CA1253846A - Method for improving cuttings removal in drilling deviated wellbores - Google Patents
Method for improving cuttings removal in drilling deviated wellboresInfo
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- CA1253846A CA1253846A CA000496078A CA496078A CA1253846A CA 1253846 A CA1253846 A CA 1253846A CA 000496078 A CA000496078 A CA 000496078A CA 496078 A CA496078 A CA 496078A CA 1253846 A CA1253846 A CA 1253846A
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- borehole
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- drill string
- jets
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Abstract
METHOD FOR IMPROVING CUTTINGS REMOVAL
IN DRILLING DEVIATED WELLBORES
ABSTRACT
A rotary drilling technique for improving cuttings removal and reducing packoff and differential pressure sticking tendencies of drill strings in deviated wellbores employs a number of jets of drilling fluid which emerge from the drill string preferably near the bit in a direction axially along the borehole away from the drill bit or at specific locations up the drill string where casing size increases because of the use of a liner. The jets may be arranged to emerge entirely axially up the borehole or with an additional, radial component of velocity also. Because packoff problems generally arise in the regions where the radial width of the annulus increases, the jets are to be provided in these regions in order to maintain linear fluid velocities as well as providing additional fluid volume in this region. The drilling tool comprises a tool joint with a number of angled, radial passageways pointing in a reverse direction uphole so that the emerging fluid jets have the required components of velocity.
IN DRILLING DEVIATED WELLBORES
ABSTRACT
A rotary drilling technique for improving cuttings removal and reducing packoff and differential pressure sticking tendencies of drill strings in deviated wellbores employs a number of jets of drilling fluid which emerge from the drill string preferably near the bit in a direction axially along the borehole away from the drill bit or at specific locations up the drill string where casing size increases because of the use of a liner. The jets may be arranged to emerge entirely axially up the borehole or with an additional, radial component of velocity also. Because packoff problems generally arise in the regions where the radial width of the annulus increases, the jets are to be provided in these regions in order to maintain linear fluid velocities as well as providing additional fluid volume in this region. The drilling tool comprises a tool joint with a number of angled, radial passageways pointing in a reverse direction uphole so that the emerging fluid jets have the required components of velocity.
Description
~z5~
METHOD FOR IMPROVING CUTTINGS REMOVAL
IN DRILLING DEVIATED WELLBORES
The present invention relates to the drilling of boreholes, particularly deviated boreholes into the earth by the rotary drilling technique. It is particularly directed to a method of this kind which has an improved capability for removing the drill cuttings formed during the drilling process and of mitigating the problems of differential pressure sticking of the drill string and of packoff in the borehole upon removal of the drill string.
The rotary drilling technique is the most common method used for drilling boreholes into the earth to reach subterranean formations containing oil, gas and other minerals. In the rotary drilling technique, a drilling rig at the surface rotates a drill string which is made up of lengths of drill pipe, together with drill collars and a drill bit at the bottom end of the drill string. The drill pipe is made up of a series of "joints" or sections of seamless pipe which are serially connected, end to end by means of connectors known as tool joints. The drill pipe serves to transmit torque from the drilling rig to the bit and, in addition, to provide a passage for the drilling fluid or drilling "mud" from the surface to the bit. The drilling mud is circulated by means of a mud pump at the drilling rig which takes in mud from a mud supply and circulates it down the inside of the drill string to the bit. At that point, the mud comes out around the bit and returns to the surface through the annulus formed between the outside of the drill string and the walls of the borehole/liner/casing. At the surface, the drilling mud is treated to remove the drill cuttings and then recirculated through the system.
The drill collars are, essentially, thick-walled sections of pipe, relatively thicker than drill pipe which act as stiff members in the drill string and are normally installed in the drill string immediately above the bit in order to supply weight on the lX53~46 bit and to maintain the drill string in a state of tension. In common rotary drilling techniques, the lower portion of the drill collars will be in axial compression to provide the weight on bit while the top portion of the drill collars may be in tension. The drill collars will normally be of a larger diameter than the drill pipe in use and normally will be about 10 to 25 cm (approx. 4 to 10 inches) in outside diameter. Heavy weight drill pipe, i.e., drill pipe having a greater wall thickness than normal pipe may be used to connect the drill collars to the rest of the pipe string so as to provide greater stiffness and additional weight in this portion of the string. The transition point from compression to tension may be in the heavy weight pipe portion of the string.
Usually, a large drill bit diameter is used near the surface. After drilling to a certain depth, the drill bit is removed and a pipe having a diameter smaller than the borehole is inserted to form a casing. Drilling is resumed with a smaller drill bit and thereafter the insertion of a smaller casing pipe into the borehole. The smaller casing pipe may not extend to the surface and is called a liner in such a case. This procedure is repeated until an oil formation is reached. As a result, the diameters of the casings and/or liners decrease as penetration into the earth increases. In other words, the annular areas between the casing and the drill string may decrease in diameter as one travels downward from the surface of the earth to the drill bit.
Well boreholes may be drilled into the earth at angles in which the general direction of the well deviates from the vertical.
This is normally referred to as directional drilling and is particularly useful in offshore production where it may be desirable to complete a number of deviated wells from a single drilling location. Recent developments have enabled directional drilling techniques to be used for ultra high angle boreholes having ultimate deviations greater than 60 from the vertical or for producing complicated wellbore profiles.
