Force Stacking Assembly for Use with a Subterranean Excavating System

A force stacking assembly for use with an earth boring system that includes a series of actuators that each generate a force, and that are arranged to create a combined force that is cumulative of all of the actuators. The actuators include members that react in response to an applied stimulus, such as from an electrical current or magnetic field. The members are arranged in series in a hollow housing, planar bulkheads are transversely mounted in the housing. Each of the members have an end axially abutting a corresponding bulkhead. Ends of each member distal from it corresponding bulkhead couple to a ram member, that in turn couples to a drill bit. Energizing the members causes each to exert a force against the ram member, which is transferred to the bit.

BACKGROUND

1. Field of the Disclosure

The present disclosure relates to a system for use with a borehole excavating system that employs reactive materials that selectively generate impulse forces in the excavating system.

2. Description of Prior Art

Hydrocarbon producing wellbores extend below the Earth's surface where they intersect subterranean formations in which hydrocarbons are trapped. The wellbores generally are created by drill bits that are on the end of a drill string, where typically a drive system above the opening to the wellbore rotates the drill string and bit. Cutting elements on the drill bit scrape or otherwise impact the bottom of the wellbore as the bit is rotated and excavate material from the formation thereby deepening the wellbore. Drilling fluid is typically pumped down the drill string and discharged from the drill bit into the wellbore. The drilling fluid flows back up the wellbore in an annulus between the drill string and walls of the wellbore. Cuttings produced while excavating are carried up the wellbore with the circulating drilling fluid.

During drilling, cutters or teeth formed on the cutting surfaces of the drilling bits impart forces onto the subterranean formation. The forces include shear forces generated by rotation of the drill bit with respect to the bottom of the borehole. Compressional forces are also transferred between the bit and formation, where the compressional forces are from a combination of the weight of a drill string on which the bit is attached and a column of drilling fluid flowing within an axial bore in the drill string. Except when changing bits due to wear or failure, the bit remains in contact with the formation during drilling of the wellbore.

SUMMARY

Disclosed herein is an example of a system for excavating within a wellbore and that includes a drill string, a housing having an end that couples to the drill string, actuators in the housing that are selectively extendable and that each have an end coupled with the housing, and a ram assembly having an end coupled to a drill bit, and that couples to ends of the actuators opposite from the ends of the actuators that couple with the housing, so that when the actuators are selectively extended, the drill bit selectively extends a distance from the drill string.

In an example, each of the actuators exerts a force onto the ram assembly when selectively extended, and wherein the actuators are arranged in series in the housing such that a sum of the forces is transmitted to the ram assembly. In an example when the actuators are selectively extended, the drill bit is axially displaced an amount substantially equal to the axial elongation of a one of the actuators. The members can optionally be made from an activatable material that elongates in response to applied electricity. Examples of activatable material include piezoelectric material, a magnetorestrictive material, and combinations thereof.

In one embodiment, the bit is made up of an outer bit having an axial bore, and an inner bit that reciprocates within the axial bore in response to the actuators being changed into the activated state. The actuators can be axially elongated when selectively activated. Optionally, the housing can hollow with bulkheads formed in the housing at axially spaced apart locations, and wherein outer peripheries of each of the bulkheads couple with an inner surface of sidewalls of the housing. In this example, the ends of the actuators that couple with the housing are in abutting contact with the bulkheads. In an embodiment, planar radial walls are provided inside of ram assembly, and that extend in a direction transverse to an axis of the ram assembly, and wherein ends of the actuators that couple with the ram assembly abut the radial walls. In an alternative, the ram member coaxially moves within the housing when the actuators are selectively extended.

Also disclosed herein is a method of excavating within a wellbore and that includes rotating a drill string in the wellbore that includes drill pipe, a drill bit coupled to the drill pipe, and actuators disposed between the drill pipe and drill bit, generating actuating forces with the actuators by selectively elongating each of the actuators a designated distance, and imparting a summation of the actuating forces against the drill bit to urge at least a portion of the drill bit away from the drill pipe an urged distance that is substantially the same as the designated distance.

