WO2012027271A2

WO2012027271A2 - Counter rotating drilling system

Info

Publication number: WO2012027271A2
Application number: PCT/US2011/048617
Authority: WO
Inventors: David A. H. Wells
Original assignee: Wells David A H
Priority date: 2010-08-26
Filing date: 2011-08-22
Publication date: 2012-03-01
Also published as: WO2012027271A3

Abstract

A drilling system (10) includes a gear box (20) with a first mandrel (30) having a gear-profiled spline portion (35) and connectable at its upper end (31) to a shaft of a down hole motor and at its lower end (35) to a first drill bit; a second mandrel (50) having one or more spaced-apart rotators (65) with a gear-profiled spline portion (67) and connectable at its lower end (53) to a second drill bit; and a housing (80) having a gear-profiled spline portion (80) and connectable to a body of the down hole motor. When the gear box (20) is engaged in a drilling operation, the first mandrel (30) rotates in a same direction of rotation as the shaft of the down-hole motor, the housing (80) is prevented from rotating relative to the shaft, and the rotators (65) of the second mandrel (50) rotate in a direction opposite that of the first mandrel (30). A substantially zero net torque is experienced by the down-hole motor.

Description

COUNTER ROTATING DRILLING SYSTEM

BACKGROUND OF THE INVENTION

This invention relates generally to systems and apparatuses used in drilling holes for oil and gas exploration and production. More specifically, the invention relates to a modification to down-hole drilling motors so that the holes drilled with these motors are less likely to wander away from a straight line.

When drilling holes into the Earth's various formations, drill bits of different sizes, shapes and materials are attached to the end of drill pipe and placed against the formations. The drill bits are then rotated either directly from the surface or by down- hole motors located between end of the drill Pipe and the drill bit. The combination of the load and the rotation causes the rock to break up. The broken up pieces are then removed from the well bore by drilling fluids.

Currently, the only available method of drilling wells is with a single bit assembly. Due to the torque generated against the rock formations, the single bit assembly tends to wander away from a straight line (which is usually not desired), and most "straight" holes are in fact not straight. Where a truly straight hole is required, "controlled drilling" methods are employed. However, those methods are expensive and cause delays in overall drilling times. Therefore, a need exists for a simple, reliable and cost-effective drilling system that improves hole straightness. SUMMARY OF THE INVENTION

A drilling system made according to this invention includes a gear box with three main parts: (1) a first mandrel having a gear-profiled spline portion and connectable at its upper end to a shaft of a down hole motor and at its lower end to a first drill bit; (2) a second mandrel having one or more spaced-apart rotators with a gear-profiled spline portion, which may be housed in a cage, and connectable at its lower end to a second drill bit; and (3) a housing having a gear-profiled spline portion located and connectable to a body of the down hole motor. The first mandrel resides within a perimeter of the rotators of the second mandrel, the second mandrel resides within a perimeter of the housing, and each gear-profiled spline portion meshes with an opposing gear-profiled spline portion. Sealing means prevent external drilling fluids from contacting the gear- profiled spline portions and balancing means balance the internal oil pressure with that of the external drilling fluids.

When the gear box is engaged in a drilling operation, the first mandrel rotates in a same direction of rotation as the shaft of the down-hole motor, the housing is prevented from rotating relative to the shaft of the down-hole motor, and the rotators of the second mandrel rotate in a direction opposite that of the first mandrel. A substantially zero net torque is experienced by the down-hole motor.

Objects of this invention are to (1) enable bore holes to be drilled straight without having to apply other measures to correct the inherent problem of wandering with existing single bits; (2) enable the use of two concentric drill bits and to cause them to rotate in opposing directions for drilling holes into the earth's various formations; (3) greatly reduce the net torque experienced at the top of the motor when drilling, which is of special advantage when drilling with coiled tubing; and (4) provide a drilling system that is quite simple with relatively few moving parts that are well protected from drilling fluids. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-section front elevational view of a preferred embodiment of a gear box used in a counter rotation drilling system made according to this invention. The gear box includes an inner mandrel which is connectable to the shaft of a down-hole motor, an outer mandrel, and a housing which is connectable to the body of the down- hole motor.