A problem which is frequently encountered in directional drilling, particularly in the drilling of ultra high angle boreholes -- although it is by no means so limited -- is that the cuttings formed by the drill bit tend to settle and compact on the low side oF the borehole and may be difficult to pick up by the return flow of drilling mud in the annulus when the flow commences again. This is particularly troublesome when the flow of drilling mud is stopped, for example, when a new joint of pipe is being added to the drill string. The problem is compounded by the flow patterns of the mud around the drill string. In a high angle borehole, for example, the drill string tends to lie on the bottom of the hole and because the cuttings also tend to settle on the bottom of the hole, the drill string rotates in a bed of cuttings. In porous formations, this tends to create the problem of differential pressure sticking, as mentioned in U.S. Patent No. 4,368,787.
An additional problem which is encountered is that of "packoff" of the annulus when the drill string is to be withdrawn or pulled up from the borehole. In this case, the withdrawal of the Iarge diameter drill collars along the borehole tends to pack the drill cuttings tightly against one another to form an almost solid mass that makes further movement of the drill string difficult.
This problem is aggravated by the tendency of the drill cuttings to settle out of the drilling fluid immediately above the drill collars, at the point where the velocity of the drilling mud decreases by reason of an increase in the cross-sectional area of the annulus where the large diameter drill collar is joined to the relatively narrower drill pipe or in upper portions of the wellbore where the casing increases in diameter.
U.S. Patent No. 4,361,193 describes a method for mitigating the differential pressure sticking of the drill string and for improving cuttings removal during deviated, rotary drilling. In this technique, the drill cuttings which accumulate on the lower side of the wellbore are swept into the main return stream of the drilling mud flow by the use of radial jets of fluid which are :l~S~4~
projected outwards from the lower portion of the drill string.
These jets impart a stirring movement to the cuttings which settle on the low side of the wellbore and facilitate their removal by the mud which is flowing axially along the annulus. This technique mitigates the problems of differential pressure sticking and cuttings removal to a substantial extent but, because the radial fluid jets are provided in the enlarged portion of the drill string, it does not wholly solve the problems arising from the reduction in mud velocity at the points where the width of the annulus increases.
U. S. Patent No. 4,368,787 discloses a device for reducing the pressure differential sticking of the drill string and for providing improved removal of drill cuttings by using reverse circulation of the drilling mud. The drill bit used in this technique has an internal mud pump which is driven by the bit cones and this pump is used to pump the mud from the annulus, around and through the bit and up the drill pipe in a direction opposite to the normal one. Although this device will obviously mitigate the problems of differential pressure sticking, since there are no drill cuttings in the annulus, it is not entirely free -From this problem because the solid components of the drilling mud are still present and may, in certain circumstances, create a differential sticking problem. In addition, the device would be expensive to fabricate and maintain in normal use because the mud pump components would be subject to a severe degree of abrasion in use from the drill cuttings passing through it.
It would therefore be desirable to have a technique for alieviating the problems described above which did not require the use of complicated downhole apparatus.
The present inventor has now devised a technique for mitigating the problems of cuttings removal and differential pressure sticking in drill strings used in the rotary drilling method. Also, the technique mitigates the problem of cuttings removal between the drill string and casing/liner where the casing 3LZS~ 6 diameter increases. In addition, the technique mitigates the additional problem of "packoff" in the annulus when the drill string is to be withdrawn from the wellbore. The technique is particularly applicable to directional drilling operations, especially in highly deviated boreholes but it is by no means limited to such use. It may be used, if necessary, in conventional, vertically-drilled boreholes if conditions should make it necessary or desirable to do so .
It has been found that if the drilling mud which is passing down the drill string is projected outwards through flow passages in the lower portion of the drill string to form upwardly directed jets, the removal of the drill cuttings will be facilitated and the problems described above substantially mitigated. The upwardly directed jets may suitably be provided by appropriately directed flow passages or nozzles in the drill collars, heavy weight pipe joints or in other, special tool joints in the drill string, where required.
According to the present invention, the method of rotary drilling a borehole, particularly a deviated borehole, into the earth uses a drill string through which the drilling fluid is circulated, a portion of the drilling fluid being passed through flow passages in various portions of the drill string to form jets of drilling fluid having a component of velocity which is directed axially along the borehole in a direction away from the drill bit.
Generally, this will be in an upward direction but in highly deviated holes it will be more "backward" than "upward", although similar considerations will still apply.
The apparatus for drilling by this technique comprises a drilling tool for insertion into the drill string, generally into the lower portion of the string in the proximity of the drill bit or at any location where there is an increase in the radial width of the annulus defined by the outside of the drill string and the walls of the borehole or the casing, this tool being characterized by a number of fluid flow passages which extend from a central, axial \
`` 1.~2~3~'~6 : - 6 ~
passageway in the tool (provided for circulati~n of the drilling mud to the bit) to the exterior of the tool for creating jets of drilling fluid having a component of velocity directed axially along the borehole away from the drill bit, as described above. The drilling tool may be generally in the form of a drilling collar, a joint of heavy weight pipe or it may be incorporated into a specialized tool joint used to connect one section of the drill string to another. The drilling tool is preferably located on the angular shoulder of a lower tool joint, at the point where the width of the annulus increases, so that the axially directed jets of drilling mud help to provide additional fluid volumes and maintain the linear ~luid velocities in this region.
The present invention, then, in one aspect, resides in a method of effecting removal of cuttings resulting fram drilling a borehole into the earth by rotary drilling, which comprises using a drill string comprising serially connected sections of drill pipe through which drilling fluid is circu-lated and at the end of which is a drill bit, in which a portion of the drilling fluid is passed through apertures in at least one portion of the drill string to form ~ets of drilling fluid having a camponent of velocity which is directed axially along the borehole and in a direction away fram the drill bit, and wherein the apertures are provided in the drill string in regions where the radial width of the annulus defined by the outside of the drill string and the walls of the borehole or casing increases.