The actuators can be elongated at a resonant frequency, such as a resonant frequency of the drill string, or a resonant frequency of a formation that surrounds the wellbore. Selectively elongating each of the actuators a designated distance can involve directing electricity to a magnetorestrictive member disposed in the actuator that axially expands and generates a one of the axial forces. The portion of the drill bit urged away from the drill pipe can be an inner bit that is proximate an axis of the drill bit. In one embodiment, at least a portion of the drill bit is all of the drill bit, and when at least a portion of the drill bit is urged away from the drill pipe the urged distance, the drill bit is urged into excavating contact with a bottom of the wellbore.

Another example of a system for excavating within a wellbore is described herein and that includes a bottom hole assembly that selectively couples to a drill string, actuators in the bottom hole assembly that are selectively extendable a designated distance and that each exert a force when extended, a drill bit coupled with the bottom hole assembly, and a means for transferring the combined forces exerted by the actuators to the drill bit, and urging the drill bit a distance away from the drill string that is substantially the same as the designated distance. The actuators can include members made up of material that is responsive to an application of electricity. The bottom hole assembly can further include a housing that is coupled with the drill string, and wherein members are arranged in series in the housing, and ends of each of the members are coupled with the housing. In one alternate embodiment, the bottom hole assembly includes a ram assembly that couples to the drill bit, and wherein ends of the members opposite from the ends that couple with the housing couple to the ram assembly, so that when the members expand, the ram assembly is urged axially a distance that is substantially the same.

Embodiments described here are not intended to limit the present disclosure to those embodiments. On the contrary, the present disclosure is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of what is described.

DETAILED DESCRIPTION

The method and system of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The method and system of the present disclosure may be in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey its scope to those skilled in the art. Like numbers refer to like elements throughout. In an embodiment, usage of the term “about” includes +/−5% of the cited magnitude. In an embodiment, usage of the term “substantially” includes +/−5% of the cited magnitude.

Shown in a side sectional view inFIG. 1is one example of a drilling system10for use in forming a wellbore12. In this example wellbore12intersects formation14, and a wellbore wall15is defined at the intersection of wellbore12and formation14. A drill string16is shown projecting into wellbore12and which is rotated by a rotary table18on surface. Sections of drill pipe20may be added on top of drill string16with use of a derrick22shown mounted over an opening of wellbore12. Optionally, a top drive (not shown) may be mounted to derrick22and used for rotating drill string16in lieu of rotary table18. A bottom hole assembly (“BHA”)24is shown coupled to drill string16. BHA24is made up of an elongated housing26that is hollow and whose outer periphery is made up of sidewalls27that extend along a length of the housing26and curve around an axis AXof BHA24. The outer surface of sidewalls27resembles a cylindrical shape. Inside of housing26are elongate compartments281-nthat are formed in series. The compartments281-nare defined between planar bulkheads301-nthat project radially between the sidewalls27of housing26at axially spaced apart locations. A ram assembly32is shown coaxially disposed within housing26, and which has sidewalls33that define an outer lateral periphery of the ram assembly32. Sidewalls33of the ram assembly32are curved around the axis AXof the bottom hole assembly24and extend generally parallel with sidewalls27of housing26. Similar to the bulkheads301-nin housing26, are planar radial walls341,342that extend radially between the sidewalls of the ram assembly32at axially spaced apart locations to form compartments361-nwithin ram assembly32.

BHA24further includes actuators371-nthat selectively apply a cumulative force against the housing26, and an opposing force against ram assembly32. More specifically, actuators371-nofFIG. 1are made up of reactive members381-n, that in the illustrated embodiment are disposed in housing26. Further illustrated is that each of the reactive members381-nhave an end that is coupled with the housing26via contact with an associated bulkhead301-n. Examples of the reactive members381-ninclude things that change in size or shape. Embodiments exist where the change in size or shape is in response to applied energy, such as electricity or magnetism; or introducing a fluid to the actuators371-nsuch as hydraulic or pneumatic. Changes in size include becoming longer, shorter, wider, thinner, or combinations thereof. Example constituents of the reactive members381-ninclude electro-active materials, magnetostrictive materials, magneto-active materials, lead-zirconate-titanate, lead-magnesium-niobate, terfenol-D, galfenol, and combinations thereof. An opposing end of each of the reactive members381-ncouples with the ram assembly32via resilient members401-nwhere each of the resilient members401-nare in contact with the ram assembly32. In the example ofFIG. 1, resilient member401abuts a drill chuck42shown formed on a lower end of ram assembly32. As will be described in more detail below, ram assembly32and drill chuck42are recriprocatable with respect to the housing26and drill pipe20portion of the drill string16. In the illustrated example, resilient member402mounts on radial wall341, resilient member403mounts on radial wall342, and resilient member40mounts on radial wall34n. Examples of the resilient members401-ninclude springs, Belleville washers, elastomeric members, combinations thereof, and the like. In an alternate embodiment, resilient members401-nare not included so that the ends of the reactive members381-ndirectly contact the ram assembly32.