FIG. 2 is a view of the gear box of FIG. 1 taken along section line 2-2 of FIG. 1. The gear-profiled spline portions of the inner mandrel mesh with those of the outer mandrel and the gear-profiled spline portions of the outer mandrel mesh with those of the housing. Because the inner mandrel is connected to the shaft of the down-hole motor, and because the housing is prevented from rotating relative to the motor, a counter- rotation effect is achieved between the inner and outer mandrels.

FIG. 3 is cross-section, front elevational view of the gear box of FIG. 1 with the inner mandrel removed. The rotators of the outer mandrel reside between pillars which form a cage located toward the upper end of the outer mandrel, A retaining plate and bearing ball arrangement keeps the outer mandrel aligned with the housing.

FIG. 4 is a partial cross section front elevational view of the housing of the gear box of FIG. 1.

FIG. 5 is a front elevational view of the cage portion of the outer mandrel of the gear box of FIG. 1.

FIGS. 7 to 9 are front, top and bottom views, respectively, of the retaining plate which retains the cage portion of the outer mandrel of the gear box of FIG. 1. is a top view of the cage portion of the outer mandrel of the gear box of FIG. 1

FIG. 10 is a table which presents examples of the relationship between the drive and inner mandrel, cage and outer mandrel, and the housing. Elements and numbering used in the drawings and detailed description:

10 Drilling system 61 Retaining plate

20 Gear box 62 Recess

30 First or inner mandrel 63 Thrust bearing

31 Upper end 65 Rotator

33 Lower end 67 Gear-profiled spline

35 Gear-profiled spline 69 Axle system

37 Seal area 73 Retaining sleeve

39 Two-way floating seal 75 Pillar

41 Central bore 77 Oil seat or seal plate

43 Splined section 79 Connection to second or outer bit

45 Connection to shaft 80 Housing

47 Connection to first or inner bit 81 Upper End

50 Second or outer mandrel 83 Lower End

51 Upper end 85 Internal diameter

53 Lower end 87 Gear-profiled spline

55 Semi-circular groove for 93 89 Semi-circular groove for 93

57 Cage 91 Seal

58 Recess 93 Bearing ball

59 Longitudinal slots 95 Hole for 93

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A drilling system 10 made according to this invention enables the use of two concentric drill bits (not shown) which rotate in opposing directions during drilling operations. By providing this counter-rotation, the tendency of one drill bit to wander in one direction is countered by the tendency of the other drill bit to wander in the opposite direction, thereby resulting in holes that are drilled straighter than current single bit assemblies.

In order to be able to achieve this result, and referring first to FIG, 1, a gear box convertor ("gear box") 20 is employed onto which the two drill bits are attached at one end and a down-hole motor of a type well-known in the art (not shown) is attached at the other end. The shaft of the down-hole motor inputs rotation in one direction and the gear box 20 provides two concentric counter rotating mandrels 30, 50. The first or inner drill bit of the two drill bits is attached to the first or inner mandrel 30 and the second or outer drill bit is attached to the second or outer mandrel 50. In order to have substantially equal torque produced by each drill bit, the bit surface areas and rotation speeds must be taken into account {see e.g. FIG. 10).

The gear box 20 consists of three main parts: inner mandrel 30, outer mandrel 50, and housing 80. The inner mandrel 30, which is also the drive mandrel, is a hollow mandrel that, at its upper end 31 , connects to the shaft of the down-hole motor and, at its lower end 33, connects to the inner drill bit. A section 43 of the inner mandrel 30 includes gear-profiled splines 35. Above and below the spline section 43 are seal and bearing areas {see e.g. two-way floating seal 39 in seal area 37) and, on each end 31, 33, the connections 45, 47 to the shaft of the down-hole motor and the inner drill bit, respectively. The central bore 41 of the inner mandrel 30 receives the drilling fluid that powers the down-hole motor. The inner mandrel 30 resides within the outer mandrel 50. A retaining sleeve 73 located toward the lower end 33 of the inner mandrel 30 surrounds the inner mandrel 30.