In another aspect, this invention resides in an apparatus for effecting removal of cuttings resulting from drilling into the earth b~y rotary drilling using a drill camprising serially connected sections of drill pipe through which drilling fluid is circulated and at the end of which is a drill bit, camprising:
(1) a tool for insertion into portions of the drill string, B
~ 2S;~ 6 - 6(a) -
METHOD FOR IMPROVING CUTTINGS REMOVAL
IN DRILLING DEVIATED WELLBORES
The present invention relates to the drilling of boreholes, particularly deviated boreholes into the earth by the rotary drilling technique. It is particularly directed to a method of this kind which has an improved capability for removing the drill cuttings formed during the drilling process and of mitigating the problems of differential pressure sticking of the drill string and of packoff in the borehole upon removal of the drill string.
The rotary drilling technique is the most common method used for drilling boreholes into the earth to reach subterranean formations containing oil, gas and other minerals. In the rotary drilling technique, a drilling rig at the surface rotates a drill string which is made up of lengths of drill pipe, together with drill collars and a drill bit at the bottom end of the drill string. The drill pipe is made up of a series of "joints" or sections of seamless pipe which are serially connected, end to end by means of connectors known as tool joints. The drill pipe serves to transmit torque from the drilling rig to the bit and, in addition, to provide a passage for the drilling fluid or drilling "mud" from the surface to the bit. The drilling mud is circulated by means of a mud pump at the drilling rig which takes in mud from a mud supply and circulates it down the inside of the drill string to the bit. At that point, the mud comes out around the bit and returns to the surface through the annulus formed between the outside of the drill string and the walls of the borehole/liner/casing. At the surface, the drilling mud is treated to remove the drill cuttings and then recirculated through the system.
The drill collars are, essentially, thick-walled sections of pipe, relatively thicker than drill pipe which act as stiff members in the drill string and are normally installed in the drill string immediately above the bit in order to supply weight on the lX53~46 bit and to maintain the drill string in a state of tension. In common rotary drilling techniques, the lower portion of the drill collars will be in axial compression to provide the weight on bit while the top portion of the drill collars may be in tension. The drill collars will normally be of a larger diameter than the drill pipe in use and normally will be about 10 to 25 cm (approx. 4 to 10 inches) in outside diameter. Heavy weight drill pipe, i.e., drill pipe having a greater wall thickness than normal pipe may be used to connect the drill collars to the rest of the pipe string so as to provide greater stiffness and additional weight in this portion of the string. The transition point from compression to tension may be in the heavy weight pipe portion of the string.
Usually, a large drill bit diameter is used near the surface. After drilling to a certain depth, the drill bit is removed and a pipe having a diameter smaller than the borehole is inserted to form a casing. Drilling is resumed with a smaller drill bit and thereafter the insertion of a smaller casing pipe into the borehole. The smaller casing pipe may not extend to the surface and is called a liner in such a case. This procedure is repeated until an oil formation is reached. As a result, the diameters of the casings and/or liners decrease as penetration into the earth increases. In other words, the annular areas between the casing and the drill string may decrease in diameter as one travels downward from the surface of the earth to the drill bit.
Well boreholes may be drilled into the earth at angles in which the general direction of the well deviates from the vertical.
This is normally referred to as directional drilling and is particularly useful in offshore production where it may be desirable to complete a number of deviated wells from a single drilling location. Recent developments have enabled directional drilling techniques to be used for ultra high angle boreholes having ultimate deviations greater than 60 from the vertical or for producing complicated wellbore profiles.
A problem which is frequently encountered in directional drilling, particularly in the drilling of ultra high angle boreholes -- although it is by no means so limited -- is that the cuttings formed by the drill bit tend to settle and compact on the low side oF the borehole and may be difficult to pick up by the return flow of drilling mud in the annulus when the flow commences again. This is particularly troublesome when the flow of drilling mud is stopped, for example, when a new joint of pipe is being added to the drill string. The problem is compounded by the flow patterns of the mud around the drill string. In a high angle borehole, for example, the drill string tends to lie on the bottom of the hole and because the cuttings also tend to settle on the bottom of the hole, the drill string rotates in a bed of cuttings. In porous formations, this tends to create the problem of differential pressure sticking, as mentioned in U.S. Patent No. 4,368,787.
An additional problem which is encountered is that of "packoff" of the annulus when the drill string is to be withdrawn or pulled up from the borehole. In this case, the withdrawal of the Iarge diameter drill collars along the borehole tends to pack the drill cuttings tightly against one another to form an almost solid mass that makes further movement of the drill string difficult.
This problem is aggravated by the tendency of the drill cuttings to settle out of the drilling fluid immediately above the drill collars, at the point where the velocity of the drilling mud decreases by reason of an increase in the cross-sectional area of the annulus where the large diameter drill collar is joined to the relatively narrower drill pipe or in upper portions of the wellbore where the casing increases in diameter.
U.S. Patent No. 4,361,193 describes a method for mitigating the differential pressure sticking of the drill string and for improving cuttings removal during deviated, rotary drilling. In this technique, the drill cuttings which accumulate on the lower side of the wellbore are swept into the main return stream of the drilling mud flow by the use of radial jets of fluid which are :l~S~4~
projected outwards from the lower portion of the drill string.
These jets impart a stirring movement to the cuttings which settle on the low side of the wellbore and facilitate their removal by the mud which is flowing axially along the annulus. This technique mitigates the problems of differential pressure sticking and cuttings removal to a substantial extent but, because the radial fluid jets are provided in the enlarged portion of the drill string, it does not wholly solve the problems arising from the reduction in mud velocity at the points where the width of the annulus increases.
