Well service pump systems and related methods

Abstract

A well service pump system supplies high pressure working fluid to a well. The pump system includes a closed-loop hydraulic circuit for actuating a plurality of working pump assemblies. The pump system is powered by a motor, which transfers mechanical energy to a plurality of pumps, which, in turn, provide hydraulic fluid to operate hydraulic ram cylinders, and thereby operate the working pump assemblies. Each of the polished rods of the hydraulic ram cylinders is connected axially to a plunger rod end of the working fluid end cylinder to operate the working pump assembly.

1 . A well service pump system for delivering working fluid at high pressure to a well, the pump system comprising:
 at least two working fluid pump assemblies, each comprising:
 a working fluid end cylinder having a plunger rod configured to reciprocate within the fluid end cylinder; and 
 a hydraulic ram cylinder having a ram piston configured to reciprocate within the ram cylinder and a piston rod coupled to the ram piston and coupled to the plunger rod of the working fluid end cylinder such that the ram piston of the hydraulic ram cylinder can be actuated to move the plunger rod of the working fluid end cylinder:
 in a first direction to expel working fluid from the fluid end cylinder during a forward stroke of the plunger rod, and 
 in a second direction to draw working fluid into the fluid end cylinder during a return stroke of the plunger rod; 
 
 wherein the hydraulic ram cylinder includes a first hydraulic port on a first side of the ram piston and a second hydraulic port on a second side of the ram piston; 
   a plurality of bi-directional pumps, each coupled to a respective one of the working fluid pump assemblies such that the bi-directional pump is in fluid communication with the first hydraulic port and the second hydraulic port of the hydraulic ram cylinder to pump hydraulic fluid:
 from the second hydraulic port directly into the first hydraulic port to actuate the ram piston to drive the plunger rod in the first direction; and 
 from the first hydraulic port directly into the second hydraulic port to actuate the ram piston to drive the plunger rod in the second direction. 
   
     
     
         2 . The well service pump system of  claim 1 , comprising a fluid reservoir configured to be in fluid communication with each of the plurality of bi-directional pumps to compensate for leakage in the system. 
     
     
         3 . The well service pump system of  claim 1 , wherein, when the ram piston of the hydraulic ram cylinder reciprocates within the hydraulic ram cylinder, the ram piston is, at all times, spaced a distance from a first end wall of the hydraulic ram cylinder and a second end wall of the hydraulic ram cylinder opposite the first end wall. 
     
     
         4 . The well service pump system of  claim 1 , comprising a motor configured to drive each of the bi-directional pumps to direct fluid to the first and second ports. 
     
     
         5 . The well service pump system of  claim 4 , comprising a pump drive coupled to the motor and to each of the bi-directional pumps, the pump drive configured to transfer mechanical energy from the motor to each of the bi-directional pumps. 
     
     
         6 . The well service pump system of  claim 5 , wherein at least one of the bi-directional pumps is mounted to the pump drive. 
     
     
         7 . The well service pump system of  claim 4 , wherein the motor comprises an electric motor. 
     
     
         8 . The well service pump system of  claim 1 , wherein, for at least one of the working fluid pump assemblies, the ram piston has an actuatable piston surface area that is at least two times greater than an actuatable piston surface area of the plunger rod. 
     
     
         9 . The well service pump system of  claim 1 , wherein each working fluid pump assembly further comprises a coupling member coupled to the plunger rod of the working fluid end cylinder and to the piston rod of the hydraulic ram cylinder. 
     
     
         10 . The well service pump system of  claim 1 , wherein in each working fluid pump assembly, the piston rod of the hydraulic ram cylinder is axially aligned with the plunger rod of the hydraulic ram cylinder. 
     
     
         11 . The well service pump system of  claim 1 , wherein in each working fluid pump assembly, the working fluid end cylinder has a cylindrical inner wall and the plunger rod has an outer surface that is spaced apart from the cylindrical inner wall such that the working fluid end cylinder can pump abrasive fluids without the plunger rod and the cylinder inner wall simultaneously contacting individual particles in the working fluid. 
     
     
         12 . The well service pump system of  claim 1 , wherein at least one of the hydraulic pumps comprises a fixed-displacement hydraulic pump. 
     
     
         13 . The well service pump system of  claim 1 , wherein each working fluid pump assembly further comprises:
 an inlet check valve coupled to the fluid end cylinder and configured to permit working fluid to be drawn into the fluid end cylinder but prevent working fluid from exiting the fluid end cylinder through the inlet check valve; and   an outlet check valve coupled to the fluid end cylinder and configured to permit working fluid to exit the fluid end cylinder while preventing working fluid from being drawn into the fluid end cylinder through the outlet check valve.   
     
     
         14 . The well service pump system of  claim 13 , wherein, for at least one of the working fluid pump assemblies, the working fluid is pressurized when it enters the fluid end cylinder through the inlet check valve. 
     
     
         15 . A method comprising:
 delivering a working fluid to a well with a well service pump system comprising:
 at least two working fluid pump assemblies, each comprising:
 a working fluid end cylinder having a plunger rod configured to reciprocate within the fluid end cylinder; and 
 a hydraulic ram cylinder having a ram piston configured to reciprocate within the hydraulic ram cylinder and a piston rod coupled to the ram piston and coupled to the plunger rod of the working fluid end cylinder; 
 wherein the hydraulic ram cylinder includes a first hydraulic port on a first side of the ram piston and second hydraulic port on a second side of the ram piston; 
 
 a plurality of bi-directional pumps, each fluidly coupled to a respective one of the working fluid pump assemblies; 
   wherein delivering the working fluid comprises:
 actuating the ram piston of the hydraulic ram cylinder to move the plunger rod of the working fluid end cylinder:
 in a first direction to expel working fluid from the fluid end cylinder during a forward stroke of the plunger rod, and 
 in a second direction to draw working fluid into the fluid end cylinder during a return stroke of the plunger rod; and 
 
 directing hydraulic fluid, via the bi-directional pump:
 from the second hydraulic port directly into the first hydraulic port to actuate the ram piston to drive the plunger rod in the first direction; and 
 from the first hydraulic port directly into the second hydraulic port to actuate the ram piston to drive the plunger rod in the second direction. 
 
   
     
     
         16 . The method of  claim 15 , comprising actuating a motor to drive each of the bi-directional pumps to direct fluid to the first and second ports. 
     
     
         17 . The method of  claim 16 , wherein the motor comprises an electric motor. 
     
     
         18 . The method of  claim 15 , wherein at least one of the hydraulic pumps comprises a fixed-displacement hydraulic pump. 
     
     
         19 . The well service pump system of  claim 4 , wherein the motor comprises a combustion engine. 
     
     
         20 . The method of  claim 16 , wherein the motor comprises a combustion engine.