Background

The invention relates generally to the field of dual drill pipe strings. More specifically, the invention relates to mud lift pumps that can form part of a dual drill string.

It is known in the art of subsurface wellbore chilling to use a single pipe string, two parallel pipes or two nested or concentric pipe strings. Concentric or nested pipe strings refer to a string consisting of inner pipe joints arranged within outer pipe joints connected end to end.

In concentric or nested drill strings, the inner pipe forms part of a flow bore extending from the surface to a drill bit at the lower end of the drill string. An annulus between the outer pipe and inner pipe forms part of a second flow bore extending from the surface to the drill bit.

The term "drilling'' as used herein should be understood to refer to creation of a hole in the subsurface by means of the pipe string. It particularly applies for drilling in the crust of the earth for petroleum recovery, tunnels, canals or for recovery of geothermal energy, both offshore and onshore.

It is also known in the art to control pressure in the wellbore annulus (the annular space between the drill string and the wall of the wellbore by using a pump to lift the returning drilhng fluid U.S. Patent No. 7,913,764 issued to Smith et al. discloses a type of mud lift pump that may be used with conventional single conduit drill strings. Mud lift pumps may be operated to maintain a selected pressure or equivalent circulating density (ECD) in the wellbore.

What is needed is a mud lift (fluid return) pump for use with a dual drill string.

Summary

One aspect of the disclosure is a mud lift pump for a dual drill string. The mud lift pump fox a dual drill string includes an energy in the dual drill string and an energy output in fluid communication with a fluid return flow passage in the dual drill string. A method for controlling pressure in a wellbore having a dual drill string therein includes pumping fluid through a fluid supply passage in the dual drill string. A pump energy input is operated using energy supplied through the dual drill string. The pumped fluid is discharged into the wellbore. Energy is imparted to fluid returned into a fluid return passage in the dual drill string from the wellbore using an energy output of the pump.

Other aspects and advantages of the invention will be apparent from the description and claims which follow.

Brief Description of the Drawings

FIG. 1 shows an example drilling arrangement using a nested or concentric drill pipe string and drill string valves.

FIG. 2 shows an example of one type of mud lift pump that can form part of a dual drill string.

FIG. 3 shows another example of a mud lift pump that can form part of a dual drill string.

FIG. 4 shows another example of a mud lift pump that can be used with a dual drill string.

Detailed Description

In FIG. 1 a nested or concentric dual drill string 1 is shown inserted in a wellbore 17 being drilled through subsurface formations 33. The wall of the wellbore 17 creates an annular space (well annulus 9) between the exterior of the dual drill string 1 and the wall of the wellbore 17. The dual drill string 1 may comprise a dual bore drill pipe consisting of an inner pipe 3 arranged within an outer pipe 2. A supply flow of drilling fluid (e.g., "drilling mud"), shown at A, is introduced through a suitable swivel 24 such as a top drive into an annular bore ("fluid supply flow passage") 4 disposed between the inner pipe 3 and the outer pipe 2. The supply flow of drilling fluid A may be ultimately directed to a drill bit 7 that cuts subsurface formations 33. A return flow of drilling fluid, shown at B is transported from the bottom of the wellbore 17 in an inner bore ("return fluid passage") 5 within the inner pipe 3. In the example shown in FIG. 1, the dual driH string 1 may be arranged with a piston 20 fixed to the dual drill string 1 and in sealing contact with the wall of the wellbore 17. The top drive 24 may also rotate or drive the dual drill string 1. A blow out preventer (BOP) 22 and a rotating control device (RCD) 23 may be arranged at the top of the wellbore 17. By the arrangement of the RCD 23 and piston 20, an isolated space is provided in the upper part of the wellbore 17. In the present example, a fluid may be introduced through a fluid inlet 21 into the isolated space. The introduced fluid provides a pressure to the piston 20, thereby forcing the piston 20 and the dual drill string 1 downwards when drilling is performed. As will be appreciated by those skilled in the art, other arrangements than the piston 20 shown in FIG. 1 may be used for providing a driving force to the dual drill string 1, or may be omitted, wherein the isolated space in the wellbore annulus 9 is closed by the BOP 22 and RCD 23. Thus, the use of the piston 20 in the wellbore annulus 9 is not a limitation on the scope of the present disclosure.

