Pressure limiter for a downhole pump and testing apparatus

• US 4,729,430 A
• Filed: 10/27/1986
• Issued: 03/08/1988
• Est. Priority Date: 10/27/1986
• Status: Expired due to Fees

• Current Assignee: Halliburton Company
• Original Assignee: Halliburton Company
• Inventors: White, Kevin M., Ringgenberg, Paul D.
• Primary Examiner(s): Novosad, Stephen J.
• Assistant Examiner(s): Neuder, William P.
• Application Number:
  US06/923,800
• Time in Patent Office: 498 Days
• Field of Search: 166/250, 166/68, 166/105, 166/106, 166/187, 166/191, 166/127, 166/130, 166/183, 417/395, 415/26
• US Class Current: 166/106
• CPC Class Codes: E21B 33/1246 inflated by down-hole pumping means operated by a pipe string
• CPC Class Codes: E21B 33/1272 inflated by down-hole pumping means operated by a pipe string
• CPC Class Codes: F04B 43/067 the fluid being actuated directly by a piston

Abstract

A pressure limiter and pump for use in a testing string. The pressure limiter has an outer case and an inner mandrel which form an enclosure defining an annulus therebetween. The inlet and outlet check valves in the annulus define a pumping chamber therebetween which opens toward the pump. Fluid in the pumping chamber is never vented to the well annulus. In a first embodiment, a transversely mounted pressure limiter piston provides communication between the pumping chamber and a lower portion of the testing string when actuated. In the second and third embodiments, a pressure limiter piston is reciprocably disposed in the annulus between the case and mandrel; at a predetermined pressure differential, the pressure limiter piston reciprocates such that the volume in the pumping chamber is increased. A fourth embodiment simply uses a pumping chamber of predetermined volume such that the efficiency of the pump drops to essentially zero when the pressure in the pumping chamber reaches a predetermined level; no pressure limiter piston is used.

Claims

1. A pressure limiter apparatus for use in a well testing string having a positive displacement pump including a fluid displacement element, said apparatus comprising:

enclosure means in said well testing string having a wall defining a pumping chamber adjacent said pump and in pressure transmitting communication with said fluid displacement element;

inlet valve means associated with said enclosure means for controlling flow of fluid from a well annulus into said pumping chamber;

outlet valve means associated with said enclosure means for controlling flow of fluid from said pumping chamber to a lower well testing string portion; and

pressure limiting means in communication with said pumping chamber for increasing the volume of said pumping chamber when a positive fluid pressure differential between said pumping chamber and said well annulus exceeds a predetermined value and for preventing venting of said fluid in said pumping chamber to said well annulus when said volume is so increased.

2. The apparatus of claim 1 wherein said pressure limiting means is disposed substantially between said inlet and outlet valve means.

3. The apparatus of claim 1 wherein said enclosure means further includes a hole through the wall thereof providing communication between said pumping chamber and said lower testing string portion through bypass passage means defining a flow path bypassing said outlet valve means and said pressure limiter means comprises:

a piston sealingly closing said hole to said bypass passage means when in a normal operating position and opening said hole to said bypass passage means when in an actuated position such that said pumping chamber and said lower testing string portion are in communication; and

biasing means for biasing said piston toward said normal operating position.

4. The apparatus of claim 1 wherein said pressure limiting means comprises:

piston means reciprocably disposed in said enclosure means and having a first portion and a second portion relatively smaller than said first portion such that an annular area is defined between said first and second portions, said piston means being movable in response to pumping action of said pump such that said volume of said pumping chamber is increased by an amount approximately equal to a displacement of said pump;

first sealing means for sealingly separating said pumping chamber and said well annulus adjacent said first portion of said piston means; and

second sealing means for sealingly separating said pumping chamber from said well annulus adjacent said second portion of said piston means.

5. The apparatus of claim 4 further comprising biasing means for biasing said piston means toward a position minimizing said volume of said pumping chamber.

6. The apparatus of claim 4 wherein:

said piston means includes a third portion relatively smaller than said second portion such that another annular area is defined between said second and third portions in communication with said lower testing string portion;

said second sealing means is further adapted for sealingly separating said well annulus and said lower testing string portion; and

said pressure limiting means further comprises third sealing means for sealingly separating said pumping chamber and said lower testing string portion adjacent said third portion of said piston means.

7. The apparatus of claim 4 wherein said inlet valve means is mounted on said piston means.

8. The apparatus of claim 7 further comprising filtering means on said piston means for filtering said fluid in said well annulus flowing to said inlet valve means.

