ELECTRIC POWER GENERATOR FOR USE IN A WELLBORE

Abstract: An electric power generator for use in a wellbore for the production of a hydrocarbon gas stream from an earth formation, comprising a conduit having a fluid passage for the stream, and an electric circuit including a thermocouple having a primary thermocouple junction and a secondary thermocouple junction, wherein the primary thermocouple junction is arranged to be in thermal contact with the gas stream at a first location of the fluid passage and the secondary thermocouple junction is arranged to be in thermal contact with the gas stream at a second location of the gas stream, and wherein the flow area of the passage at the second location is larger than the flow area of the passage at the first location.

Description: ELECTRIC POWER GENERATOR FOR USE IN A WELLBORE The present invention relates to an electric power generator for use in a wellbore for the production of hydrocarbon gas stream from an earth formation. In the practice of exploitation of hydrocarbon gas from a subsurface reservoir via a wellbore, various operational parameters are to be controlled. A variety of electrically operated wellbore tools have been applied, either powered from surface via a conductor, or by means of a rechargeable downhole battery. Both applications have their own specific disadvantages. For example, a conductor to surface requires wet conductor connections which are vulnerable to malfunction. Downhole rechargeable batteries require rather complicated power generators to recharge the batteries. It is an object of the invention to provide an improved power generator which overcomes the drawbacks of the prior art. In accordance with the invention there is provided an electric power generator for use in a wellbore for the production of a hydrocarbon gas stream from an earth formation, comprising a conduit having a fluid passage for the stream, and an electric circuit including a thermocouple having a primary thermocouple junction and a secondary thermocouple junction, wherein the primary thermocouple junction is arranged to be in thermal contact with the gas stream at a first location of the fluid passage and the secondary thermocouple junction is arranged to be in thermal contact with the gas stream at a second location of the gas stream, and wherein the flow area of the passage at the second location is larger than the flow area of the passage at the first location. The temperature of the gas stream changes as the stream flows between the first and second locations by virtue of the change in flow area. For example, if the stream flows from the second to the first location the temperature increases by virtue of compression of the gas, or, if the stream flows from the first to the second location the temperature decreases by virtue of expansion of the gas . In this manner a temperature difference is created between the primary and secondary thermocouple junctions, resulting in an electric current in the circuit. Suitably said conduit forms part of a valve for controlling the flow rate of the stream of gas, the valve comprising a closure member arranged in the conduit and being movable relative to the flow restriction between an open position in which the flow restriction is open and a closed position in which the closure member closes the flow restriction. The invention will be described hereinafter in more detail and by way of example with reference to the accompanying drawings in which: Fig. 1 schematically shows a longitudinal cross- section of an embodiment of a downhole safety valve according to the invention; and Fig. 2 schematically shows a detail of the embodiment of Fig. 1. In Fig. 1 is shown a wellbore 1 formed into an earth formation 2 for the production of a stream of hydrocarbon gas. The wellbore 1 is provided with a casing 3 fixed in the wellbore by a layer of cement 4. A downhole safety valve 6 according to the invention is concentrically arranged in the casing 3 and fixed to the casing by a packer 8 which prevents hydrocarbon gas from bypassing the safety valve 6. The direction of flow of the gas is indicated by arrows 9. The safety valve 6 includes a conduit in the form of tubular valve body 10 having a plurality of gas inlets in the form of slots 12 (only one of which is shown) provided in the tubular valve body and a gas outlet 14 in fluid communication with the slots 12 via a flow restriction 16. A valve seat 17 extends around the flow restriction 16 at the upstream side thereof. A closure member 18 is arranged in the valve body 10, the closure member having a front surface 20 matching the valve seat 17. The closure member 18 is movable in axial direction of the valve body 10 between an open position (as shown in Fig. 1) in which the front surface 20 is located away from the valve seat 17 and a closed position in which the front surface 20 contacts the valve seat 17 and thereby closes the valve. A small radial clearance 22 is present between the outer surface of the closure member 18 and the inner surface of the valve body 10. A spiral tension spring 24 is provided in the tubular valve body 10, one end of the spring 24 being connected to the closure member 18, the other end to a stop member 26 arranged in the valve body. The stop member 26 is adjustable in axial direction of the valve body 10 in order to adjust the tension force of the spring 24. When in rest position, the spring 24 holds the closure