CA2366134A1 - Underreamer - Google Patents

Description

UNDERREAMER
Summary of the invention When drilling a borehole through an earthen formation a pilot hole is drilled by a pilot bit and the hole can be enlarged by a underreamer. Underreamers have arms with cutters thereon that cut into the formation to enlarge the borehole to its intended guage.
An under reamer has been invented having at least one lower underreamer arm and at least one upper underreamer arm. The lower arm is designated as the one closest to the lower end of the tool, which is the end that will be positioned closest to the pilot bit and the upper underreamer arm is positioned further than the lower underreamer arm from the lower end of the underreamer and, in other words, closer to surface when the tool is positioned in the borehole.
Underreamers are useful in casing drilling, wherein the pilot bit drills the pilot hole into the formation and underreamers enlarge the hole to permit advancement of the casing.
Underreamers are also useful when extending a borehole below installed casing.
In such embodiments, the arms are collapsible to permit the underreamer to be moved through the bore of the casing and are expandable downhole to permit drilling of a borehole to a guage greater than the outer diameter of the casing. Thus, one embodiment there is provided an underreamer comprising a housing including an upper end and a lower end, the lower end being connectable to a pilot bit-containing assembly; an upper underreamer arm carried by the housing and being moveable between an expanded position extending out from the housing to define an upper expanded diameter and a retracted position, wherein the upper arms define an upper arm retracted diameter less than the upper expanded diameter; a lower underreamer arm carried by the housing and being moveable between an expanded position extending out from the housing and defining a lower expanded diameter and a retracted position, wherein the arms define a lower arm retracted diameter which is less than the expanded effective diameter, the lower underreamer arm being positioned between the upper underreamer arm and the lower end of the housing; an actuator for driving the upper underreamer arm between the retracted position and S:\04\472\32361\122\0001-2-app.doc the expanded position; and an actuator for driving the lower underreamer arm between the retracted position and the expanded position.
The actuator for driving the upper underreamer arm and the actuator for driving the lower underreamer arm can be the same or separate mechanisms. They can be any desired mechanism including a fluid pressure or spring biased arrangement which acts against an inner surface of the arm, an arrangement of a pivotal connection on the arm and a drive rack and pinion mechanism or a cam mechanism.
There can be one or more lower arms and one or more upper arms. For example, there can be a plurality of lower arms spaced about the housing positioned substantially in a common plane. As another example, there can be a plurality of upper arms spaced about the housing positioned substantially in a plane.
In addition to the upper anm and the lower arm, there can be further intermediate arms positioned between the upper arm and the lower arm. Where the underreamer must be sized to move through the casing inner bore, the intermediate arms should be retractable.
The upper and lower arms when in their retracted positions can be in various configurations such as, for example, recessed into slots, indentations, etc. in the housing or folded against the housing. The retracted diameters of the upper arm and the lower arm can be the same or different, but each is less than the minimum drift diameter for the particular application in which the underreamer is to be used, such as the drift diameter for casing string used in a drilling operation.
The upper and lower arms can be axially aligned along the housing or offset from each other.
The expanded diameters of the upper arm and the lower arm can be the same or different, as desired. In one embodiment, the lower arm expanded diameter is less than the upper arm expanded diameter. In another embodiment, the lower arm expanded diameter is substantially equal to the upper arm expanded diameter. It will be appreciated that the actual expanded S:~C4W72~323611122\0001-2-app.doc diameter of an underreamer arm can change with time due to wear on the cutting surface or in the connection to the housing. However, reference to the expanded diameter in the application is intended in reference to a underreamer wherein no wear has occurred.
The upper underreamer arm and the lower underreamer arm can vary in function.
In particular, the lower underreamer arm generally performs the primary hole enlarging function and, therefore, includes cutters suitable for drilling into the formation, such as those containing diamonds, as for example polycrystalline diamond compact (PDC) material, to enlarge the pilot hole to the expanded diameter of lower arm.
The upper underreamer arm can also include cutters suitable for drilling into the formation. In such an embodiment, the upper underreamer arm can have an expanded diameter substantially similar to the lower arm expanded diameter, or, alternately, the upper arm expanded diameter can be greater than the lower arm expanded diameter and the upper arm acts to further enlarge the borehole to a desired guage.
In another embodiment, the upper underreamer arm does not include cutters and can act to clean the hole, stabilize the drill string behind the lower underreamer arm and/or provide an indication that the borehole is under guage, for example due to wear of the lower underreamer arm, as determined by an increase in torque on the drilling assembly. To enhance the use of the upper underreamer arm, surface hardening can be used at least on the surface that can come into contact with the formation. Surface hardening includes hard facing or application of fine or coarse abrasion resistant materials such as tungsten/carbide coatings. It will be appreciated that while surface hardened components can be used to cut into a formation in a limited way, such components would not be useful for drilling into a formation. Surface hardening can be used alone or in addition to cutters.
