depend upon design parameters and may be as little as one foot or as long as fifty feet or more and although it is shown as a drill collar situated immediately above the drill bit assembly 11, nevertheless full hole drill collars may be situated at spaced intervals above the drill bit depending upon bore hole conditions and drilling characteristics.

It will also be appreciated that one or more collars such as that illustrated by reference character 14 can be placed one above the other to provide an elongated support length or stiffening to the drill string assembly.

The advantages of this construction include the improvements gained by having the full hole drill collar as close to the bit size as is possible depending upon conditions although if excessive rotary torque or excessive tendency to stick occurs, the clearance will have to be increased. However, as mentioned previously, the collar would essentially be a full gauge tool with the advantage that there would be virtually no annular space between the collar or stabilizer and the wall of the bore hole which might allowthe bit to deviate.

Because of this and the resistance to deviation, the optimum bit weight can be approached so that higher rates of penetration may be obtained compared to other methods of handling deviated hole problems.

Because of the smooth outer surface of the present invention, scraping or damage to the wall of the bore hole particularly in soft sections is reduced if not eliminated and erosion due to high velocities of return drilling fluid through narrow annular spaces is also eliminated.

As mentioned previously, integral blade, welded blade, replaceable wear pad stabilizers and square drill collars all tend to gouge and scrape shales and other soft formations and the only stabilizing tool presently available which does not tear up soft formations is the non-rotating rubber blade stabilizer, the blades of which tend to bend and fail under moderate to severe lateral loads caused either by lateral formation forces or buckling ofthe drill collar column.

By contrast, because of the maximum wall contact of the present invention, there is resistance to deviation without untoward damage to the bore hole wall.

If relatively long lengths of full drill collar provide a tendency of sticking, then spiral grooves 23 as shown in Figure 3, can be provided to reduce this tendency but these would not act as return ports for the drilling fluid so that no washing or erosion would occur.

However, some drilling fluid would probably escape up the annular space between the spiral grooves and the wall of the bore hole. This would probably occur also without spiral grooves and would depend upon: 1) diameterofthe return ports.

2) resistance to flow between the outer diameter of the full hole drill collar and the wall of the bore hole.

3) resistance to flow within the return ports.

4) bottom hole pressure.

In practice, it would be desirable to have some fluid going up the outer diameter of the full hole drill collar to provide lubrication and cooling of the tooi.

This would not be detrimental to soft formations as long as the ascending velocity of said fluid was not excessive.

Figure 4 shows an embodiment similar to that illustrated in Figure 1 in which four bores or passageways 21 are formed through the element equidistantly arranged around the central bore 18 and it will be noted that a fishing neck 24 is formed on each end of the element 14 with a tapered junction 25 extending between the inner end of the fishing neck and each end of the central section of the element identified by reference character 26. The screw threaded portion 19 at each end of the fluid feed bore 18 permits attachment of the drill string at either end as hereinbefore described.

Figures 6 to 19 show the preferred embodiment which may be formed either by milling or forging or a combination of the two methods.

In Figure 6 to 10, the element collectively designated 14 is cylindrical and the fishing necks 24 are formed at each end with the tapered shoulder or connection 25 extending between the inner ends of the fishing necks and the centre section 26.

A passageway 27 is milled in the outer surface of the centre section and extends to open out on the tapered surfaces 25. In the present embodiment illustrated, four such passageways are provided equidistantly spaced around the perimeter or circumference of the centre section and the cross sectional area of these passageways is preferably simi larto that shown in Figure 8.

The passageways extend into the element and terminate with bases 28 which are spaced outwardly from the walls of the central feed bore 18 is clearly shown.

The upper longitudinal extending corner portions 29 of the walls of the passageway are then chamfered as illustrated by reference character 30 in Figure 8 and an arcuately curved longitudinally extending cover plate 31 is formed with the outer edge 32 also being chamfered so that when the cover plate engages upon the upper side of the passageway, the chamfered edges 32 match the chamfered edges 30.

Furthermore, the radius of curvature of the cover plates is the same as the radius of curvature of the central section 26 of the element. Once the cover plates have been installed, various methods are provided to maintain same in position. In Figure 10, a weld fillet 33 is used to fill in the longitudinally extending V-shaped grooves on either side of the cover plates so that once the cover plates are welded in positiOn, the passageway 27 is enclosed with the exception of the ends which are open and which open out onto the sloping or tapered junctions 25 between the central section 26 and the fishing necks 24. These provide the return passageways hereinbefore described and the cross sectional area of these passageways should be at least equal to and preferably greater than the cross sectional area of the fluid feed bores 18.Furthermore, if desired, the outer surface of the cover plates may be hard faced by conventional methods and spiral grooves similar to those shown in Figure 3 may be provided, if desired.

