Adaptive Pump Control For Positive Displacement Pump Failure Modes

Abstract

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 subsequently 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.

What is claimed is: 
     
         1 . An apparatus, comprising:
 a downhole tool conveyable within a wellbore that extends into a subterranean formation, wherein the downhole tool comprises:
 a pump comprising:
 a first chamber having a first inlet valve and a first outlet valve; 
 a second chamber having a second inlet valve and a second outlet valve; and 
 a piston having opposing first and second surfaces defining respective moveable boundaries of the first and second chambers; 
 
 at least one sensor operable to sense a first pressure in at least one of the first and second chambers; and 
 a controller operable to control the first and second inlet and outlet valves in coordination with movement of the piston to draw fluid from the subterranean formation and expel fluid into the wellbore, wherein such control of the first and second inlet and outlet valves is based at least in part on the sensed first pressure and a second pressure of fluid in at least one of the wellbore and the subterranean formation. 
   
     
     
         2 . The apparatus of  claim 1  wherein:
 the downhole tool further comprises a flow line; 
 the at least one sensor is operable to sense a pressure response to pumping fluid between the flow line and one of the first and second chambers; and 
 the controller is further operable to detect a failure mode of the pump based on the sensed pressure response. 
 
     
     
         3 . The apparatus of  claim 1  wherein:
 the downhole tool further comprises a sample chamber; and 
 the controller is further operable to control the first and second inlet and outlet valves in coordination with movement of the piston to pump fluid drawn from the subterranean formation into the sample chamber.