The dual drill string 1 is typically arranged with a flow diverter 6 at a lower end thereof connected to a bottom hole assembly (BHA) 8 holding the bit 7 at a lower end portion of the drill string. The bottom hole assembly (BHA) 8 may be a standard type BHA that can be used with conventional (single flow bore) drill pipe and drilling tools, including, without limitation, hydraulic (mud) motors, drill collars, measurement and/or logging while drilling tools. The flow diverter 6 has a flow passage assembly 10a providing a fluid connection between the fluid supply flow passage 4 of the dual drill string 1 and a channel 14 or channel assembly of the BHA 8. The channel 14 of the BHA 8 is shown in the example of FIG. 1 with the shape of an axial bore, and the flow passage assembly 10a is shown with essentially a Y-shape in an axial cross section. First diverging branches 30 of the Y fit in connection with the fluid supply flow passage 4, and an axial passage part 31 corresponds to the stem portion of the Y and fits in connection with the axial shaped channel 14 of the BHA. The supply flow A exits from the channel 14 into the BHA 8 and thence into the cutting area of the drill bit 7.

From the drill bit 7, the return fluid flow B moves in the well annulus 9 into a return flow passage assembly 10b arranged in the flow diverter 6. The axial cross section of a return flow passage assembly 10b also has a Y shape with second diverging branches 41 opening at one end into the well annulus 9 and an axial passage part 40 connected with the fluid return flow passage 5. The return flow B enters the inlet of the flow diverter return flow passage 10b and returns in the fluid return flow passage 5 of the dual string 1.

The dual drill string 1 may be arranged, for example, with one to four valve elements. Two of the valve elements may be arranged for closing and opening of the fluid supply flow A, and two of the valve elements may be arranged for closing and opening of the fluid return flow B. By such, arrangement of valve elements, a double barrier system may be provided both for the control of the fluid supply flow A and for control of the fluid return flow B. The closing of the valve elements may be performed, in some examples automatically if the drilling system needs to close down, and in case of emergency, for example, a kick or other unwanted well fluid control conditions.

In FIG. 1 example locations of the four valve elements are shown schematically. Two bottom valves 11c, 11c provided for opening and closing the supply flow A, may be located in the bottom hole assembly 8. The bottom valves 11c, lid may be positioned to open and close the channel 14, and one of the bottom valves, e.g., lid, may be positioned to control the opening and closing of the outlet 15 of the channel 14. The other bottom valve 11c may be positioned upstream along the channel 14 within the bottom hole assembly 8. The bottom valves 11c, lid may be conventional drill string check valves as are used with single bore drill string components. Upper valves 11a, lib may be positioned in the dual drill string 1. The upper valves 11a, lib, may be specifically configured to connect within a nested dual drill string, for example, one shown in U.S. Patent No. 3,208,539 issued to Henderson. The valves 11a through lid are only provided as an example configuration and may be omitted in other examples of a dual drill string.

FIG. 2 shows an example mud lift pump 60 that may be included in the flow diverter 6. A motor 50, which may be a positive displacement motor, centrifugal (turbine) motor, or any other type of motor that is operable by the flow of fluid may be disposed in the channel 14 below the position in the flow diverter 6 where the fluid supply passage 4 is diverted from the annular space between the inner pipe (3 in FIG. 1) and the outer pipe (4 in FIG. 1). The motor 50 may convert flow of drilling fluid in the channel 14 into rotational energy. The rotational energy from the motor 50 may be transmitted along a shaft 52. The shaft may pass through the portion of the diverter 6 wherein the flow return passages 10b divert returning drilling fluid flow from the wellbore into the flow return passage 5 in the interior of the inner pipe (3 in FIG. 1). The shaft 52 may be exposed or may be enclosed in a separate tube or conduit (not shown). The shaft 52 maybe rotationally coupled to a pump 54 disposed in the flow return passage 5 above the flow return passages 10b. The pump 54 may be a positive displacement pump, centrifugal (turbine) pump or any other type of pump that converts rotational energy from the shaft 52 into energy in the returning drilling fluid. Such energy may be used, for example, to reduce the hydrodynamic pressure of the returning drilling fluid entering the flow return passages 10b so that a predetermined or selected pressure may be maintained in the wellbore annulus (9 in FIG. 1). It will be appreciated by those skilled in the art that the energy transfer characteristics of the motor 50 and the pump 54 may be selected so that operating the drilling fluid supply flow (A in FIG. 1) at selected rates may provide a selected pressure in the wellbore. For example, it may be desirable to reduce the equivalent circulating density (ECD) of the drilling fluid resulting from hydrostatic pressure of the drilling fluid plus frictional pressure loss in the wellbore. By appropriate selection of energy transfer characteristics of the motor 50 and pump 54, appropriate selection of nozzles or jets in the drill bit (7 in FIG. 1), and flow rate of the drilling fluid, it may be possible to maintain a selected ECD for a particular drilling fluid density ("mud weight").