Figures 11, 12 and 13 show a further method of construction and embodiment of the enclosing of the passageways 27. Once the passageways have been milled or otherwise formed into the outer wall of the element, once again opening out onto the tapered junctions 25, the remaining outer surface of the centre section of the element is turned down or otherwise formed, to provide a shoulder 34 adjacent one end 35 of the centre section whereupon a cylindrical sleeve 36 is engaged over the centre section and abuts against the shoulder as clearly shown in Figure 13. It is preferable that this sleeve or casing be shrunk into position over the element and it will be observed that the outer diameter of the sleeve is the same as the outer diameter of the end 35 of the centre section as shown in Figure 13.

Figures 14 through 17 show various methods of securing the shell sleeve or casing into position once it has been installed as hereinbefore described. Figure 14 shows a plurality of rows of set screws 37 engaged within recesses 38 formed through the casing with the set screws screw threadably engaging the portions of the centre section between the return passageways 27 so that the outer surfaces of the heads of the set screws 37 are flush with or preferably recessed relative to the outer surface 39 of the sleeve. Once again this sleeve may be hard faced and/or formed with spiral grooves similar to that illustrated in Figure 3.

Figure 15 shows a screw threaded ring 40 screw threadably engaging the opposite end 35A of the centre section which is correspondingly screw threaded to receive this ring. This clamps the sleeve 36 against the shoulder 34 with the outer diameter of the ring being no largerthan the outer diameter of the sleeve as clearly shown.

Alternatively, an annular groove 41 may be formed around the end 35A of the centre section and a snap ring engaged within the groove and against the opposite end of the sleeve once again holding the casing 36 firmly against the shoulder 34. In all cases, it will be observed that the passages 27 extend beyond the sleeve and open out onto the sloping or tapered connections 25 so that the sleeve together with the walls of the milled or otherwise formed passage, form enclosed passageways with open ends, for the return of drilling fluid and the like as hereinbefore described.

Figure 17 shows a yet further method of securing the casing or sleeve in position with reference characters 42 illustrating wedging pins engaging within tapered apertures 43 through the sleeve and into the body of the centre section, reference character 44 showing screw threaded set screws and reference character 45 showing cover plates once again held in position with set screws 44. In all cases, the outer surfaces of the set screws or pins are flush with or below the outer surface 39 of the casing 36.

Figures 18 and 19 show a still further method of closing off the milled or otherwise formed passages 27 formed longitudinally through the centre section in spaced and parallel relationship to the central bore or main fluid feed bore 18.

In this particular embodiment, a pair of slots 46 are formed in the side walls 47 of the passages 27 spaced slightly inwardly from the outer surface 48 of the element with the edges of the slots or grooves being rounded slightly to prevent galling from occurring.

A longitudinally extending arcuately curved plate 49 is formed with a radius less than the radius of the element and this cover plate is slid into the grooves from one end of the element and abuts a shoulder 50 at the other end formed by the termination of the grooves just prior to the end 35 of the centre section.

This cover plate may be held in position by any of the methods hereinbefore described and it will be observed that the longitudinal central portion 49A of the cover plate is substantially coincident with the curved outer surface of the element if same was continued across the passageway 27 as shown in phantom in Figure 18 and this area may be surface har- dened and/or spiral as hereinbefore described.

The method of manufacture of the various embodiments may be either by milling or forging or a combination of both with the various cover strips such as 31 or49 being cut from a length of drill casing having the required diameter.

Furthermore, the sleeve 36 may be cut from a length of drill casing having the desired diameter.

It will be appreciated that the various constructions, methods, and attaching means described and illustrated for specific embodiments may be interchanged and adapted one with the other as desired.

Claims (21)

1. A full hole drill collar or stabilizer for drill strings comprising a cylindrical element, a fishing neck formed on each end of said element reducing in diameter from the end of said element to the distal end of said fishing neck, a centrally located drilling fluid feed bore extending axially through said element from adjacent one end to adjacent the other end, at least one drilling fluid return passage extending through said element from one end to the other, spaced and parallel to said feed bore and opening out onto said fishing neck into the ends thereof and means at either end of said element to detachably secure same in series within a drill string, said drilling fluid return passage being milled into the outer wall of said element along the majority of the length thereof and an arcuately curved cover plate enclosing the length of said passage with the ends of said passage being open, said milled wall and said cover plate defining said drilling fluid return passage, and means to secure said cover plate in position.

