Fluid pumping using electric linear motor

Abstract

A drilling fluid pump system includes a plurality of modular pump units that are each driven by a linear electric motor. A control system that can include positional feedback information which is used to control all of the linear motors in the pump system and reduce pressure pulsation. The linear motors can be controlled to reduce fluid pressure pulsation by controlling velocity and relative timing between pistons. To accommodate removal and addition of individual pump units the pump modules can be isolated electrically and hydraulically. This can improve scalability, reliability, and serviceability of the pump system.

What is claimed is: 
     
         1 . A pump system configured to pump fluid down a wellbore, the system comprising:
 an electrically-powered linear motor including a stationary portion and a moving portion, the moving portion adapted to move in a reciprocating fashion relative to the stationary portion; and   a pump assembly including a piston and one or more valves configured to pump a fluid into a wellbore, the piston being driven by the reciprocating moving portion.   
     
     
         2 . A pump system according to  claim 1  further comprising:
 a sensor configured to detect movement and/or position of at least a portion of the motor and/or pump assembly and output position information; and 
 a control system configured to control the motion of linear motor, to receive the position information and to make adjustments the control based at least in part on the position information thereby reducing error in said motion. 
 
     
     
         3 . A pump system according to  claim 2  wherein said control system is further configured to reducing flow pulsation of fluid pumped by the pump system based at least in part on said position information. 
     
     
         4 . A pump system according to  claim 3  further comprising a pressure sensor configured to detect discharge fluid pressure of the pump system and output pressure information, and said reducing flow pulsation of fluid pumped by the pump system is further based at least in part on said pressure information. 
     
     
         5 . A pump system according to  claim 2  said motor and said pump assembly together form a pump unit, and said system further comprising one or more additional pump units, each of which includes at least one linear motor and at least one pump assembly, and wherein said control system is further configured to adjust relative timing of each motor based on a total number of pump units in the pump system. 
     
     
         6 . A pump system according to  claim 1  wherein the moving portion is rod-shaped and the stationary portion is tube-shaped and surrounds the rod-shaped moving portion. 
     
     
         7 . A pump system according to  claim 6  wherein the rod-shaped moving portion is vertically oriented and is configured to move in a vertical direction. 
     
     
         8 . A pump system according to  claim 1  wherein the moving portions and the stationary portions are rectangular and planar in shape, and the stationary portion includes two planar portions disposed on either side of and sandwiching the moving portion. 
     
     
         9 . A pump system according to  claim 8  wherein the moving portion is configured to move primarily in horizontal direction. 
     
     
         10 . A pump system according to  claim 1  further comprising a second pump assembly including a second piston and a set of second valves configured to pump the fluid into the wellbore, the second piston being driven by said reciprocating moving portion. 
     
     
         11 . A pump system according to  claim 10  further comprising a plurality of isolation valves positioned and configured to hydraulically isolate either of said pump assembly or said second pump assembly thereby facilitating servicing and/or replacement of pump system components without loss of pump system operation. 
     
     
         12 . A pump system according to  claim 1  wherein said fluid is selected from a group consisting of: drilling mud, circulation fluid, and fracturing fluid. 
     
     
         13 . A method of pumping a fluid into a wellbore comprising:
 controlling a first electrically-powered linear motor that includes a stationary portion and a moving portion, such that the moving portion moves in a reciprocating fashion relative to the stationary portion and drives a first pump assembly that includes a piston and one or more valves, thereby causing a fluid to flow into the wellbore;   receiving position information from a sensor configured to detect movement and/or position of at least a portion of the motor and/or pump assembly; and   adjusting said controlling based at least in part on the position information thereby reducing error in said controlling.   
     
     
         14 . A method according  claim 13  wherein said first motor and said first pump assembly together form a first pump unit, and said controlling includes controlling a plurality of additional pump units, said first pump unit and said additional pump units forming a pump system. 
     
     
         15 . A method according to  claim 14  further comprising:
 altering the number of pump units being controlled; and 
 adjusting relative timing of each motor based on a new total number of pump units in the pump system. 
 
     
     
         16 . A method according to  claim 14  further comprising receiving pressure information from a sensor configured to detect pressure of the fluid being discharged from said pump system, and said controlling further includes controlling said first pump unit and said plurality of additional pump units to reduce pressure pulsations bases at least in part on information from said pressure sensor. 
     
     
         17 . A method according to  claim 16  wherein said reducing pressure pulsations is achieved at least in part by controlling piston velocity profiles of each pump unit and phase angles between the pump units. 
     
     
         18 . A method according to  claim 13  wherein the pump said moving portion of the first electrically-powered linear motor further drives a second pump assembly including a second piston and a set of second valves configured to pump the fluid into the wellbore. 
     
     
         19 . A method according to  claim 13  wherein said fluid is selected from a group consisting of: drilling mud, circulation fluid, and fracturing fluid.