9. A pressure limiting apparatus comprising:

a case having an upper end adapted for attachment to a pump in an upper testing string portion and a lower end adapted for attachment to a lower testing string portion, said case defining a transverse hole therethrough between said upper and lower ends;

an inner mandrel having an upper end adapted for attachment to a mandrel in said upper testing string portion and a lower end adapted for attachment to a mandrel in said lower testing string portion, said case and mandrel defining an annulus therebetween;

an inlet check valve disposed in said annulus and defining an inlet chamber portion of said annulus in communication with said hole in said case;

an outlet check valve disposed in said annulus and defining an outlet chamber portion of said annulus in communication with said lower testing string portion, said inlet and outlet check valves defining a pumping chamber portion of said annulus therebetween, said pumping chamber opening adjacent said pump;

a piston reciprocably disposed in said annulus between a normal position and an actuated position, said piston comprising;

a first cylindrical portion; and

a second cylindrical portion relatively smaller than said first cylindrical portion such that an annulus area is defined therebetween, said annular area being exposed to well hydrostatic pressure in said inlet chamber on an outer side of said piston and exposed to pumping chamber pressure on an inner side of said piston; and

biasing means for biasing said piston toward said normal position;

wherein, said piston is moved from said normal position to said actuated position when a differential pressure level between said pumping chamber and said inlet chamber acting on said annular area overcomes a force exerted by said biasing means, movement of said piston increasing a volume of said pumping chamber by an amount approximately equal to a displacement of a pump in said upper testing string portion such that said outlet check valve is rendered inoperative.

10. The apparatus of claim 9 wherein said inlet check valve is mounted on said piston.

11. The apparatus of claim 9 further comprising:

first sealing means for sealing on said first cylindrical portion of said piston between said pumping chamber and said inlet chamber; and

second sealing means for sealing on said second cylindrical portion of said piston between said pumping chamber and said inlet chamber.

12. The apparatus of claim 9 wherein:

said case has a shoulder thereon in said inlet chamber;

said piston has a shoulder thereon in said inlet chamber and generally facing said shoulder on said case; and

said biasing means is characterized by at least one spring annularly positioned in said inlet chamber between said shoulders.

13. The apparatus of claim 12 further comprising a plurality of spacers between said spring and at least one of said shoulders for selectively increasing a preload of said spring.

14. The apparatus of claim 9 further comprising an inlet screen mounted on said piston for filtering fluid flowing from said inlet chamber to said inlet check valve.

15. The apparatus of claim 9 wherein said piston further includes a third cylindrical portion relatively smaller than said second cylindrical portion thereof.

16. The apparatus of claim 15 further comprising:

first sealing means for sealing on said first cylindrical portion of said piston between said pumping chamber and said inlet chamber;

second sealing means for sealing on said second cylindrical portion of said piston between said inlet chamber and said inlet chamber; and

third sealing means for sealing on said third cylindrical portion of said piston between said pumping chamber and said outlet chamber.

17. The apparatus of claim 9 wherein:

said inlet check valve comprises a resilient valve portion having an annular lip thereon sealingly engaged with a surface of said pumping chamber when in a closed position; and

said outlet check valve comprises a resilient valve portion having an annular lip thereon sealingly engaged with a surface of said pumping chamber when in a closed position.

18. A downhole testing tool for use on a testing string in a well annulus and having a central flow passageway therethrough, said tool comprising:

a tester valve;

a positive displacement pump positioned below said tester valve;

a packer disposed below said pump and positionable in said well annulus above a formation to be tested, said packer being inflatable by said pump into sealing engagement with said well annulus;

a pressure limiter between said pump and said packer for limiting pressure in said pump and packer and preventing overinflation of said packer, said pressure limiter defining a pumping chamber therein adjacent and in pressure transmitting communication with said pump and comprising;

an inlet valve for allowing fluid flow from said well annulus into said pumping chamber;

an outlet valve for allowing fluid flow from said pumping chamber to said packer; and

means for internally bypassing said outlet valve when a positive differential between pressure in said pump and pumping chamber and pressure in said well annulus adjacent thereto exceeds a predetermined level; and

a porting sub positionable adjacent said formation for allowing well fluid flow therethrough into said central flow passageway in response to actuation of said tester valve during a testing operation.

19. The testing tool of claim 18 wherein said fluid flows from said pumping chamber is continuously sealingly separated from said well annulus.

20. The testing tool of claim 18 wherein said means for bypassing is characterized by a reciprocable piston in said pumping chamber, said piston being movable such that said volume of said pumping chamber is increased by an amount approximately equal to a displacement of said pump.