Downhole compressor for charging an electrical submersible pump

Abstract

Downhole Electric Submersible Pumps (ESP) in a production string often experience gas lock caused by free gas present in the production liquids which reduces the intake pressure below operating parameters of the ESP. A compressor is disclosed for compressing production fluid prior to feeding the production fluid into an ESP intake. The compression entrains or dissolves free gas into the production liquid, reducing the risk of gas lock of the ESP. The compression increases production fluid pressure to within the operating pressure of the ESP intake, to a selected pressure, or to above the free gas bubble point.

What is claimed is: 
     
         1 . A method of producing fluid from a subterranean well having a wellbore extending through a hydrocarbon-bearing formation, the method comprising the steps of:
 positioning at a downhole location in the wellbore a work string having an electric motor, a compressor assembly, and an Electric Submersible Pump (ESP);   operating the compressor assembly and the ESP using the electric motor;   pumping production fluid from the formation and into an interior passageway of the work string, the production fluid having both free gas and production liquid therein;   compressing the production fluid using the compressor assembly, and entraining or dissolving at least a portion of the free gas into the production liquid; and   feeding the compressed production fluid to an intake of the ESP.   
     
     
         2 . The method of  claim 1 , wherein the step of compressing further comprises compressing the production fluid to an intake pressure within the operating range of the ESP intake. 
     
     
         3 . The method of  claim 1 , wherein the step of compressing further comprises compressing the production fluid by between about 8 psi (55 kPa) and 60 psi (414 kPa). 
     
     
         4 . The method of  claim 1 , wherein the step of compressing further comprises compressing the production fluid to a pressure above the free gas bubble point at the downhole location. 
     
     
         5 . The method of  claim 1 , wherein the step of compressing further comprises compressing the production fluid in multiple stages in the compressor assembly, and wherein each of the multiple stages compresses the production fluid by between about 8 psi (55 kPa) and 32 psi (221 kPa). 
     
     
         6 . The method of  claim 1 , wherein the compressor assembly is positioned in the string between the electric motor and the ESP. 
     
     
         7 . The method of  claim 1 , further comprising the step of pumping the compressed production fluid to the surface. 
     
     
         8 . The method of  claim 1 , wherein the compressor assembly includes a rotary compressor element attached to a compressor drive shaft, and further comprising the step of driving the rotary compressor drive shaft by a drive shaft of the electric motor. 
     
     
         9 . The method of  claim 1 , further comprising the step of separating at least some free gas from the production fluid using a gas separator tool prior to the step of compressing the production fluid using the compressor assembly. 
     
     
         10 . The method of  claim 1 , wherein the compressor assembly allows fluid flow therethrough without fluid flow restriction. 
     
     
         11 . The method of  claim 1 , wherein the step of compressing further comprises the step of supporting a drive shaft of the compressor assembly with at least one bearing. 
     
     
         12 . The method of  claim 11 , wherein the at least one bearing comprises a corrosion-resistant bushing. 
     
     
         13 . The method of  claim 1 , wherein the step of compressing the production fluid using the compressor assembly, further comprises rotating a helical compressor blade within a compressor tubular. 
     
     
         14 . The method of  claim 13 , wherein a clearance between the helical compressor blade and the compressor tubular is minimized. 
     
     
         15 . The method of  claim 13 , wherein all production fluid in the interior passageway is compressed in the compressor assembly. 
     
     
         16 . An apparatus for lifting production fluid from a subterranean wellbore extending through a hydrocarbon-bearing formation to the surface, the apparatus comprising:
 an Electrical Submersible Pump (ESP) having a fluid intake;   a compressor having at least one compressor stage for compressing production fluid, the compressor stage having a fluid discharge in fluid communication with the ESP fluid intake, a generally helical compressor blade mounted for rotation in a generally cylindrical chamber, and wherein the compressor blade entrains or dissolves a free gas component of a production fluid into a liquid component of the production fluid; and   an electrical motor for powering the ESP and compressor.   
     
     
         17 . The apparatus of  claim 16 , further comprising a plurality of adjacent compressor stages arranged in series, with each compressor stage discharging fluid to an intake of an adjacent compressor stage or to the ESP intake. 
     
     
         18 . The apparatus of  claim 17 , wherein the plurality of compressor stages, in combination, increase pressure of the production fluid to a pressure within the operating range of the ESP intake. 
     
     
         19 . The apparatus of  claim 16 , wherein each compressor stage increases production fluid pressure by between about 8 psi (55 kPa) and 32 psi (221 kPa). 
     
     
         20 . The apparatus of  claim 16 , wherein the one or more compressor stages increase production fluid pressure by between about 8 psi (55 kPa) and 60 psi (414 kPa). 
     
     
         21 . The apparatus of  claim 16 , wherein a compressor stage further comprises at least one compressor shaft operably connected to a drive shaft of the electric motor, and at least one compressor shaft bearing.