Estimating flow rate at a pump

Abstract

A method for determining an estimated flow rate of fluid flow in a pump comprises: obtaining measurements of the pressure and temperature of fluid at the intake to the pump, the pressure and temperature of the fluid at the discharge from the pump, and the electrical power supplied to the pump; determining values representing either the density of the fluid and the specific heat capacity of the fluid, or the specific fluid enthalpy based on measurements and/or historical data; and calculating an estimated efficiency of the pump and an estimated flow rate of the fluid based on the measured electrical power, the measured temperatures, the measured pressures, the determined value for density and the determined value for specific heat capacity or the determined value for specific fluid enthalpy.

1 . A method for determining an estimated flow rate of fluid flow in a pump system including a pump, the method comprising:
 obtaining measurements of the pressure and temperature of fluid at the intake to the pump, the pressure and temperature of the fluid at the discharge from the pump, and the power supplied to the pump system;   determining values representing either the density of the fluid and the specific heat capacity of the fluid, or the specific fluid enthalpy based on measurements and fluid models and/or historical data; and   calculating an estimated efficiency of the pump and an estimated flow rate of the fluid based on the supplied power, the measured temperatures, the measured pressures, the determined value for density and the determined value for specific heat capacity or the determined value for specific fluid enthalpy, and   comparing the calculated estimated efficiency of the pump to a manufacturer's prescribed efficiency values of the pump, and when the calculated estimated efficiency of the pump is outside of the manufacturer's prescribed efficiency values, issuing an alert which indicates at least one of an error in measured input data, wear on the pump, damage to the pump, or failure of the pump.   
     
     
         2 . A method as claimed in  claim 1 , wherein the fluid passing through the pump is sampled or collected downstream of the pump, with measurements being taken to determine values for density and specific heat capacity and/or for specific enthalpy. 
     
     
         3 . A method as claimed in  claim 1 , wherein estimated values for fluid density, specific heat capacity and/or specific fluid enthalpy are used, with the estimated values being derived from fluid property models and from the pressures and temperatures that are measured at the pump intake and discharge. 
     
     
         4 . A method as claimed in  claim 1 , comprising modifying a pump device in order that it includes temperature and pressure sensors for the intake and the discharge. 
     
     
         5 . A method as claimed in  claim 1 , comprising determining if a stable flow condition exists before using measured temperature and pressure values in the calculation of estimated efficiency and flow rate. 
     
     
         6 . A method as claimed in  claim 1 , comprising allowing a predetermined time period to elapse after the system is initiated or after an unstable flow condition is known to be present or has been detected. 
     
     
         7 . A method as claimed in  claim 6 , comprising allowing a predetermined time period to elapse after a change is made to the control of the pump or to other flow control devices affecting the flow at the pump. 
     
     
         8 . A method as claimed in  claim 1 , comprising checking for changes above a certain threshold in one or more of the measured pressures, the measured temperatures, the power supplied to the pump, or the calculated pump efficiency during a predetermined time period before using measured temperature and pressure values in the calculation of estimated efficiency and flow rate. 
     
     
         9 . A method as claimed in  claim 6 , wherein the predetermined time period is at least 5 minutes. 
     
     
         10 . A method as claimed in  claim 1 , comprising comparing the discharge and intake temperatures and checking that the discharge temperature is higher than or at least the same as the intake temperature. 
     
     
         11 . A method as claimed in  claim 1 , wherein the step of calculating the estimated efficiency for the pump and the estimated flow rate is carried out based on the assumption that the power supplied to the pump is converted to mechanical energy and to heat in the pumped fluid, and that there is no loss of either mass or heat. 
     
     
         12 . A method as claimed in  claim 1 , wherein mass and energy balances are used to determine the flow rate based on the measured pressure and temperature values, the known cross-sectional area for the pump, and the determined values for density and specific heat capacity or for specific fluid enthalpy. 
     
     
         13 . A method as claimed in  claim 1 , comprising using calibration data for the pump to determine a viscosity for the mixed fluid based on the estimated flow rate and on the estimated pump efficiency. 
     
     
         14 . A method as claimed in  claim 1 , comprising using calibration data for the pump to determine the gas fraction in the pump for compressible fluids based on the estimated flow rate and the efficiency. 
     
     
         15 . A method as claimed in  claim 1 , wherein the pump is a centrifugal pump. 
     
     
         16 . A method as claimed in  claim 1 , wherein the pump is an electrical submersible pump (ESP). 
     
     
         17 . A method as claimed in  claim 1 , wherein the method is used to estimate flow rates for multiphase fluids in the oil and gas industry. 
     
     
         18 . A computer programme product comprising instructions that, when executed, will configure a data processing device to carry out a method as claimed in  claim 1 . 
     
     
         19 . A computer programme product comprising instructions that, when executed, will configure a data processing device to receive measurements of pressure and temperature of fluid at an intake to a pump, pressure and temperature of the fluid at a discharge from the pump, and electrical power supplied to the pump; to receive or to determine values representing the density of the fluid and the specific heat capacity of the fluid, or the specific fluid enthalpy, based on measurements and/or historical data; to calculate an estimated efficiency for the pump and an estimated flow rate of the fluid based on the measured electrical power, the measured temperatures the measured pressures, the known cross-sectional area, the value for density and the value for specific heat capacity or the value for specific fluid enthalpy, and to compare the calculated estimated efficiency of the pump to a manufacturer's prescribed efficiency values of the pump, and when the calculated estimated efficiency of the pump is outside of the manufacturer's prescribed efficiency values, to issue an alert which indicates at least one of an error in measured input data, wear on the pump, damage to the pump, or failure of the pump. 
     
     
         20 . An apparatus for estimating flow rate of fluid at a pump, the apparatus comprising a data processing device arranged to receive measurements of pressure and temperature of fluid at an intake to a pump, pressure and temperature of the fluid at a discharge from the pump, and electrical power supplied to the pump; to receive or to determine values representing the density of the fluid and the specific heat capacity of the fluid and/or the specific fluid enthalpy based on measurements and/or historical data; to calculate an estimated efficiency for the pump and an estimated flow rate of the fluid based on the measured electrical power, the measured temperatures the measured pressures, the known cross-sectional area, the value for density and the value for specific heat capacity or the value for specific fluid enthalpy, and to compare the calculated estimated efficiency of the pump to a manufacturer's prescribed efficiency values of the pump, and when the calculated estimated efficiency of the pump is outside of the manufacturer's prescribed efficiency values, to issue an alert which indicates at least one of an error in measured input data, wear on the pump, damage to the pump, or failure of the pump.