A drill bit44is shown mounted to drill chuck42on an end of drill chuck42that is opposite from its connection to ram assembly32. Drill bit44is equipped with cutters46on its cutting face for excavating wellbore12. Further shown inFIG. 1, is a controller48which connects to a communication means49for communicating signals and/or electrical power to the reactive members381-n. In one example of operation, reactive members381-nrespond to applied electrical energy (such as that provided from controller48via communication means49) by elongating, which imparts a force against the housing26, and another force against ram assembly32that is in a direction opposite to the force applied to the housing26. Embodiments exist where controller48includes a power supply (not shown) from which electricity is selectively provided to reactive members381-n. In an alternate embodiment, a dedicated power supply50is shown with an output line connecting to communication means49and through which electricity is routed downhole. An interface51between the controller48and power supply50provides communication from controller48to power supply50for providing electricity to communication means49. It should be pointed out that ram assembly32is axially movable with respect to housing26, so that the oppositely directed forces applied by the reactive members381-nto the housing26and ram assembly32causes ram assembly32to move axially with respect to housing26. In one example, the applied forces of the reactive members381-naxially urges the ram assembly32, thereby axially moving drill chuck42and drill bit44in a direction away from drill string16and towards the bottom of the wellbore12. Further, the axial movement of the drill bit44is with respect to the rest of the drill string16, increases the force exerted by the drill bit44against the bottom of wellbore12to above that of the weight on bit.

Thus selectively generating forces against ram assembly32with reactive members381-ncan generate a reciprocating motion of bit44against the bottom of wellbore12, wherein the resultant force is greater than the standard weight on bit that takes place during a normal drilling operation. An advantage of the strategic combination of the reactive members381-nwithin housing26and ram assembly32creates a resultant force on the ram assembly32, and thus drill bit44, which is cumulative of the forces generated by each of the reactive members381-n. Moreover, the axial displacement of the ram assembly32with respect to the rest of the drill string16is about that of an axial extension of a single one of the reactive members381-nrather than a sum of all of their elongations. In one example, controller48energizes actuators371-nat designated intervals of time, and at designated durations of time, so that the frequency at which the bit44strikes the bottom of the wellbore12is at a designated frequency. Examples of designated frequencies are a resonant frequency of the drilling system10, a resonant frequency of the rock making up the formation14, or a combination thereof. Resonance is a phenomenon seen by some cyclical systems, whereby energy from one cycle is stored by the system and used in the next cycle. In one example of the drilling system10described herein, recycling of energy between cycles allows for a greater impact force of the percussive elements than could be achieved for a non-resonant percussive system using the same energy input. It is well within the capabilities of one skilled in the art to operate controller48so that the actuators371-nare energized at the designated time intervals and durations so the bit44strikes the bottom of the wellbore12at the designated frequency.

The high frequency vibration imparted against the formation14creates a series of impacts that cause compressive failure of the formation14under load, which is in addition to the shear failure caused by rotating the bit44while in contact with the formation14. Tuning the frequency of vibration of the drilling system10to a resonance mode increases drilling efficiency above that of operating at a range of different frequencies, or by rotating the drill string16alone. An advantage of the arrangement shown is that although the actuators371-nare arranged in series, the resulting force is as though the actuators371-nwere in parallel, that is, the resulting force is substantially equal to the sum of force exerted by each of the actuators371-n. Moreover, in an example the axial displacement of the bit44, due to the cumulative axial displacement of the actuators371-nis substantially the same as if the actuators371-nare in parallel. In an embodiment, the Young's modulus of the rock making up the formation14can be inferred from the frequency of vibration of the BHA24, as the stiffness of the rock will have an effect on the resonant frequency of the system10.