U. S. Patent No. 4,368,787 discloses a device for reducing the pressure differential sticking of the drill string and for providing improved removal of drill cuttings by using reverse circulation of the drilling mud. The drill bit used in this technique has an internal mud pump which is driven by the bit cones and this pump is used to pump the mud from the annulus, around and through the bit and up the drill pipe in a direction opposite to the normal one. Although this device will obviously mitigate the problems of differential pressure sticking, since there are no drill cuttings in the annulus, it is not entirely free -From this problem because the solid components of the drilling mud are still present and may, in certain circumstances, create a differential sticking problem. In addition, the device would be expensive to fabricate and maintain in normal use because the mud pump components would be subject to a severe degree of abrasion in use from the drill cuttings passing through it.
It would therefore be desirable to have a technique for alieviating the problems described above which did not require the use of complicated downhole apparatus.
The present inventor has now devised a technique for mitigating the problems of cuttings removal and differential pressure sticking in drill strings used in the rotary drilling method. Also, the technique mitigates the problem of cuttings removal between the drill string and casing/liner where the casing 3LZS~ 6 diameter increases. In addition, the technique mitigates the additional problem of "packoff" in the annulus when the drill string is to be withdrawn from the wellbore. The technique is particularly applicable to directional drilling operations, especially in highly deviated boreholes but it is by no means limited to such use. It may be used, if necessary, in conventional, vertically-drilled boreholes if conditions should make it necessary or desirable to do so .
It has been found that if the drilling mud which is passing down the drill string is projected outwards through flow passages in the lower portion of the drill string to form upwardly directed jets, the removal of the drill cuttings will be facilitated and the problems described above substantially mitigated. The upwardly directed jets may suitably be provided by appropriately directed flow passages or nozzles in the drill collars, heavy weight pipe joints or in other, special tool joints in the drill string, where required.
According to the present invention, the method of rotary drilling a borehole, particularly a deviated borehole, into the earth uses a drill string through which the drilling fluid is circulated, a portion of the drilling fluid being passed through flow passages in various portions of the drill string to form jets of drilling fluid having a component of velocity which is directed axially along the borehole in a direction away from the drill bit.
Generally, this will be in an upward direction but in highly deviated holes it will be more "backward" than "upward", although similar considerations will still apply.
The apparatus for drilling by this technique comprises a drilling tool for insertion into the drill string, generally into the lower portion of the string in the proximity of the drill bit or at any location where there is an increase in the radial width of the annulus defined by the outside of the drill string and the walls of the borehole or the casing, this tool being characterized by a number of fluid flow passages which extend from a central, axial \
`` 1.~2~3~'~6 : - 6 ~
passageway in the tool (provided for circulati~n of the drilling mud to the bit) to the exterior of the tool for creating jets of drilling fluid having a component of velocity directed axially along the borehole away from the drill bit, as described above. The drilling tool may be generally in the form of a drilling collar, a joint of heavy weight pipe or it may be incorporated into a specialized tool joint used to connect one section of the drill string to another. The drilling tool is preferably located on the angular shoulder of a lower tool joint, at the point where the width of the annulus increases, so that the axially directed jets of drilling mud help to provide additional fluid volumes and maintain the linear ~luid velocities in this region.
The present invention, then, in one aspect, resides in a method of effecting removal of cuttings resulting fram drilling a borehole into the earth by rotary drilling, which comprises using a drill string comprising serially connected sections of drill pipe through which drilling fluid is circu-lated and at the end of which is a drill bit, in which a portion of the drilling fluid is passed through apertures in at least one portion of the drill string to form ~ets of drilling fluid having a camponent of velocity which is directed axially along the borehole and in a direction away fram the drill bit, and wherein the apertures are provided in the drill string in regions where the radial width of the annulus defined by the outside of the drill string and the walls of the borehole or casing increases.
In another aspect, this invention resides in an apparatus for effecting removal of cuttings resulting from drilling into the earth b~y rotary drilling using a drill camprising serially connected sections of drill pipe through which drilling fluid is circulated and at the end of which is a drill bit, camprising:
(1) a tool for insertion into portions of the drill string, B
~ 2S;~ 6 - 6(a) -
(2) the tool having a central axial passageway for the flow of drilling fluid through the drill string, and
(3) flow passages for drilling 1uid which extend rom the central passageway to the exterior of the tool for creating jets of drilling fluid having a ccmponent o velocity which is directed axially along the ~orehole and in a direction away frcm the bit, the flow passages being situated in a portion of the tool where the annulus defined by the outside o the drill string and the walls of the borehole or casing increases.
In the accompanying drawings:
Figure la is a simplified representation of the lower portion of a drill string in a deviated borehole, foreshortened in length for purposes of convenience;
Figure lb shows a casing/liner and tool joint location also foreshortened in length for purposes of convenience;
Figure 2 is a fragmentary, sectioned elevation of a tool joint including a nozzle for providing an upward flow of drilling mud;
Figure 3 is a view of the exterior of tool joint of Figure 2 showing the position of the nozzle in the angular, exterior shoulder of the tool joint; and Figure 4 is a section of a tool joint similar to that of Figure 2 but with a modified form of nozzle.
The present invention is intended for use in rotary drilling operations in which a drilling rig at the surface is used to rotate the drill string with its attached bit at the bottom.
Drilling fluid or drilling mud is circulated down through the interior of the drill string until it reaches the bit and then passes out through the drill bit and returns to the surface through the annulus between the drill string and the walls of the borehole or liner/casing. Drill collars and heavy weight drill pipe may be B
~,~S~L16 provided at the bottom of the drill string in Grder to maintain the desired weisht on the bit as well as to keep the drill str m g in tension.
