Operation of a wellhead compressor

Abstract

A method of operating a wellhead compressor includes selecting a plurality of operating points of the wellhead compressor, measuring the tubing pressure at the plurality of operating points of the wellhead compressor and determining an efficiency achieved by the wellhead compressor when operating at each of the operating points based on at least the measured tubing pressure at each of the operating points. A production curve is generated of well pressure as a function of flow rate from a combination of measured data and predicted data. An operating point of the wellhead compressor is selected from the production curve based on at least the efficiency of the wellhead compressor at the selected operating point and the wellhead compressor is operated at the selected operating point. The steps of the method are repeated after operating the wellhead compressor at the selected operating point for a predetermined period of time.

1 . A method of operating a wellhead compressor, the compressor being configured to pump fluid from a well at a tubing pressure, the method comprising:
 selecting a plurality of operating points of the wellhead compressor, wherein the flow rate of fluid pumped by the wellhead compressor varies between the plurality of operating points;   measuring the tubing pressure at the plurality of operating points of the wellhead compressor;   determining an efficiency achieved by the wellhead compressor when operating at each of the operating points based on at least the measured tubing pressure at each of the operating points;   generating a production curve of well pressure as a function of flow rate from a combination of measured data and predicted data,   selecting an operating point of the wellhead compressor from the production curve based on at least the efficiency of the wellhead compressor at the selected operating point; and   operating the wellhead compressor at the selected operating point;   the method further comprising repeating the steps of the method after operating the wellhead compressor at the selected operating point for a predetermined period of time.   
     
     
         2 . The method of  claim 1 ,
 wherein the step of measuring the tubing pressure at a plurality of operating points of the wellhead compressor comprises
 operating the wellhead compressor at a first operating point at which the compressor provides a first flow rate of fluid; 
 measuring a first tubing pressure at the first operating point; 
 operating the wellhead compressor at a second operating point at which the compressor provides a second flow rate of fluid; and 
 measuring a second tubing pressure at the second operating point. 
   
     
     
         3 . The method of  claim 1 ,
 wherein the plurality of operating points include a current operating point, a first operating point at which the wellhead compressor provides a flow rate greater than the current operating point, and a second operating point at which the compressor provides a flow rate less that the current operating point.   
     
     
         4 . The method of optimising gas extraction from a reservoir using a plurality of wellhead compressors, the method comprising:
 operating each of the plurality of wellhead compressors according to the method of  claim 1 ,   wherein the selected operating points of each of the wellhead compressors are selected such that the total flow rate of fluid provided by the plurality of wellhead compressors is equal to or greater than a threshold value.   
     
     
         5 . The method of  claim 4 ,
 wherein the operating points of each of the plurality of compressors are selected such that the combined energy efficiency of the plurality of wellhead compressors is maximised.   
     
     
         6 . The method of  claim 4 ,
 wherein the wellhead compressors are configured to provide pumped fluid to a main compressor, wherein the operating points of each of the plurality of compressors are selected such that an inlet pressure and/or mass flow rate to the main compressor is within a desirable range.   
     
     
         7 . The method of  claim 1 ,
 wherein the wellhead compressor is a screw compressor.   
     
     
         8 . The method according to  claim 1 ,
 wherein the energy efficiency comprises a volumetric energy efficiency.   
     
     
         9 . A device for operating a wellhead compressor, the compressor being configured to pump fluids from a well at a tubing pressure, the device comprising:
 a processor; and   a memory configured to store instructions which when executed by the processor cause the processor to:
 select a plurality of operating points of the wellhead compressor, wherein the flow rate of fluid pumped by the wellhead compressor varies between the plurality of operating points; 
 measure the tubing pressure at a plurality of operating points of the wellhead compressor, wherein the flow rate of fluid pumped by the wellhead compressor varies between the plurality of operating points; 
 determine an efficiency achieved by the wellhead compressor when operating at each of the operating points based on at least the tubing pressure at each of the operating points; 
 generate a production curve of well pressure as a function of flow rate from a combination of measured data and predicted data, 
 select an operating point based on at least the efficiency of the wellhead compressor at the selected operating point; and 
 operate the wellhead compressor at the selected operating point. 
   
     
     
         10 . The method according to  claim 8 , wherein the volumetric energy efficiency is energy usage per m 3  of pumped fluid.