Another example of a pump 62 is shown in FIG. 3. The pump 62 in FIG. 3 is known as a "jet pump." The jet pump 62 may form part of segments of nested dual drill string at any selected position above the flow crossover (6 in FIG. 1). The jet pump may include a nozzle 4A in hydraulic communication with the fluid supply flow passage 4 disposed between the inner pipe 3 and the outer pipe 4. The nozzle 4A may divert some of the flow from the fluid flow supply passage 4 into a venture or educator 5A disposed in the fluid return flow passage 5 (disposed inside the inner pipe 3). Fluid flow from the nozzle 4A into the venture or educator 5A may reduce the pressure in the fluid flow return passage 5. With appropriate selection of nozzle size, drill bit nozzle size, and venture internal diameter, at selected flow rates of the drilling fluid a selected pressure or ECD may be provided in the wellbore.

Another example of a pump is shown in FIG. 4 at 64. The present example pump 64 may be a turbine-type pump including a first turbine 70 that may be rotatably supported on the exterior of the inner pipe 3A. The first turbine is disposed in the fluid supply flow path (4 in FIG. 1), i.e., in the pipe shown in FIG. 1 the annular space between the inner pipe and the outer pipe. The first turbine 70 may be caused to rotate as a result of fluid being pumped through the fluid supply flow path (4 in FIG. 1). A second turbine 66 may be rotatably mounted on the interior of the inner pipe 3A. The second turbine 66 may include a flow deflector 68 at its center to decrease fluid friction by reason of flow of fluid in the fluid return flow path (5 in FIG. 1).

In the present example, the first turbine 70 and the second turbine 66 may be magnetically coupled so that rotation of the first turbine 70 causes corresponding rotation of the second turbine 66. Magnetic coupling between the first and second turbines may be direct or may include any form of magnetic gearing to change the ratio of rotational speeds of the first and second turbines. Example magnetic gear arrangements are shown in U.S. Patent Application Publication No. 2010/0032952 filed by Hatch et al. Energy of the pumped fluid in the fluid supply flow path (4 in FIG. 1) may thus be transferred to the fluid flow in the fluid return flow path (5 in FIG. 1). The number of blades, blade pitch, blade length and other design parameters of the turbines 66, 70 may be selected to transfer a selected amoxint of energy from the fluid supply flow to the fluid return flow. By appropriate selection of the fluid flow rate in the fluid flow supply path (4 in FIG. 1) turbine parameters and, for example, nozzle sizes in the drill bit (7 in FIG. 1), a selected fluid pressure may be maintained in the wellbore (17 in FIG. 1). Such pressure may be selected to correspond to a selected equivalent circulating density as with the other example pumps described above.

In the present example, if magnetic coupling is used to transfer rotational energy from the first turbine 70 to the second turbine 66, it is preferable that the inner pipe 3A be made from a non-magnetic material. More preferably, the inner pipe may be made from a non-magnetic and electrically non-conductive material such as ceramic or certain compositions of glass, or fiber reinforced plastic. By using such material, magnetic coupling will be made effective between the turbines, and will result in low eddy current generation by reason of rotation of magnets (not shown) that couple rotation of the first turbine 70 to the second turbine 66. An inner pipe made from such materials may be covered by a thin layer of non-magnetic metal, such as monel or various alloys sold under the trademark INCONEL, which is a registered trademark of Huntington Alloys Corporation, Huntington, WV. A possible structure for a metal covered, ceramic or glass pipe structure is shown in U.S. Patent Application Publication No. 2011/0234035 filed by Wittschier.

If required, more than one of the pumps shown in FIGS. 3 and 4 may be included in the dual drill string. It is also possible to combine the pump shown in FIG. 2 with one or more of the pumps shown in FIG. 3 in other example configurations of a dual drill string.

The foregoing example of a dual drill string, in which an inner pipe is nested within an outer pipe is not a limitation on the scope of the present disclosure. In other examples, the pipes may be side by side. In still other examples, the pipe may be a dual conduit coiled tubing. An example of such coiled tubing is described in U.S. Patent No. 5,285,204 issued to Sas-Jaworsky. The pipe may also include one or more electrical conductors, for example, as described in U.S. Patent Application Publication No. 2012/0125686 filed by Hogseth et al.

For purposes of describing the function of the various forms of pumps that may be used with a dual drill string according to the disclosure, the pump may be generally described as having an energy input from any source, including a device in fluid communication with the fluid flow supply passage or electrical power, and an energy output in fluid communication with the fluid flow return passage, such that energy is transferred from the energy input to the fluid return flow. For example, the motor shown in FIG. 2 may be an electric motor, and may receive power for operation thereof from electrical conductors in a dual pipe string as described in the '686 publication cited above.

While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.