Brief Description of the Drawings Figure 1 is a schematic sectional view through a portion of a borehole and disposed therein a drill string for use in drilling with casing.
S:\C4\472132361\122\OOOI-2-app.doc Figure 2 is schematic view of another underreamer.
Figure 3 is an isometric view of another underreamer.
Figure 4 is a quarter section, isometric view of the underreamer of Figure 3.
Figure 5 is a section along line V-V of Figure 3.
Figure 6 is a section as in Figure 5 with the underreamer arms in the retracted position.
Figure 7 is a section along line B-B of Figure 6.
Figure 8 is an isometric view of an underreamer arm useful in an underreamer.
Detailed Description of the Invention Referring to Figure l, a schematic section through a borehole is shown. The borehole is extended by a drilling assembly disposed therein. The drilling assembly is engaged at the lower end of a string of casing, which is acting as the drill string. The drilling assembly includes a lock housing including lock means (not shown) for releasably securing the drilling assembly to the casing string, a pilot bit, which is drilling a pilot hole and an underreamer disposed therebetween.
A drilling assembly can alternately include many other components, such as bent subs, MWD
devices, etc. However, those devices are not included in the illustrated assembly for simplicity.
The drilling assembly is rotated either by rotation of the casing string from surface, as would be the case in the illustrated embodiment, or by inclusion of a mud motor in the drilling assembly.
The underreamer includes a housing and is connected into the drilling assembly through an upper end and a lower end. The lower end is positioned adjacent the pilot bit. The underreamer includes a pair of upper underreamer arms and a pair of lower underreamer arms. While in the S:\C44472~32361\122\0001-2-app.doc 4, illustrated embodiment each of the sets of upper and; lower underreamer arms includes a pair of arms, it is to be understood that other numbers, for example, one or more arms can be used in each position.
The lower pair of arms and the upper pair of arms spaced longitudinally along the housing and, in particular, the lower underreamer arms are positioned adjacent the lower end of the underreamer and between the lower end and the upper arms. In the expanded position, as shown, the lower arms act to enlarge the pilot hole to borehole guage. The expanded diameter of the upper arms Du is substantially equal to the expanded diameter Dl of the lower arms. The upper arms in the illustrated embodiment include cutters thereon and when expanded, as shown, clean out the hole behind the lower arms, provide a stabilization effect close to the primary hole enlarging underreamer arms and act as a backup to the lower underreamer arms should they begin to wear and drill under guage. The upper. arms also may provide an indication that the lower arms are operating under guage by observing the drill string torque at surface.
The upper arms and the lower arms are axially aligned along the housing. When it is desired to pull the drilling assembly uphole for repair or replacement of any of the components or in preparation for completion of the borehole, the underreamer arms can be retracted against the housing to permit the drilling assembly to fit through the casing inner bore.
An actuator, cannot be seen, within the housing is operated to move the underreamer arms between their expanded positions and their retracted positions. The actuator can take various forms, but is preferably actuated remotely such as, for example, by a change in fluid pressure, an acoustic pulse or by engagement against the casing shoe.
Referring to Figure 2, an underreamer is shown in a schematic form having a housing, an upper end, a lower end, and four pairs of underreamer arms (all shown in their expanded position). The underreamer arms include, from the lower most arms to the upper most arms, a lower pair of cutting arms, a lower pair of stabilizer arms, an upper pair of cutter arms and an upper pair of stabilizer arms. Each pair of underreamer arms operates in a single plane and the plane of each of the pairs is spaced longitudinally along the underreamer from the planes of its adjacent pairs.
S:\C4\472U2361\122\0001-2-app.doc Each of the cutting arms includes cutters selected to drill through the formation being penetrated by the borehole. The cutters can be, for example, formed of PDC. Each of the stabilizing arms are coated at their outer end with hard facing formed of a matrix containing carbide/tungsten particles. This coating prevents erosion and hardens the surface to decrease the rate of material degradation by engagement against the rock of the formation.
