DOWN HOLE PUMP WITH COMPRESSOR

Abstract: Apparatus for compressing a fluid comprising a tubular, open-ended housing (2) having a suction end (5) and a discharge end (6), a tubular, open-ended rotor (8) rotatably arranged in the housing (2), an annular driver space (17) which is defined between the inner surface of the housing (2) and the outer surface of the rotor (8), an annular seal preventing fluid flow from the annular driver space (17) to the suction end (5), a rotor driver (20) arranged in the annular driver space (17), and a rotor-driven compressor (30) arranged in the tubular rotor (8), wherein the rotor-driven compressor (30) includes a helical screw blade (32) which is secured to the inner surface of the tubular rotor (8), and wherein the pitch of the helical screw blade (32) decreases in the direction of the discharge end (6).

Description: The present invention relates recovering a fluid from an underground fluid-bearing formation, wherein a borehole extends from surface to the underground formation, and wherein the fluid is passed to surface through a tube extending through the borehole from the underground formation. In the specification the word "reservoir" will be used to denote an underground fluid-bearing formation. The fluid in the underground formation can be present in the form of a super-critical fluid, a gas, or a mixture of gas and liquid. The fluid can consist of carbon dioxide, natural gas or a mixture of hydrocarbons. The present invention relates more in particular to an apparatus for compressing a fluid, which apparatus can be arranged in the lower end part of the tube which extends through the borehole. U.S.A. patent specification No. 4 684 335 discloses an apparatus for compressing a fluid including a twin rotor screw compressor. French patent specification No. 912 181 discloses an apparatus according to the preamble of claim 1 for compressing a fluid comprising a tubular, open-ended housing having a suction end and a discharge end, and a rotor-driven compressor including a helical screw blade, wherein the pitch of the helical screw blade decreases in the direction of the discharge end. In the known apparatus, the rotor driven compressor comprises a helical screw blade mounted on a shaft which is rotatably arranged in the housing. To drive the shaft use is made of an external rotor driver in the form of an electric motor or a steam turbine. It is an object of the present invention to provide a more compact apparatus from compressing a fluid. To this end the apparatus for compressing a fluid according to the present invention is characterized in that the apparatus further comprises a tubular, open-ended rotor rotatably arranged in the housing, an annular driver space which is defined between the inner surface of the housing and the outer surface of the rotor, an annular seal preventing fluid flow from the annular driver space to the suction end, and a rotor driver arranged in the annular driver space, and in that the rotor-driven compressor is arranged in the tubular rotor, wherein the helical screw blade is secured to the inner surface of the tubular rotor. An advantage of the apparatus according to the invention is the relatively large cross-sectional area of the rotor interior through which the fluid to be compressed will pass. In addition there is no movement of the helical screw blade relative to the rotor so that the apparatus is less susceptible to wear at the high fluid flow rates which are encountered as gas is compressed. SPE paper 8245, Field testing the turbo-lift production system, by H. Petrie and J.W. Erickson, 1979, discloses a liquid powered downhole liquid pump comprising an open-ended housing and a solid rotor arranged rotatably in the housing. Both the liquid powered motor and the pump are staged turbines with blades arranged in the annular space between the housing and the solid rotor. The publication does not disclose an apparatus for compressing a fluid including a compressor arranged in a tubular rotor. The invention will now be described by way of example in more detail with reference to the accompanying drawings, wherein Figure 1 shows schematically a partial longitudinal section of the apparatus according to the invention; and Figure 2 shows schematically a partial longitudinal section of the lower end of a borehole provided with apparatus according to the invention, Figure 2 is drawn to a different scale. The apparatus 1 for compressing a fluid comprises a tubular, open-ended housing 2 having a suction end 5 and a discharge end 6. In the housing 2 is rotatably arranged a tubular, open-ended rotor 8. In Figure 1 is shown a sectional view of the part of the tubular rotor 8 near the suction end 5 and a side view of the rotor part near the discharge end 6. The tubular rotor 8 is supported in the housing 2 by a radial bearing 10 and by a bearing device 12. Bearing device 12 is a combination of a radial bearing, an axial bearing and a seal. The bearing device 12 is secured in the housing by bushing 15 which itself is secured in the housing by means of conventional fastening devices (not shown). The inner surface 16 of the bushing 12 is part of the inner surface of the housing 2. The apparatus further comprises an annular driver space 17 which is defined between the inner surface 16 of the housing 2 and the outer surface 18 of the tubular rotor 8. The annular driver space 17 is in fluid communication with the discharge end 6 of the housing 2. The bearing device 12 prevents fluid flow from the annular driver space 17 to the suction end 5. A rotor driver in the form of fluid powered motor 20 is arranged in the annular driving space 17. The fluid powered motor 20 comprises a plurality of curved strips 25 of similar shape secured to the outer surface of the tubular rotor 8. The spacing of adjacent strips 25 is substantially the same. The annular driving space 17 is provided with a power fluid inlet 26 debouching into the annular driver space 17 upstream to the fluid powered motor 20. The shape of the curved strips 25 is so selected that during normal operation a fluid flowing through the annular driver space 17 causes the rotor 8 to rotate. The apparatus further comprises a rotor-driven compressor 30 arranged in the tubular rotor 8. The compressor 30 includes a helical screw blade 32 which is secured to the inner surface 35 of the tubular rotor 8. To effect compression of gas the pitch of the helical screw blade 32 decreases in the direction of the discharge end 6. The shape of the helical screw blade 32 is so selected that during normal operation the pressure along the helical screw blade of the fluid increases from the level at the suction end to the desired level at the discharge end of the apparatus. The outer surface of the housing 2 is provided with a tapered section 37. Tapered section 37 can mate with a corresponding tapered section 40 (see Figure 2) of the lower end of a tubing 43. The tubing 43 is arranged in casing 47 which has been arranged in borehole 48 drilled towards reservoir 50. The tubing 43 is provided with apertures 53 which allow fluid communication from the annular space 55 between the casing 47 and the tubing 43 into the annular driver space 17 (see Figure 1) via the power fluid inlet 26. To prevent fluid communication between the annular space 55 and the suction end 5 of the housing of the apparatus 1, a packer 56 is provided at the lower end of the tubing 43 to seal the annular space 55. During normal operation, fluid flowing out of the reservoir 50 enters through the suction end 5 into the compressor 30. Driving fluid is supplied through the annular space 55 to the apertures 53 and 26 (see Figure 1) into the annular driver space 17. The driving fluid powers motor 20 which in its turn drives the tubular rotor 8. Fluid collected in the lower part of the borehole 48, under the packer 56 is sucked into the suction end 5 of the apparatus 1 by the action of the rotating compressor. Fluid passes through the interior of the tubular rotor 8 towards the outlet end 6 where it is joint by driving fluid leaving the annular driver space 17. The mixture of compressed fluid and driver fluid flows through the tubing 43 to surface. The number of turns per metre of the helical screw blade 32 of the compressor 30 is between 5 and 50. In the embodiment as described with reference to Figure 1 the rotor driver comprises a plurality of similar curved strips which are secured to the outer surface of the rotor. Alternatively the rotor driver includes a helical screw blade which is secured to the outer surface of the rotor. The number of turns per meter of the helical screw blade of the rotor driver is suitably between 4 and 48, and the number of helical screw blades is between two and four. In an alternative embodiment of the invention the rotor driver is an electric motor. In this case permanent magnets are secured to the rotor and suitable magnetic coils are arranged along the inner surface of the housing. The magnetic coils are powered via electric conduits extending to an electric power supply.