The velocity of the mass m of the bottom hole assembly24changes by Δv during impacts of the oscillator of period τ, due to the contact harmonic force F=Pdsin(πt/τ) which is governed by Equation 1, for the changing momentum of the system.

In one example, the uniaxial compressive strength of a rock is defined as the value of the peak stress sustained by a rock specimen subjected to failure by uniaxial compression. It is the maximum load supported by the specimen during the test divided by the effective contact area subjected to the compression. Thus the compressive strength of the rock;

where Aeis the effective area, which in an example is assumed to be about 5% of the area of the hole drilled.

Assuming that the drill bit44performs a harmonic motion between impacts, in this example the maximum velocity of the drill bit is Vm=Aω, where A is the amplitude of the vibration and ω=2πf is its oscillation frequency in rad/s. Assuming further that the impact occurs when the drill bit44has maximum velocity Vmand that the drill bit44stops during the impact, then Δv=Vm=2Aπf. Accordingly in this example, the vibrating mass is expressed as:

The period of the impact, τ, in the above expression can be determined by many factors including the material properties of the formation14and the bottom hole assembly24, other factors include the frequency of impacts. In one example of operation, τ is estimated to be about 1.0 percent of the period of oscillation, that is, τ=0.01/f. By substituting τ into Equation 4 a lower bound estimation of the resonant frequency that can provide enough impulse for the impacts is given by Equation 5 as follows.

In an example, Equation 5 provides a lower bound estimate for the stable frequency of the oscillator. The use of a frequency too much greater than this lower bound frequency can generate a crack propagation zone in the formation14that is in front of the drill bit44during operation, which could lead to compromise borehole stability and reduced borehole quality. Moreover, if the oscillation frequency is too large then accelerated tool wear and failure may occur. A scaling/safety factor, Sf, with appropriate value less than 1.0 can be applied to the frequency as a precautionary measure.

The dynamic force, Pd, applied to the oscillation system can be calculated by rearranging Equation 2 and can be expressed as follows:

where in this example Deis an effective diameter associated with effective area (Ae) of the rotary drill bit44which is the diameter, D, of the drill bit44scaled according to the fraction of the drill bit44which contacts the material being drilled. Thus in this example, the effective diameter, De, can be defined as:

where SCis a scaling factor corresponding to the fraction of the drill bit44which contacts the material being drilled. For example, estimating that only 5% of the drill bit surface is in contact with the material being drilled, De=√{square root over (0.05)}D. An appropriate value of scaling/safety factor can be introduced to the dynamic force, Pd, according to the material being drilled so as to ensure that the crack propagation zone does not extend too far from the drill bit44, and consequently compromising borehole stability and reducing the borehole quality.

Another factor to consider is that the resonant frequency changes when drilling through different rock types. The compressive strength can be related to an optimal frequency range. It was therefore considered that the lower frequency range can be in relation to changing rock properties, looking at the right hand side of Equation 5 and introducing a factor, Sf.

Referring now toFIG. 2, shown in a side sectional view is an alternate example of a drilling system10A used in forming a wellbore12A in a formation14A. In this example, the drilling system10A includes many of the same elements of the drilling system10ofFIG. 1, that is, a drill string16A in the wellbore12A, a rotary table18A, drill pipe20A, a derrick22A, a BHA24A having a housing26A, and sidewalls27A on the housing26A. Further making up the BHA24A are compartments28A1-nthe housing26A, and bulkheads30A1-nat opposing axial ends of the compartments28A1-nA generally cylindrically shaped ram assembly32A is coaxially disposed in the housing26A having axial sidewalls33A and radial walls34A1-nthat are transversely mounted within sidewalls33A. Axially between the radial walls34A1-nare compartments36A1-nwhich actuators37A1-nare provided and that include reactive members38A1-nResilient members40A1-nprovided in the compartments36A1-nexert a biasing force against reactive members38A1-n.