The outer mandrel 50 includes a cage 57, located at its upper end 51, which is formed by longitudinal slots 59 and pillars 75 left by the longitudinal slots. Three or more rotators 65 are located within longitudinal slots and are received by a retaining plate 61 that is bolted to the pillars 75. The rotators 65 are solid bars with gear-profiled splines 67 machined along their lengths and axle systems 69 on each end 51, 53 that fit, with bearings, into recesses 58, 62 of the cage 57 and the retaining plate 61 , respectively. The lower end 53 of the outer mandrel 50 includes seal areas (see e.g. two-way floating seal 39) and the connection 79 for the second or outer drill bit.

Housing 80, which connects at its upper end 81 to the body of the down-hole motor, has gear-profiled splines 87 machined on part of the internal diameter 85. Semicircular grooves 55, 89 on the outer mandrel 50 and the housing 80, respectively, accommodate bearing balls 93 that are inserted through holes 95 in the housing 80 to hold the mandrel 50 and housing 80 together axially while allowing rotation relative to each other. The lower end 83 of the housing 80 has seals 91 that act against the outer mandrel 50 to prevent drilling fluids entering the gear box 20.

When assembled, the gear-profiled splines 35, 67, 87 on the drive mandrel 30 , the rotators 65 and the housing 80 mesh together. Therefore, when the shaft of the down-hole motor rotates, the drive mandrel 30 and rotators 65 rotate. As the rotators 65 mesh with the housing— which cannot rotate because it is connected to the static body of the down-hole motor— the cage and outer bit mandrel 50 rotate instead, in a direction opposite to that of the drive mandrel 30.

The inner bit load is transmitted by the drive mandrel 30 directly to the shaft of the down-hole motor. The outer bit load is transmitted by the cage and outer mandrel 50 through a thrust bearing 63 to the body of the down-hole motor. The thrust bearing 63 is located between the retaining plate 61 of the cage 57 and an oil seat or seal plate 77. If desired, this load could be divided between the shaft of the down-hole motor and the body of the down-hole motor.

Seal systems totally enclose the gear box 20. The gear box 20 is filled with oil so none of the gear-profiled splined sections 35, 67, 87, nor any of the bearings 93, are exposed to drilling fluids. The flow of the drilling fluid from the down-hole motor could be directed to both the inner and outer bits through flow passages (not shown). A two- way floating seal system 39 balances the internal oil and external drilling fluids pressures.

FIG. 9 presents examples of the relationship between the housing 80, rotator 65, and mandrel 30 for various sizes of gear boxes 20. For example, a counter rotating drilling system 10 comprised of a 6-1/2 inch (16.51 cm) gear box, with a 2-3/8 inch (6.032 cm) box thread for the inner bit and a 4-1/2 inch (11.43 cm) pin thread for the outer bit, has an inner diameter of the gear-profiled splines 87 on the housing 80 of about 5 inches (12.7 cm), an outer diameter of the drive mandrel 30 of about 3 inches (7.62 cm), and an outer diameter of the rotators 65 of about 1.3 inches (3.302 cm). With gear teeth depths of 3/16 of an inch (.476 cm) and 6 teeth per inch, the rotation-to-speed ratio works out at about 1.8. In order to balance the torques for an 8-1/2 inch (21.59 cm) outside diameter outer drill bit, the inner drill bit would have an outer diameter of about 5.6 inches (14.224 cm). Allowing for space between the pillars 75 of 10% more than the diameter of the rotators 65, five rotators 65 can be used. The five rotators 65 take up about 60% of the mean diameter of the cage 57, leaving about 40% as the pillars 75.

