Adaptive pump control for positive displacement pump failure modes

1. A method, comprising:

detecting a failure mode of a fluid flow controller configured to control fluid flow between first and second chambers of a downhole positive displacement pump and a flow line, wherein the positive displacement pump comprises a piston moving in an axial reciprocating motion; and

adjusting operation of the downhole positive displacement pump based on the detected failure mode such that the downhole positive displacement pump piston operates differently in different axial directions.

2. The method of claim 1 wherein the failure mode of the downhole positive displacement pump results in a change in the amount of volume of fluid produced and/or injected by the downhole positive displacement pump corresponding to one stroke of the piston.

3. The method of claim 1 wherein the failure mode comprises an inactive stroke of a chamber of the downhole positive displacement pump, in which fluid:

does not enter the chamber; or

enters the chamber from an inadvertent source.

4. The method of claim 3 wherein adjusting operation of the downhole positive displacement pump comprises increasing an operating rate of the positive displacement pump for the inactive stroke.

5. The method of claim 1 wherein the axial reciprocating motion of the downhole positive displacement pump comprises:

a first stroke during which a first volume of fluid accumulates in a first pump chamber; and

a second stroke in a reverse direction from the first stroke during which a second volume of fluid accumulates in a second pump chamber.

6. The method of claim 5 wherein the piston moves at an essentially constant speed during one of the first and second strokes.

7. The method of claim 5 wherein adjusting operation of the downhole positive displacement pump comprises operating the positive displacement pump during the first stroke differently from during the second stroke.

8. The method of claim 5 wherein adjusting operation of the downhole positive displacement pump comprises increasing a stroke speed of the piston during one of the first and second strokes.

9. The method of claim 1 wherein detecting the failure mode comprises monitoring, using a microprocessor located downhole, a plurality of downhole sensors and downhole tool parameters.

10. The method of claim 1 wherein detecting the failure mode comprises:

measuring a pressure response to producing fluid from a subterranean formation during strokes of axially-opposite directions; and

observing a pressure pattern in the pressure response of the strokes of axially-opposite directions.

11. The method of claim 1 wherein detecting the failure mode comprises:

measuring a pressure response to producing fluid from a subterranean formation during strokes of axially-opposite directions; and

observing a difference between pressure drops during the strokes of axially-opposite directions.

12. The method of claim 1 wherein adjusting operation of the downhole positive displacement pump comprises adjusting operation of the downhole positive displacement pump automatically in response to receipt of at least one command from a surface tool by a microprocessor that is located downhole and is configured to control operation of the downhole positive displacement pump.

13. The method of claim 1 further comprising:

detecting repair of the failure mode of the flow controller; and

reversing the operation adjustment in response to the detected repair to essentially restore identical operation of the positive displacement pump during strokes of axially-opposite directions.

14. The method of claim 1 wherein the flow controller comprises a network of check valves, and wherein the failure mode comprises at least one check valve being clogged in an open position.

15. The method of claim 1 wherein:

operation of the downhole positive displacement pump produces fluid from or injects fluid into a subterranean formation via the flow line; and

adjusting operation of the downhole positive displacement pump is performed while maintaining fluid communication between the flow line and the subterranean formation.

16. The method of claim 1 wherein:

the failure mode comprises excessive sand accumulation in at least one chamber of the positive displacement pump; and

adjusting operation comprises reducing a length of strokes in one of the first and second chambers.

17. The method of claim 1 further comprising conveying an apparatus, via wireline or drill string, in a borehole extending into a subterranean formation, wherein the apparatus comprises the fluid flow controller, the downhole positive displacement pump, and the flow line.

18. A method, comprising:

detecting a clogging of a fluid flow controller in a downhole positive displacement pump that is in a failure mode as a result of being clogged in an open position; and

unclogging the fluid flow controller by adjusting an operating rate of the positive displacement pump so that the operating rate of a first stroke of the positive displacement pump is different from the operating rate of a second stroke of the positive displacement pump, resulting in passing fluid through the fluid flow controller at an increased speed, wherein:

in the failure mode, the first stroke corresponds to fluid flowing from a flow line through the fluid flow controller into a first chamber of the downhole positive displacement pump; and

in the failure mode, the second stroke corresponds to:

fluid not flowing from the flow line through the flow controller into a second chamber of the positive displacement pump; or

fluid flowing into the second chamber from an inadvertent source.

19. The method of claim 18 wherein the adjusted operating rate of the downhole positive displacement pump for the second stroke is faster than for the first stroke.

20. The method of claim 18 further comprising:

detecting an unclogging of the flow controller; and

restoring the initial operating rate of the positive displacement pump for the second stroke upon detection of the unclogging of the fluid flow controller.