A difference between the embodiments ofFIGS. 1 and 2concerns the bit44A. As shown, bit44A is made up of a main bit52A having an axial bore54A extending therethrough. An inner bit56A is included with the main bit52A that reciprocates within bore54A. Here, the inner bit56A has an upstream end that attaches to a lower end of ram assembly32A via a connecting rod58A. Thus, in this example, actuating the reactive members38A1,38A2, . . . ,38Angenerates a resultant force in ram assembly32A which transfers only to inner bit56A to reciprocate it within the main bit52A. Further, main bit52A is shown mounted to a lower end of housing26A.

Because housing26A is not axially motivated by actuators37A1-n, main bit52A does not axially reciprocate in response to operation of actuators37A1-nand thus generally maintains its axial distance from the lower end of drill string16A. Instead, main bit52A is limited to rotation within wellbore12A, much like a standard drill bit. Further, cutters60A,62A are shown respectively formed on the downhole ends of inner bit of56A and outer or main bit52A. In bits that rotate about their axes, the radial speed of the bit, and thus the cutters on the bit, becomes lower with proximity to the bit axis. Meaning the region of a bit proximate its axis is less effective for rotational drilling that regions of the bit distal from the bit axis. An advantage of focusing the axial vibration of the effective bit area towards its inner radius is that when the cutters60A on the inner bit56A are out of contact with the formation14(due to reciprocation of the inner bit56A), the amount of cutting force per bit surface area lost is less than that if an outer portion of the bit44A is moved away from the formation14. As such, adding the axial vibration and forces on the ensuing rock enhances the operational functionality of the bit44A ofFIG. 2. Examples exist where cutters60A,62A are formed from composites, such as poly-crystalline diamond.

FIG. 3is an axial sectional view of an example of the BHA24taken along lines3-3ofFIG. 1. In this example, a coil64is shown between ram assembly32and reactive member381. As is known, selectively energizing the coil64with electricity generates an electrical field that as explained above axially elongates the reactive member381. Electricity for energizing the coil64can be from surface, such as from controller48or power supply50(FIG. 1), from a battery (not shown) included with the bottom hole assembly24, or from a downhole generator (not shown) that converts fluid flow to electricity. As shown reactive member381coaxially inserts into a sleeve66that can provide protection/isolation for the reactive member381. Further illustrated are supports68that extend radially between the ram assembly32and housing26. Annular spaces70are defined in the circumferential spaces between adjacent supports68and the radial spaces between the ram assembly32and housing26. In an example of operation, drilling fluid flows downhole within the annular spaces70, and back uphole within an annulus72between the outer surface of the housing26and walls of the wellbore12.

FIGS. 4A and 4Bprovide in a side sectional view an example of how the drill bit44of the drilling system10reciprocatingly contacts the bottom74of the wellbore12, thereby creating fractures in the formation14. Referring specifically toFIG. 4A, here the drill string16of the drilling system10is disposed in the wellbore12in a retracted mode so that the bit44is spaced away from a bottom74of the wellbore12. In the retracted mode, the members381-nare in an unelongated state. In an example where members381-nare magnetostrictive material, the members381-nare not energized and electricity from controller48or power supply50is not being transmitted to the members381-n. Referring now toFIG. 4B, the members381-nare depicted in an elongated state. In an embodiment where the members381-nare made from magnetostrictive material, the elongation can be due to applied electricity, such as from controller48A or power source50. In the elongated state ofFIG. 4B, the members381,382,383, and38n, have elongated over their lengths shown inFIG. 4Aby the respective distances D1, D2, D3, and Dn.

Further illustrated is that the bit44has moved a distance DBITin the wellbore12. As described above, the movement of the bit44is in response to movement of the members381-nvia the coupling between the members381-nand ram assembly32(FIG. 1). Additionally, in one example, the distances D1, D2, D3, and Dn(that can be referred to as designated distances) all have substantially the same value. Further in this example, distance DBIThas a value that is substantially the same as the value of any one of distances D1, D2, D3, and Dn. Accordingly, in this example, the novel configuration of the housing26and ram assembly32results in the distance DBITnot being a sum of the individual distances D1, D2, D3, and Dn.