2. The device according to Claim 1 in which the cross sectional area of said return passage is at least equal to the cross sectional area of said feed bore.

3. The invention according to Claims 1 or 2 in which the outer peripheral wall of said element is smooth and uninterrupted.

4. The device according to Claims 1,2 or3 which includes a plurality of return passages formed through said element equidistantly spaced around said feed bore and being situated parallel thereto.

5. The device according to Claims 1, 2 or 4 which includes means on the surface of the outer peripheral wall of said element to reduce differential sticking of said collar within the drill bore.

6. The invention according to any of the preceding claims in which said drilling fluid return passage comprises a bore formed through said elements spaced inwardly from the outer surface of said element.

7. The invention according to Claim 4 in which said drilling fluid return passage is milled into the outer-wall of said element along the majority of the length thereof and an arcuately curved cover plate enclosing the length of said passage with the ends of said passage being open, said milled wall and said cover plate defining said drilling fluid return passage, and means to secure said cover plate in position.

8. The invention according to Claim 7 in which said means to secure said cover plate in position include a shoulder formed around said element on the central portion thereof adjacent the junction of said central portion to one of said fishing necks, a cylindrical sleeve engaging around said central portion and abutting said shoulder by one end thereof, and means to secure said sleeve in position.

9. The invention according to Claim 8 in which said last mentioned means includes set screws operatively engaging through said sleeve and into said element, the heads of said set screws being at least flush with the outer surface of said sleeve.

10. The invention according to Claim 8 in which said last mentioned means includes a screw threaded retaining ring screw threadably engaging the other end of said central section, the outer surface of said retaining ring being flush with or below the outer surface of said sleeve.

11. The invention according to Claim 8 in which said last mentioned means includes a groove formed around said central section adjacent the other end thereof and a snap ring operatively engaging said groove and the adjacent end of said sleeve.

12. The invention according to Claim 8 in which said last mentioned means includes at least one retaining plate engaging said other end of said central section flush with or below the outer surface of said sleeve and engaging the adjacent end of said sleeve and means detachably securing said retaining plate in position.

13. The invention according to Claim 8 in which said last mentioned means includes a pair of casing retaining grooves formed in the sides of said walls of said centre section which defines said passages, and spaced inwardly from the outer surface of said element and extending from one end of said passage to adjacent the other end thereof, thereby defining a stop at said other end, and an arcuately curved cover plate slidably engageable within said slots and engaging said stop, the diameter of the curvature of said cover plate being greater than the diameter of said element and means to secure said cover plate in position.

14. A method of forming a full hole drill collar for drill strings, from a cylindrical element, consisting of the steps of forming a drilling fluid feed bore axially through said element from one end to the other, forming a fishing neck on each end of said element, forming a tapered junction between each end of said central section and the fishing neck formed thereof, forming at least one drilling fluid return passage through said element spaced and parallel to said feed bore and opening out onto the tapered junction at each end and then forming drill string attaching means in each end of said fluid feed bore.

15. The method according to Claim 14 in which the cross sectional area of said return passage is at least equal to the cross sectional area of said feed bore.

16. The method according to Claims 14 or 15 which includes the additional step of forming a plurality of drilling fluid return passage around said feed bore equidistantly spaced therefrom.

17. The method according to Claims 14, 15 or 16 in which said passageway consists of bores formed through said element spaced inwardly from the outer surface of said element.

18. The method according to Claim 14 in which the forming of said passageway consists of the steps of forming a passageway in the outer wall of said element along the majority of the length thereof and then securing an arcuately curved cover plate over said passage to enclose said passage with the ends thereof being open.

19. The method according to Claim 18 which includes the additional step of securing said arcuatelycurved cover plate by first forming a shoulder around said element on the central portion thereof adjacent the junction of said central portion to one of said fishing necks, and then engaging a cylindrical sleeve around said central portion and abutting one end of said cylindrical sleeve against said shoulder and then securing said sleeve in position.

20. A full hole drill collar and method of producing same substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

21. A full hole drill collar or stabilizer for drill strings comprising a cylindrical element, a fishing neck formed on each end of said element reducing in diameter from the end of said element to the distal end of said fishing neck, a centrally located drilling fluid feed bore extending axially through said element from adjacent one end to adjacent the other end, at least one drilling fluid return passage extending through said element from one end to the other, spaced and parallel to said feed bore and opening out onto said fishing neck into the ends thereof and means at either end of said element to detachably secure same in series within a drill string.