Preconditioning flow to an electrical submersible pump

Abstract

A system and method of producing fluid from a wellbore by pressurizing the fluid and then directing the pressurized fluid to a centrifugal pump. Pressurizing the fluid compresses gas or vapor within the fluid, thereby decreasing the volume ratio of the gas or vapor within the fluid, which in turn increases operating efficiency of the centrifugal pump. A positive displacement pump, such as a gerotor pump, is used for pressurizing the fluid prior to sending it to the centrifugal pump.

What is claimed is: 
     
         1 . An electrical submersible pumping (“ESP”) system disposable in a wellbore comprising:
 a gerotor pump having,
 an inlet in communication with fluid in the wellbore, and 
 an exit through which fluid pressurized in the gerotor pump is directed away from the gerotor pump; 
 
 a centrifugal pump having,
 an inlet in fluid communication with the exit of the gerotor pump, and 
 a discharge in which fluid pressurized in the centrifugal pump is directed away from the centrifugal pump; and 
 
 production tubing in fluid communication with the discharge of the centrifugal pump. 
 
     
     
         2 . The ESP system of  claim 1 , wherein the gerotor pump comprises
 a body,   an idler in the body having an axis, planar upper and lower surfaces, a curved outer side surface, and a chamber having profiled sidewalls that lobes at designated locations along a circumference of the chamber, and   a rotor disposed in the chamber and having an axis, an outer circumference profiled to define gears that project radially outward, so that when the rotor is rotated about its axis, the gears contact the sidewall of the chamber at various locations to define sealing interfaces and define high and low pressure sides in the chamber.   
     
     
         3 . The ESP system of  claim 2 , wherein the rotor comprises n gears, and the idler comprises n+1 lobes. 
     
     
         4 . The ESP system of  claim 1 , wherein the centrifugal pump comprises a series of diffusers, impellers disposed between adjacent diffusers, and a flow path extending through the diffusers and impellers, so that when the impellers are rotated, fluid is urged through the flow path and is pressurized with distance through the flow path. 
     
     
         5 . The ESP system of  claim 1 , wherein an end of the production tubing distal from the centrifugal pump couples with a wellhead assembly disposed at an opening of the wellbore. 
     
     
         6 . The ESP system of  claim 1 , wherein the fluid being pressurized by the gerotor pump comprises a fluid having phases of liquid and gas or vapor. 
     
     
         7 . The ESP system of  claim 1 , further comprising a motor section mechanically coupled with the gerotor pump and the centrifugal pump, a seal section in pressure communication with the motor so that a pressure in the motor section remains at substantially ambient pressure, and a monitoring sub coupled with the motor section. 
     
     
         8 . The ESP system of  claim 1 , wherein the centrifugal pump operates at an increased efficiency when pressurizing fluid from the discharge of the gerotor pump than when pressurizing fluid received from the wellbore. 
     
     
         9 . An electrical submersible pumping (“ESP”) system disposable in a wellbore comprising:
 a positive displacement pump with a suction port in communication with fluid in the wellbore, a pressurization chamber in communication with the inlet, and a discharge port in communication with the pressurization chamber and that is at a pressure that is greater than a pressure of the suction port of the positive displacement pump; and 
 a centrifugal pump having a suction port in communication with the discharge of the positive displacement pump and a discharge port that is at a pressure greater than a pressure of the suction port of the centrifugal pump. 
 
     
     
         10 . The ESP system of  claim 9 , further comprising production tubing having an end in communication with the discharge port of the centrifugal pump and a distal end coupled to a wellhead assembly disposed at an opening of the wellbore. 
     
     
         11 . The ESP system of  claim 9 , wherein the positive displacement pump comprises a gerotor pump. 
     
     
         12 . The ESP system of  claim 9 , further comprising a motor mechanically coupled to the positive displacement pump and to the centrifugal pump, and a seal section in pressure communication with the motor, so that pressure in the motor is maintained substantially at ambient pressure when the motor is in the wellbore. 
     
     
         13 . The ESP system of  claim 9 , wherein when fluid in the wellbore comprises liquid and vapor or gas, a ratio of vapor or gas volume to liquid volume of the fluid is greater at the suction port of the positive displacement pump that at the suction port of the centrifugal pump, thereby increasing the operating efficiency of the centrifugal pump. 
     
     
         14 . A method of pumping fluid produced from within a wellbore comprising:
 pressurizing an amount of the fluid having phases of liquid and gas or vapor, so that the gas or vapor in the fluid is compressed to thereby reduce a ratio of gas or vapor volume to liquid volume;   directing the pressurized amount of the fluid to a centrifugal pump; and   further pressurizing the pressurized amount of the fluid with the centrifugal pump.   
     
     
         15 . The method of  claim 14 , wherein the step of pressurizing the amount of fluid having phases of liquid and gas or vapor is performed using a positive displacement pump. 
     
     
         16 . The method of  claim 15 , wherein the positive displacement pump comprises a gerotor pump. 
     
     
         17 . The method of  claim 14 , further comprising directing the fluid further pressurized by the centrifugal pump to a wellhead assembly disposed at an opening of the wellbore. 
     
     
         18 . The method of  claim 15 , further comprising powering both the positive displacement pump and the centrifugal pump with a single motor.