Claims: Apparatus (1) for compressing a fluid comprising a tubular, open-ended housing (2) having a suction end (5) and a discharge end (6), and a rotor-driven compressor (30) including a helical screw blade (32), wherein the pitch of the helical screw blade (32) decreases in the direction of the discharge end (6), characterized in that the apparatus (1) further comprises a tubular, open-ended rotor (8) rotatably arranged in the housing (2), an annular driver space (17) which is defined between the inner surface of the housing (2) and the outer surface of the rotor (8), an annular seal (12) preventing fluid flow from the annular driver space (17) to the suction end (5), and a rotor driver (20) arranged in the annular driver space (17), and in that the rotor-driven compressor (30) is arranged in the tubular rotor (8), wherein the helical screw blade (32) is secured to the inner surface of the tubular rotor (8). Apparatus according to claim 1, wherein the rotor driver (20) is an electric motor. Apparatus according to claim 1, wherein the rotor driver (20) is a fluid powered motor (20) arranged in the annular driver space (17) which is in fluid communication with the discharge end (6) and which is provided with a power fluid inlet (26) debouching into the annular driver space (17) up stream to the fluid powered motor (20). Apparatus as claimed in claim 3, wherein the fluid powered motor (20) comprises a plurality of similar curved strips (25) which are secured to the outer surface of the rotor (8) so that the spacing between adjacent strips (25) is substantially the same. Apparatus according to claim 3, wherein the fluid powered motor (20) includes a helical screw blade which is secured to the outer surface of the rotor (8).

Inventors: HEIJNEN, WILHELMUS HUBERTUS PAULUS MARIA
Applicants: SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1991
Main classification: E21B43
IPC codes: F04D13, F04D3, E21B43, F04D31