Figure la shows the bottom portion of the drill string in a deviated borehole, with the axial scale greatly foreshortened for convenience. The drill bit 10 of conventional rotary cone type is connected to a drill collar 11 and this in turn, is connected to a section of heavy weight pipe 12. As previously mentioned, drill collars are typically about 12 to 25 cm in outside diameter and in practice, a number of drill collars may be used one above the other;
for convenience in the illustration, only one is shown but the same considerations will apply regardless of the actual number used.
Again, more than one joint of heavy weight drill pipe may be used, if necessary. The length of heavy weight drill pipe is joined to bottom joint 13 of the string of drill pipe which extends further up the hole to the drilling rig at the surface. The drilling mud is passed down the interior of the drill string including the heavy weight drill pipe and the drill collar(s) to the bit at which point, it passes out through the bit, picking up the drill cuttings and then returns to the surface through the annulus formed between the drill string and the walls of the borehole or liner/casing, as indicated in the drawing. The annulus is relatively narrow in the region of the drill collar because this is a relatively large diameter component of the drill string. An increase in the width of the annulus occurs at the point where the drill collar gives way to the heavy weight drill pipe and yet a further increase occurs where the heavy weight drill pipe tool joint gives way to the normal pipe diameter and again if the casing diameter increases. Because the flow rate of the drilling mud is maintained at a relatively constant value, different mud velocities are encountered in the regions of differing annulus width, with the mud velocity being greatest in the region of the drill collar and lowest in the region around the normal sized drill pipe. Thus, decreases in the mud velocity occur in the regions marked A and B in Figure la. Another area where the mud velocity decreases is the place where the diameter of the casing <,~
,~
i3~
is increased, leading to an increase in the radial width of the annulus as marked C in Fiyure lb where liner 14 is joined to casing 15 by means of liner cement 16. Tool joint 17 with nozzles is provided near the upper end of liner 14 to prevent packoff. It is in these regions that the problem of packoff of the annulus occurs when attempts are made to withdraw the drill string from the wellbore. The reason for this is that the decrease in the mud velocity aggravates the tendency of the drill cuttings to settle out of the fluid and therefore drill cuttings tend to accumulate in the regions of relatively lower mud velocity. Thus, when attempts are made to withdraw the drill string from the borehole, the upward movement of the drill collar and heavy weight drill pipe tends to consolidate the accumulated cuttings in this region with the result that a compacted mass of drill cuttings forms which may make further withdrawal difficult.
According to the present invention, flow passages are provided in the lower portion of the drill string where the width of the annulus changes. These passages permit drilling fluid to pass from the interior of the drill string to the annulus in the form of jets which have a velocity component which is directed axially along the borehole in a direction away from the drill bit. The fluid jets act to maintain linear fluid velocities and flow patterns in the mud, especially in the regions where the velocity tends to decrease. They also provide additional fluid volume into the larger portions of the annulus as well as stirring up the cuttings, to help maintain them in suspension. The mud flow passages are preferably formed in the angular shoulder of the lowermost section of heavy weight drill pipe but may, in principle, be provided at other points where a decrease in the diameter of the drill string components occurs, for example, at the top of the drill collar, in a special tool joint or sub made for this purpose, or where the diameters of the casings are increased.
Figure 2 shows a drill pipe tool joint or the upper portion 20 of the lowermost tool joint of the heavy weight drill pipe which 5~ 6 has a lower, relatively thick portion 21 and an upper, relatively narrow portion 22 which are joined by an angular shoulder 23. The thicker portion of this pipe joint may be provided at its lower end with a conventional type pin end of a threaded connector for connection to the next lower pipe joint or drill collar and at its upper end with a conventional type of box end threaded connector for connection to the adjacent section of drill pipe in the drill string. The joint has a central axial passageway 24 which permits flow of the drilling mud. An angled, radial passageway 25 extends from central flow passageway 24 out to the angled shoulder 23 of the tool joint, the central axis of angled passageway 25 forming an angle, a, with the center line of the tool joint. A nozzle unit 26 is inserted into the radial passageway, this nozzle unit including a portion 27 which is inserted into a mating portion of passageway 25, and a portion of reduced diameter 28 which fits into a reduced diameter portion of passageway 25. A sealing ring or gasket 29 is provided between the shoulders of the nozzle unit and the machined body of the tool joint. Nozzle unit 26 is retained by means of externally threaded retaining ring 30 which screws into the threaded, large diameter outer portion of passageway 25 (for clarity, screw threads are not shown).
A mud flow passage is provided through nozzle 26 in order to provide the jets of drilling fluid which agitate the drilling mud and drill cuttings in the region of reduced mud velocity, at the point where the width of the annulus increases. The mud flow passage has an inner, axial portion 31 and an outer, inclined portion 32 which terminates in orifice 33 on the face of nozzle unit 26. The axis of outer portion 32 of the mud flow passage is parallel to the axis of the tool joint so that, in this case, the emerging jets oF drilling mud are directed axially along the borehole in a direction directly away from the drill bit. An axial slot 34 is machined into shoulder 23 of the tool joint in order to permit egress of the fluid in the desired direction. In order to prevent rotation of nozzle unit 26 in passageway 25, a slot may be ~2S3~3~6 machined in the larger diameter portion of the nozzle unit, with a corresponding slot machined in the body of the tool joint so that a key, e.g., a Woodruff key, may be inserted to maintain the desire~
orientation. In case it may be desired to vary the direction in which the emerging fluid jets leave the nozzle unit, a number of keyways may be formed so that the orientation retaining key may be placed into any one of them to maintain the nozzle unit in the appropriate orientation (slot 34 may be enlarged to a "keyhole" type configuration if this is done, so as to permit free flow of the fluids).