Further illustrated inFIG. 4Bare arrows that respectively represent forces F381, F382, F383, and F384generated by the members381-nwhen being actuated/elongated. Another arrow represents force FBIT which is the force being transmitted to drill bit44from elongation of the members381-n, and which is substantially equal to a summation of forces F381, F382, F383, and F384. As indicated above, ends of the members381-ncouple with the housing26, and opposing ends of the members381-ncouple with the ram assembly32. Thus the ram assembly32, the attached drill chuck42, and drill bit44, are moved away from the housing26and drill pipe20by elongating the members381-n. Strategically coupling the members381-nwith the ram assembly32via the radial walls341-nand housing26via the bulkheads301-nallows for reciprocation of the drill bit44a distance substantially the same as the elongation of individual members381-nwhile also exerting a cumulative force onto drill bit44so that its reciprocating force FBITis substantially the same as the sum of forces F381, F382, F383, and F384. An advantage of reciprocating the drill bit44, while also rotating the drill bit44, is that when the drill bit44is reciprocatingly thrust against the bottom74of the wellbore12, fractures76are formed in the formation14adjacent the bottom74of the wellbore12. The fractures76can reduce inherent stresses in the formation14, which increases the amount of rock removed with each rotation of the drill bit44, that in turn increases rate of penetration of the drilling operation.

FIGS. 5A and 5Bshow in a side sectional view an example of reciprocating motion of the drill bit44A ofFIG. 2. In the example ofFIG. 5Athe drill string16A is in the retracted configuration with the members38A1-nin an unelongated state. Further, the inner bit56A is spaced upward from the bottom74A of the wellbore12A with its cutters60A out of contact with the bottom74A, while the main bit52A is at the bottom74A of the wellbore12A and its cutters62A in rotating contact with the bottom74A. In an example where members38A1-ninclude magnetostrictive material, the members38A1-nare not energized and electricity from controller48A or power supply50A is not being transmitted to the members38A1-n.

In the example ofFIG. 5B, the members38A1-nare depicted in an elongated state. In an embodiment where the members38A1-nare made from magnetostrictive material, the elongation can be due to applied electricity, such as from controller48A or power supply50A. In the elongated state the members38A1,38A2,38A3, and38An, have lengthened over that of their lengths inFIG. 5Aby the respective distances D1A, D2A, D3A, and DnA. Further illustrated is that the inner bit56A has moved a distance DBITAwith respect to the main bit52A. In this example the main bit52A is coupled with the housing26A by a threaded connection78A, and unlike the inner bit56A, the main bit52A does not reciprocate with movement of the ram assembly32A. As described above, the movement of the inner bit56A is in response to movement of the members38A1-nvia the coupling between the members38A1-nand ram assembly32A (FIG. 2).

Additionally, in one example, the distances D1A, D2A, D3A, and DA(that can be referred to as designated distances) all have substantially the same value. Further in this example, distance DBITAhas a value that is substantially the same as the value of any one of distances D1A, D2A, D3A, and DnA. An advantage to reciprocating a portion of the cutting surface of the bit44A proximate the axis AXis that the portions of the cutting surface proximate the axis AXhave a reduced excavating effectiveness than those portions of the cutting surface distal from the axis AX. The bit44A therefore can remain substantially effective in excavating even when the inner bit56A is spaced away from the bottom74A (FIG. 5A). Moreover, the main bit52A is shown creating fractures76A in the formation14A adjacent the bottom74A, which can improve the excavating efficiency of the bit44A as a whole.

In embodiments where the actuators371-n,37A1-n, do not include the members381-n,38A1-nthe distances DBIT, DBITAwill be substantially the same as elongation of one of the individual actuators371-n,38A1-nrather than a sum of their distances. Similarly, the corresponding forces FBIT, FBITAon the bits44,44A will be substantially the same as the sum of forces from the extended actuators371-n,37A1-nwhen the actuators371-n,37A1-ndo not include the members381,38A1-n.

The embodiments described above are well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent. While a presently preferred embodiment has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the embodiments disclosed herein and the scope of the appended claims.