By having two drill bits, sized with the rotational speed of each considered, the torque generated by each bit will be substantially equal and opposite, and thus there will be zero net torque. This means that the tendency for the bit assembly to wander is eliminated, and wells will be drilled straight, in the direction that the bits are pointed. The counter-rotating drill bits are made possible by the gear box 20 described above.

A counter rotating drilling system 10 made according to this invention may be used in any application in which bore holes or wells are required to be drilled straight. Although the system requires the use of a down-hole motor, use of a down-hole motor is less expensive than contracted controlled drilling packages.

The counter rotation drilling system 10 also has application where thin walled and coiled pipes are used. These pipes have very low torsional strengths, so their use for drilling is very restricted. By using the system in conjunction with a down-hole motor, these types of pipes can be used for drilling, as there is zero net torque at the top of the down-hole motor to which the pipes would be connected.

While a counter rotation drilling system has been described with a certain degree of particularity, many changes may be made in the details of construction and the arrangement of components without departing from the spirit and scope of this disclosure. A counter rotation drilling system made according to this invention, therefore, is not limited to the embodiments described herein but is limited only by the scope of the claims, including the full range of equivalency to which each element thereof is entitled.

Claims

WHAT IS CLAIMED IS:

1. A drilling system (10) comprising:

a gear box (20) having including

a first mandrel (30) having a gear-profiled spline portion (35) located between an upper (31) and lower end (33) of the first mandrel (30), the first mandrel upper end (31) being connectable to a shaft of a down hole motor and the first mandrel lower end (33) being connectable to a first drill bit;

a second mandrel (50) having one or more spaced-apart rotators (65), each of the one or more spaced apart rotators having a gear-profiled spline portion (67) located between an upper (51) and lower end (53) of the second mandrel, the second mandrel lower end (53) being connectable to a second drill bit; a housing (80) having a gear-profiled spline portion (87) located between an upper (81) and lower end (83) of the housing, the housing upper end (81) being connectable to a body of the down hole motor; when in an assembled state, the first mandrel (30) residing within a perimeter of the one or more rotators (65) of the second mandrel (50), the second mandrel residing within a perimeter of the housing (80), each gear-profiled spline portion (35, 67, 87) meshing with an opposing gear- profiled spline portion (35, 67, 87).

A drilling system according to claim 1 , when the gear box is in a drilling state, the first mandrel connected to the shaft of the down-hole motor and rotating in a same direction of rotation as the shaft of the down-hole motor, the housing being connected to the body of the down-hole motor and prevented from rotating relative to the shaft of the down-hole motor, the one or more spaced-apart rotators of the second mandrel rotating in a direction opposite that of the first mandrel.

A drilling system according to claim 2 wherein a substantially torque is experienced by the down-hole motor.

A drilling system according to claim 3 further comprising a thrust bearing arranged to transmit a load caused by the second drill bit to the body of the down-hole motor.

A drilling system according to claim 2 wherein the down hole motor located between an end of a drill pipe and the first and second drill bits.

A drilling system according to claim 1 further comprising the gear box having sealing means for preventing exposure of each gear-profiled spline portion to external drilling fluids.

7. A drilling system according to claim 6 further comprising means for balancing an internal oil pressure with a pressure of the external drilling fluids.

8. A drilling system according to claim 7 wherein the balancing means include a two-way floating seal located between the first mandrel and the second mandrel.

9. A drilling system according to claim 1 further comprising bearing means located between the second mandrel and the housing.

10. A drilling system according to claim 1 further comprising the first mandrel having a central longitudinal bore in communication with a source of drilling fluid to power the down hole motor.

11. A drilling system according to claim 1 further comprising a cage located at an upper end of the second mandrel, the cage including spaced-apart pillars, each rotator in the one or more spaced-apart rotators being spaced apart from an adjacent rotator by a pillar in the spaced-apart pillars.