member 18 in the open position thereof. The upstream end part of the valve body 10 is provided with an activating device in the form of a flapper valve 30 operable between a closed position in which flow of the stream of gas against the 18 closure member is substantially prevented, and an open position in which flow of the stream of gas into the valve body 10 and against the closure member 18 is allowed. The flapper valve 30 includes a flapper 32 arranged inside the tubular valve body 10 and being connected to a rotatable shaft 34 which divides the flapper 32 in portions of different surface areas. To illustrate this arrangement, the eccentricity between the rotatable shaft 34 and the longitudinal axis 36 of the tubular valve body 10 has been indicated by reference sign 38. Referring further to Fig. 2, the rotatable shaft 34 extends through a chamber 40 provided in the valve body 10. The shaft 34 has a cam surface arranged in the chamber 40 and formed by a flat surface portion 43 of the shaft, the flat surface portion 43 extending parallel to the flapper 32. The remaining surface portion of the axis 34 has a circular cross-section. The chamber 40 is provided with a solenoid assembly 42 including a solenoid coil 44, a spring (not shown) and a slideable shaft 46 movable relative to the solenoid coil between an extended position in which the shaft contacts the flat surface portion 43 of rotatable shaft 34 and a retracted position in which the slideable shaft 46 is retracted from the rotatable shaft 34. The solenoid coil 44, when activated, biases the shaft 46 to the extended position thereof. When the solenoid coil 44 is deactivated, the spring biases the shaft 46 to the retracted position thereof. The tubular valve body 10 is provided with a plurality of thermocouples 50 (only two of which are shown) arranged in an annular recess 52 provided at the outer surface of the valve body 10. Each thermocouple 50 has a positive lead 54 arranged at the upstream side of the flow restriction 16 and a negative lead 56 arranged at the downstream side of the flow restriction 16, the leads 54, 56 being in thermal contact with the tubular valve body 10 and being incorporated in an electric circuit (not shown) including a rechargeable battery for powering the solenoid assembly 42 and a control system for controlling the power supply from the battery to the solenoid assembly 42. The control system is arranged to supply power to the solenoid assembly 42 upon receipt of a continuous series of acoustic signals transmitted from surface through the casing to the control system. The control system switches off the power supply in the absence of said series of acoustic signals. The annular recess 52 is sealed from the exterior of the valve body 10 by an annular epoxy shield 58. The shaft 34 is furthermore provided connected to a spiral spring (not shown) which biases the shaft 34 to the position in which the flapper 32 is in the closed position thereof. During normal operation a stream of hydrocarbon gas produced from the earth formation flows at a normal flow rate through the casing 3 in the direction 9 to the safety valve 6. The flapper 32 is kept in its closed position by virtue of a continuous series of acoustic signals is supplied from surface via the casing 3 to the control system of the solenoid assembly 42 so that the battery continuously supplies power to the solenoid assembly 42 which thereby biases the slideable shaft 46 against flat surface portion of the shaft 34. As a result rotation of the flapper 32 to its open position is prevented. The flapper 32 prevents flow of the stream of gas into the valve body 10 and against the closure element 18, and the closure element 18 is kept in its open position by the action of the tension spring 24. The stream of gas flows via the slots 12 via the flow restriction 16 to the gas outlet 14. From the gas outlet 14 the gas flows further through the casing 3 in the direction 9 to a processing facility (not shown) at surface. As the stream flows through the flow restriction 16, the stream undergoes a temperature drop due to expansion of the stream upon leaving the flow restriction 16. The temperature drop leads to a temperature difference in the valve body 10 between the locations of the respective positive leads 54 and the negative leads 56. The leads 54, 56 are subjected to the same temperature difference by virtue of their thermal contact with the valve body 10. As a result an electric current is generated in each thermocouple, which current flows via the electric circuit to the battery and thereby charges the battery. When it is desired to close the safety valve 6, transmission of the acoustic signals is stopped. The control system thereby switches off the power supply to the solenoid assembly 42 so that the spring biases the slideable shaft 46 to the retracted position thereof. Rotation of the axis 34 is then no longer counter-acted by slideable shaft 46, and the flow of the stream against the flapper 32 induces a turning moment to the flapper 32 causing the flapper 32 to rotate to its open position. With the flapper 32 in its open position, the stream is allowed to flow into the valve body 10 and against the closure member 18. As a result the closure member 18 becomes subjected to a drag force which causes the closure member 18 to move to the closed position thereof against the action of the spring 24 and thereby to close the safety valve 6.