Lower cutting arms, when expanded, define a diameter Dlca, to which a pilot hole would be enlarged, when the lower cutting arms are drilled therethrough. The upper cutting arms are formed to have a diameter Duca, when expanded, that is greater than diameter Dlca. Thus, when the illustrated underreamer is operated behind a pilot bit, the hole will be enlarged to a diameter Dlca and then increased to the diameter Duca by the upper cutting arms. Duca is generally the selected final guage for the borehole. Thus the hole will be enlarged in two stages and the operation will be divided between two sets of cutters. This can extend the useful life of the underreamer cutters, can result in torque reduction and can ease steering in a directional drilling operation.
The lower stabilizing arms are formed to have substantially the same expanded diameter as diameter Dlca and the upper stabilizer arms have an extended diameter substantially equal to Duca. As such, the stabilizer arms do not operate to enlarge the hole behind their respective cutting arms, but bear at their guage contact face against the borehole wall to stabilize the underreamer adjacent the cutting arms.
Refernng to Figures 3 to 7, there is shown another underreamer. Some underreamer arms are illustrated in Figures 8 that are useful in the underreamer of Figures 3 to 7.
The underreamer includes a housing having an outer surface, an inner bore, a threaded lower end for connection directly or indirectly to a pilot bit and a threaded upper end for connection directly or indirectly to the lock housing or to a drill string A pilot bit stabilizer is formed on the outer surface of the housing adjacent its lower end.
S:\C4\472132361\122\0001-2-app.doc The housing supports a plurality of underreamer arms including three lower cutting arms and three upper stabilizer arms. The underreamer arms are pivotally ~ connected in slots in the housing by pivot pins secured in holes by bolts. The slots for the upper underreamer arms are spaced about the circumference of the housing and the slots for the lower underreamer arms are spaced about the circumference of the housing. The lower underreamer arm slots are spaced along the long axis and radially offset from the slots for the upper underreamer arms such that the lower arms are positioned below and are oriented between the upper arms.
The arms are each actuated to move between an expanded position, shown in Figures 3 and 4, and a retracted position, shown in Figures 5 and 6. The actuator includes a mandrel slid ably disposed in the inner bore of the housing. The mandrel includes a plurality of rack gears, which each mesh with a pinion gear formed on the rear surface of one of the arms. As will be appreciated, longitudinal movement of the mandrel within the inner bore will drive the arms to rotate about their pivot pins, in unison. The mandrel is prevented from rotating about its long axis within the bore by a pin that engages in an elongate keyway. The pin and the keyway are correspondingly sized such that the mandrel can slide a selected distance within the bore but cannot rotate therein.
The mandrel is normally biased into a position that maintains the arms in a retracted position in their slots. Biasing is provided by a spring acting between a shoulder on the mandrel and a shoulder on the inner bore of the housing. The spring is positioned in a spring chamber with ports that provide communication with the ambient pressure about the underreamer.
The mandrel is driven to move within the bore by increasing the fluid pressure in the inner bore of the housing. In particular, mandrel includes a piston face against which fluid pressure can act to compress the spring. When moved in this way, the rack gears are driven relative to the arm pinion gears to rotate the arms about their pivot pins. The mandrel includes a bore for passage of drilling fluid to the pilot bit. Seals are disposed between the mandrel and the inner bore to seal against passage of drilling fluid therebetween. If desired, fluid jet ports can be provided adjacent the arms to provide for cleaning of the slots. A choke jet can be provided to regulate fluid flow to the pilot bit and to provide a greater fluid pressure thereabove, about the mandrel.
S:\04\472112361\122\0001-2-app.doc The slots are sized relative to the arms to permit each arm to be retracted such that its upper surface is generally flush with the outer surface of the housing. The slots also preferably provide support for the arms when they are in the expanded position and in operation.
In particular, the arms and slots are generally correspondingly shaped about their tops and sides. The edges of the slots can be built up, as desired, to increase the area of the support surface.
Underreamer arms that are useful in the present invention can take various forms. In one embodiment, the arms include a rear pinion gear and an opening for insertion therethrough of the pivot pin. The distance from the connection point to the housing, in this case the pivot pin opening, to the guage contact face will affect the expanded diameter of the underreamer arm.
Thus, it will be appreciated that an upper arm can have a greater distance from the pivot pin opening to the guage contact face.
In one embodiment, a shoulder is formed on the underreamer arm that acts to increase the thickness of the arm at its outer end. Thus, although a smaller thickness can be used at the connection end, the cutting or stabilizing face of the arm can be increased.
Preferably, the shoulder is positioned along the arm so that it corresponds with the outer edge of the slot in which the arm is mounted. This provides that the shoulder can seat against the outer edge of the slot and transfer a portion of the force applied to the arm to the housing at this point. This takes some of the stress off of the pivot pin.
S:\C4\472\323b I \I 22\0001-2-app.doc

Claims