In order to supplement the velocity of the drilling mud evenly around the periphery of the shoulder, a plurality of nozzles is preferably provided, arranged at equal intervals around the periphery. Normally, three or four nozzles will be preferred, although fewer may be provided since the rotation of the drill string will cause the emerging fluid jets to agitate the drilling mud completely around the annulus as the drill string rotates.
In the embodiment shown in Figures 2 and 3, the jets of drilling fluid leaving the nozzle unit emerge in a direction which is parallel to the axis of the tool joint. However, this is not necessary provided that the emerging jets of drilling fluid have a velocity component which is directed along the borehole in a direction away from the drill bit. Figure 4 shows a modified form of tool joint which is generally similar to that shown in Figures 2 and 3 (and similar parts are given similar reference numerals for convenience) but in this case nozzle unit 26 has a mud flow passageway 40 which is entirely straight. In this case, the fluid ~ets emerge Ln such a way that they have a rat~ial oom~onent of velocity as well as a component which is axial with respect to the borehole, the axial component being directed in a direction away from the drill bit. In this case, it is the axial component of the velocity which supplements the velocity of mud flow in this region and helps to prevent the packoff problems which are mentioned above. The radial component will, however, help to stir up the cuttings and ,.~J,~ji t S~3f.~6 maintain thern in suspension. Again, a number of nozzle units may be provided around the periphery of the angular shoulder, preferably three or four as stated above although fewer may be found to be sufficient.
The nozzle units may each incorporate a suitable pressure drop-actuated check valve 42, shown schematically in Figure 4, which causes the nozzle to close when the mud flow rates reach a predetermined value and the nozzle action is not required. In addition, it is not essential that the jets should emerge in a direction which has purely axial and radial components, as with the nozzle units shown in Figure 2 to 4, but if desired, the nozzle or nozzles may be set so that the jets emerge in a direction which is partially tangential to the surface of the tool joint. This will tend to produce a helical direction of mud flow in the region above the nozzle. This arrangement will not, however, be generally preferred, mainly because of difficulties in machining the passageways at the appropriate angles. Generally, the diameter of the mud flow passageways will be approximately 5 to 10 mm.
The use of the tool joints described above agitates the drill cuttings so as to help prevent them from settling, as well as providing additional fluid volume in the region where the width of the annulus increases, thereby tending to disperse the drill cuttings in a larger volume of drilling mud; this, in itself, helps to prevent packoff problems when the drill string is withdrawn. In addition, the emerging mud may provide a jetting action on a cuttings bed that is being plowed as the drill string is withdrawn from the borehole, further assisting withdrawal of the drill string.
In the accompanying drawings:
Figure la is a simplified representation of the lower portion of a drill string in a deviated borehole, foreshortened in length for purposes of convenience;
Figure lb shows a casing/liner and tool joint location also foreshortened in length for purposes of convenience;
Figure 2 is a fragmentary, sectioned elevation of a tool joint including a nozzle for providing an upward flow of drilling mud;
Figure 3 is a view of the exterior of tool joint of Figure 2 showing the position of the nozzle in the angular, exterior shoulder of the tool joint; and Figure 4 is a section of a tool joint similar to that of Figure 2 but with a modified form of nozzle.
The present invention is intended for use in rotary drilling operations in which a drilling rig at the surface is used to rotate the drill string with its attached bit at the bottom.
Drilling fluid or drilling mud is circulated down through the interior of the drill string until it reaches the bit and then passes out through the drill bit and returns to the surface through the annulus between the drill string and the walls of the borehole or liner/casing. Drill collars and heavy weight drill pipe may be B
~,~S~L16 provided at the bottom of the drill string in Grder to maintain the desired weisht on the bit as well as to keep the drill str m g in tension.
Figure la shows the bottom portion of the drill string in a deviated borehole, with the axial scale greatly foreshortened for convenience. The drill bit 10 of conventional rotary cone type is connected to a drill collar 11 and this in turn, is connected to a section of heavy weight pipe 12. As previously mentioned, drill collars are typically about 12 to 25 cm in outside diameter and in practice, a number of drill collars may be used one above the other;
for convenience in the illustration, only one is shown but the same considerations will apply regardless of the actual number used.
Again, more than one joint of heavy weight drill pipe may be used, if necessary. The length of heavy weight drill pipe is joined to bottom joint 13 of the string of drill pipe which extends further up the hole to the drilling rig at the surface. The drilling mud is passed down the interior of the drill string including the heavy weight drill pipe and the drill collar(s) to the bit at which point, it passes out through the bit, picking up the drill cuttings and then returns to the surface through the annulus formed between the drill string and the walls of the borehole or liner/casing, as indicated in the drawing. The annulus is relatively narrow in the region of the drill collar because this is a relatively large diameter component of the drill string. An increase in the width of the annulus occurs at the point where the drill collar gives way to the heavy weight drill pipe and yet a further increase occurs where the heavy weight drill pipe tool joint gives way to the normal pipe diameter and again if the casing diameter increases. Because the flow rate of the drilling mud is maintained at a relatively constant value, different mud velocities are encountered in the regions of differing annulus width, with the mud velocity being greatest in the region of the drill collar and lowest in the region around the normal sized drill pipe. Thus, decreases in the mud velocity occur in the regions marked A and B in Figure la. Another area where the mud velocity decreases is the place where the diameter of the casing <,~
,~
i3~
is increased, leading to an increase in the radial width of the annulus as marked C in Fiyure lb where liner 14 is joined to casing 15 by means of liner cement 16. Tool joint 17 with nozzles is provided near the upper end of liner 14 to prevent packoff. It is in these regions that the problem of packoff of the annulus occurs when attempts are made to withdraw the drill string from the wellbore. The reason for this is that the decrease in the mud velocity aggravates the tendency of the drill cuttings to settle out of the fluid and therefore drill cuttings tend to accumulate in the regions of relatively lower mud velocity. Thus, when attempts are made to withdraw the drill string from the borehole, the upward movement of the drill collar and heavy weight drill pipe tends to consolidate the accumulated cuttings in this region with the result that a compacted mass of drill cuttings forms which may make further withdrawal difficult.