Claims: C L I M S 1. An electric power generator for use in a wellbore for the production of a hydrocarbon gas stream from an earth formation, comprising a conduit having a fluid passage for the stream, and an electric circuit including a thermocouple having a primary thermocouple junction and a secondary thermocouple junction, wherein the primary thermocouple junction is arranged to be in thermal contact with the gas stream at a first location of the fluid passage and the secondary thermocouple junction is arranged to be in thermal contact with the gas stream at a second location of the gas stream, and wherein the flow area of the passage at the second location is larger than the flow area of the passage at the first location. 2. The electric power generator of claim 1, wherein the difference between the flow areas of the passage at the first and second locations thereof is defined by a flow restriction provided in the fluid passage. 3. The electric power generator of claim 2, wherein the flow restriction includes a section of diverging diameter in downstream direction of the gas stream, and wherein the primary thermocouple junction is arranged to be in thermal contact with the gas stream upstream the section of diverging diameter and the secondary thermocouple junction is arranged to be in thermal contact with the gas stream downstream the section of diverging diameter. 4. The electric power generator of any one of claims 1-3, wherein said conduit forms part of a valve for controlling the flow rate of the stream of gas, the valve comprising a closure member arranged in the conduit and being movable relative to the flow restriction between an open position in which the flow restriction is open and a closed position in which the closure member closes the flow restriction. 5. The electric power generator of claim 4, wherein the valve further comprises an activating device for selectively subjecting the closure member to a drag force of selected magnitude, the drag force being exerted by the stream of fluid and inducing the closure member to move from the open position to the closed position thereof, and an electric control system for controlling the activating device so as to subject the closure member to said drag force, and wherein said thermocouple is arranged to provide electric power to the control system. 6. The electric power generator of claim 5, wherein the activating device is operable between a first mode in which flow of the stream of fluid against the closure member is substantially prevented, and a second mode in which flow of the stream of fluid against the closure member is allowed. 7. The electric power generator of claim 6, wherein in said first mode the activating device substantially prevents flow of the stream of fluid into the conduit, and in said second mode the activating device allows flow of the stream of fluid into the conduit. 8. The electric power generator of any one of claims 5-7, wherein the activating device includes a flapper valve having a flapper arranged upstream the closure member, the flapper being rotatable between a closed position in which the flapper substantially closes the conduit and an open position in which the flapper substantially leaves the conduit open. 9. The electric power generator of claim 8, wherein the flapper is rotatable about an axis dividing the flapper in portions of different surface areas, and wherein the electric control system includes a solenoid assembly operable between an activated mode in which rotation of the flapper is prevented and a deactivated mode in which rotation of the flapper is allowed. 10. The electric power generator of claim 9, wherein the flapper is fixed to a rotatable shaft including a cam surface, and wherein the assembly is biased against the rotatable shaft when in the activated mode. 11. The electric power generator of claim 10, wherein the cam surface includes a substantially flat surface portion of the shaft. 12. The electric power generator substantially as described hereinbefore with reference to the drawings.

Inventors: HEIJNEN WILHELMUS HUBERTUS PAU, OUDEMAN PIETER, ZIJSLING DJURRE HANS, HEIJNEN, WILHELMUS, HUBERTUS, PAULUS, MARIA, OUDEMAN, PIETER, ZIJSLING, DJURRE, HANS
Applicants: HEIJNEN WILHELMUS HUBERTUS PAU, OUDEMAN PIETER, SHELL INT RESEARCH, ZIJSLING DJURRE HANS, HEIJNEN, WILHELMUS, HUBERTUS, PAULUS, MARIA, OUDEMAN, PIETER, SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V., ZIJSLING, DJURRE, HANS
Application year: 2000
Main classification: E21B41
IPC codes: E21B41, H01L35