According to the present invention, flow passages are provided in the lower portion of the drill string where the width of the annulus changes. These passages permit drilling fluid to pass from the interior of the drill string to the annulus in the form of jets which have a velocity component which is directed axially along the borehole in a direction away from the drill bit. The fluid jets act to maintain linear fluid velocities and flow patterns in the mud, especially in the regions where the velocity tends to decrease. They also provide additional fluid volume into the larger portions of the annulus as well as stirring up the cuttings, to help maintain them in suspension. The mud flow passages are preferably formed in the angular shoulder of the lowermost section of heavy weight drill pipe but may, in principle, be provided at other points where a decrease in the diameter of the drill string components occurs, for example, at the top of the drill collar, in a special tool joint or sub made for this purpose, or where the diameters of the casings are increased.
Figure 2 shows a drill pipe tool joint or the upper portion 20 of the lowermost tool joint of the heavy weight drill pipe which 5~ 6 has a lower, relatively thick portion 21 and an upper, relatively narrow portion 22 which are joined by an angular shoulder 23. The thicker portion of this pipe joint may be provided at its lower end with a conventional type pin end of a threaded connector for connection to the next lower pipe joint or drill collar and at its upper end with a conventional type of box end threaded connector for connection to the adjacent section of drill pipe in the drill string. The joint has a central axial passageway 24 which permits flow of the drilling mud. An angled, radial passageway 25 extends from central flow passageway 24 out to the angled shoulder 23 of the tool joint, the central axis of angled passageway 25 forming an angle, a, with the center line of the tool joint. A nozzle unit 26 is inserted into the radial passageway, this nozzle unit including a portion 27 which is inserted into a mating portion of passageway 25, and a portion of reduced diameter 28 which fits into a reduced diameter portion of passageway 25. A sealing ring or gasket 29 is provided between the shoulders of the nozzle unit and the machined body of the tool joint. Nozzle unit 26 is retained by means of externally threaded retaining ring 30 which screws into the threaded, large diameter outer portion of passageway 25 (for clarity, screw threads are not shown).
A mud flow passage is provided through nozzle 26 in order to provide the jets of drilling fluid which agitate the drilling mud and drill cuttings in the region of reduced mud velocity, at the point where the width of the annulus increases. The mud flow passage has an inner, axial portion 31 and an outer, inclined portion 32 which terminates in orifice 33 on the face of nozzle unit 26. The axis of outer portion 32 of the mud flow passage is parallel to the axis of the tool joint so that, in this case, the emerging jets oF drilling mud are directed axially along the borehole in a direction directly away from the drill bit. An axial slot 34 is machined into shoulder 23 of the tool joint in order to permit egress of the fluid in the desired direction. In order to prevent rotation of nozzle unit 26 in passageway 25, a slot may be ~2S3~3~6 machined in the larger diameter portion of the nozzle unit, with a corresponding slot machined in the body of the tool joint so that a key, e.g., a Woodruff key, may be inserted to maintain the desire~
orientation. In case it may be desired to vary the direction in which the emerging fluid jets leave the nozzle unit, a number of keyways may be formed so that the orientation retaining key may be placed into any one of them to maintain the nozzle unit in the appropriate orientation (slot 34 may be enlarged to a "keyhole" type configuration if this is done, so as to permit free flow of the fluids).
In order to supplement the velocity of the drilling mud evenly around the periphery of the shoulder, a plurality of nozzles is preferably provided, arranged at equal intervals around the periphery. Normally, three or four nozzles will be preferred, although fewer may be provided since the rotation of the drill string will cause the emerging fluid jets to agitate the drilling mud completely around the annulus as the drill string rotates.
In the embodiment shown in Figures 2 and 3, the jets of drilling fluid leaving the nozzle unit emerge in a direction which is parallel to the axis of the tool joint. However, this is not necessary provided that the emerging jets of drilling fluid have a velocity component which is directed along the borehole in a direction away from the drill bit. Figure 4 shows a modified form of tool joint which is generally similar to that shown in Figures 2 and 3 (and similar parts are given similar reference numerals for convenience) but in this case nozzle unit 26 has a mud flow passageway 40 which is entirely straight. In this case, the fluid ~ets emerge Ln such a way that they have a rat~ial oom~onent of velocity as well as a component which is axial with respect to the borehole, the axial component being directed in a direction away from the drill bit. In this case, it is the axial component of the velocity which supplements the velocity of mud flow in this region and helps to prevent the packoff problems which are mentioned above. The radial component will, however, help to stir up the cuttings and ,.~J,~ji t S~3f.~6 maintain thern in suspension. Again, a number of nozzle units may be provided around the periphery of the angular shoulder, preferably three or four as stated above although fewer may be found to be sufficient.
The nozzle units may each incorporate a suitable pressure drop-actuated check valve 42, shown schematically in Figure 4, which causes the nozzle to close when the mud flow rates reach a predetermined value and the nozzle action is not required. In addition, it is not essential that the jets should emerge in a direction which has purely axial and radial components, as with the nozzle units shown in Figure 2 to 4, but if desired, the nozzle or nozzles may be set so that the jets emerge in a direction which is partially tangential to the surface of the tool joint. This will tend to produce a helical direction of mud flow in the region above the nozzle. This arrangement will not, however, be generally preferred, mainly because of difficulties in machining the passageways at the appropriate angles. Generally, the diameter of the mud flow passageways will be approximately 5 to 10 mm.
The use of the tool joints described above agitates the drill cuttings so as to help prevent them from settling, as well as providing additional fluid volume in the region where the width of the annulus increases, thereby tending to disperse the drill cuttings in a larger volume of drilling mud; this, in itself, helps to prevent packoff problems when the drill string is withdrawn. In addition, the emerging mud may provide a jetting action on a cuttings bed that is being plowed as the drill string is withdrawn from the borehole, further assisting withdrawal of the drill string.
Claims (10)
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of effecting removal of cuttings resulting from drilling a borehole into the earth by rotary drilling, which comprises using a drill string comprising serially connected sections of drill pipe through which drilling fluid is circulated and at the end of which is a drill bit, in which a portion of the drilling fluid is passed through apertures in at least one portion of the drill string to form jets of drilling fluid having a component of velocity which is directed axially along the borehole and in a direction away from the drill bit, and wherein the apertures are provided in the drill string in regions where the radial width of the annulus defined by the outside of the drill string and the walls of the borehole or casing increases.
2. A method according to claim 1 in which the borehole is a deviated borehole.
3. A method according to claim 1 in which the jets of drilling fluid emerge from the apertures in a direction which is axially along the borehole away from the drill bit.
4. A method according to claim 1 in which the jets of drilling fluid emerge from the apertures in a direction having a component of velocity which is radial with respect to the borehole and a component of velocity which is axial with respect to the borehole and is directed axially along the borehole in a direction away from the drill bit.
5. A method according to claim 1 in which the drilling fluid passes through a plurality of apertures in the lower portion of the drill string.
6. Apparatus for effecting removal of cuttings resulting from drilling into the earth by rotary drilling using a drill comprising serially connected sections of drill pipe through which drilling fluid is circulated and at the end of which is a drill bit, comprising:
(1) a tool for insertion into portions of the drill string, (2) the tool having a central axial passageway for the flow of drilling fluid through the drill string, and (3) flow passages for drilling fluid which extend from the central passageway to the exterior of the tool for creating jets of drilling fluid having a component of velocity which is directed axially alng the borehole and in adirection away from the bit, the flow passages being situated in a portion of the tool where the annulus defined by the outside of the drill string and the walls of the borehole or casing increases.
(1) a tool for insertion into portions of the drill string, (2) the tool having a central axial passageway for the flow of drilling fluid through the drill string, and (3) flow passages for drilling fluid which extend from the central passageway to the exterior of the tool for creating jets of drilling fluid having a component of velocity which is directed axially alng the borehole and in adirection away from the bit, the flow passages being situated in a portion of the tool where the annulus defined by the outside of the drill string and the walls of the borehole or casing increases.
7. Apparatus according to claim 6 which includes a plurality of the fluid flaw passages arranged peripherally around the tool at one axial position along its length.
8. Apparatus according to claim 7 in which the plurality of fluid flow passages are provided in an angular shoulder of the tool at a point where its external diameter changes.
9. Apparatus according to claim 6 in which the fluid flow passages are adapted to direct the jets of fluid axially along the borehole in a direction away from the drill bit.
10. Apparatus according to claim 6 in which the fluid flow passages are adapted to direct the jets of drilling fluid such that they have a velocity component which is radial to the borehole and a component which is directed axially along the borehole and in a direction away from the drill bit.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US68103184A | 1984-12-12 | 1984-12-12 | |
| US681,031 | 1984-12-12 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1253846A true CA1253846A (en) | 1989-05-09 |
Family
ID=24733512
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000496078A Expired CA1253846A (en) | 1984-12-12 | 1985-11-25 | Method for improving cuttings removal in drilling deviated wellbores |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1253846A (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5861362A (en) * | 1992-01-06 | 1999-01-19 | Blue Diamond Growers | Almond shell additive and method of inhibiting sticking in wells |
| US9291019B2 (en) | 2011-12-20 | 2016-03-22 | Exxonmobil Upstream Research Company | Systems and methods to inhibit packoff formation during drilling assembly removal from a wellbore |
| CN109653691A (en) * | 2019-02-27 | 2019-04-19 | 西南石油大学 | A kind of waterpower and mechanical composite controllable cutting bed cleanout tool |
| CN111894496A (en) * | 2020-03-16 | 2020-11-06 | 重庆科技学院 | Drilling pressure control type underground circulation short circuit and coiled tubing drill plug dynamic flushing process |
-
1985
- 1985-11-25 CA CA000496078A patent/CA1253846A/en not_active Expired
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5861362A (en) * | 1992-01-06 | 1999-01-19 | Blue Diamond Growers | Almond shell additive and method of inhibiting sticking in wells |
| US9291019B2 (en) | 2011-12-20 | 2016-03-22 | Exxonmobil Upstream Research Company | Systems and methods to inhibit packoff formation during drilling assembly removal from a wellbore |
| US9291018B2 (en) | 2011-12-20 | 2016-03-22 | Exxonmobil Upstream Research Company | Systems and methods to inhibit packoff events during downhole assembly motion within a wellbore |
| CN109653691A (en) * | 2019-02-27 | 2019-04-19 | 西南石油大学 | A kind of waterpower and mechanical composite controllable cutting bed cleanout tool |
| CN109653691B (en) * | 2019-02-27 | 2024-01-26 | 西南石油大学 | Hydraulic and mechanical compound controllable rock debris bed cleaning tool |
| CN111894496A (en) * | 2020-03-16 | 2020-11-06 | 重庆科技学院 | Drilling pressure control type underground circulation short circuit and coiled tubing drill plug dynamic flushing process |
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