Method and system for monitoring fluid flux in a well

Abstract

Fluid flux in a fluid injection and/or hydrocarbon fluid production well is monitored in a cost efficient and accurate manner by inducing the fluid flux to move an acoustic emission device in a longitudinal direction through the well, measuring a longitudinal velocity (v) of the acoustic emission device at various longitudinally spaced locations in the well using a fiber optical Distributed Acoustic Sensing (DAS) assembly which monitors the longitudinal position of the acoustic emission device against time along at least part of the length of the well, and monitoring the fluid flux at various locations along the length of the well on the basis on the measured velocity (v) of the acoustic emission device.

1 . A method for monitoring fluid flux in a fluid production and/or injection well comprises:
 inducing the fluid flux to move an acoustic emission device in a longitudinal direction through the well;   measuring at various longitudinally spaced locations a longitudinal position of the acoustic emission device against time using a fiber optical Distributed Acoustic Sensing (DAS) assembly which is arranged along at least part of the length of the well;   calculating a longitudinal velocity of the acoustic emission device at the longitudinally spaced locations on the basis of the measured longitudinally spaced locations against time; and   monitoring the fluid flux at various locations along the length of the well on the basis of the measured longitudinal velocities of the acoustic emission device at the longitudinally spaced locations.   
     
     
         2 . The method of  claim 1 , wherein the well has a permeable fluid inflow and/or injection region and the fluid inflow and/or injection rates at various locations along the length of this region are derived from changes of the longitudinal velocity of the acoustic emission device at various longitudinally spaced locations along the length of this region. 
     
     
         3 . The method of  claim 2 , wherein the well is a fluid injection well through which fluid is injected through perforations in a permeable downhole section of the well into an underground oil and/or gas containing formation and the acoustic emission device has a substantially spherical outer circumference with a larger width than the widths of the perforations. 
     
     
         4 . The method of  claim 3 , wherein a plurality of acoustic emission devices are stored in a container near a wellhead of the injection well from which one of the stored acoustic emission devices is released from time to time into the injection well. 
     
     
         5 . The method of  claim 2 , wherein the well is a hydrocarbon fluid production well and the DAS assembly spans at least a substantial part of the length of an permeable inflow section of the well that traverses a hydrocarbon fluid containing formation and the acoustic emission device is launched near an upstream end of the permeable inflow section to monitor the influx of hydrocarbon fluid at various longitudinally spaced locations along the length of the permeable inflow section. 
     
     
         6 . The method of  claim 5 , wherein a plurality of acoustic emission devices are stored in a container near a bottom of the production well from which from time to time one of the stored acoustic emission devices is released into the well. 
     
     
         7 . The method of  claim 1 , wherein the density of the acoustic emission device is substantially similar to the density of the fluid in a lower part of the well. 
     
     
         8 . A method of producing hydrocarbon fluid from a hydrocarbon fluid containing formation, wherein the fluid injection and production rates in fluid injection and hydrocarbon fluid production wells traversing the formation are monitored in accordance with the method according to  claim 1 . 
     
     
         9 . A system for monitoring fluid flux in a fluid production and/or injection well, the system comprising:
 an acoustic emission device which is configured to be moved by the fluid flux in a longitudinal direction through the well;   a fiber optical Distributed Acoustic Sensing (DAS) assembly which is arranged along at least part of the length of the well and configured to measure at various longitudinally spaced locations a longitudinal position of the acoustic emission device against time;   means for calculating a longitudinal velocity of the device at the longitudinally spaced positions on the basis of changes of the measured longitudinal positions against time; and   a display for monitoring the fluid flux at various locations along the length of the well on the basis of the calculated velocities of the acoustic emission device at the longitudinally spaced locations.   
     
     
         10 . The system of  claim 9 , wherein the well has a permeable fluid inflow and/or injection region and the display is furthermore configured to monitor fluid influx and/or injection rates at various locations along the length of this region, on the basis of changes of the longitudinal velocity of the acoustic emission device along the length of this region. 
     
     
         11 . The system of  claim 10 , wherein the well is a fluid injection well through which fluid is injected through perforations in a perforated downhole section of the well into an underground oil and/or gas containing formation and the acoustic emission device has a substantially spherical outer circumference with a larger width than the widths of the perforations. 
     
     
         12 . The system of  claim 11 , wherein a plurality of acoustic emission devices are stored in a container which is configured to be stored near a wellhead of the injection well and which has a release mechanism that is configured to release from time to time one of the stored acoustic emission devices into the injection well. 
     
     
         13 . The system of  claim 9 , wherein the well is a hydrocarbon fluid production well through which hydrocarbon fluid is produced from an underground hydrocarbon fluid containing formation that is traversed by a permeable inflow section of the well and the DAS assembly spans at least a substantial part of the permeable inflow section and the acoustic emission device is launched near an upstream end of the permeable inflow region to monitor the influx of hydrocarbon fluid at various longitudinally spaced locations along the length of the inflow region. 
     
     
         14 . The system of  claim 13 , wherein a plurality of acoustic emission devices are stored in a container which is configured to be installed at or near a bottom of the production well and which has a release mechanism that is configured to release from time to time one of the stored acoustic emission devices into the production tubing. 
     
     
         15 . The system of  claim 9 , wherein the acoustic emission device has a density which is substantially similar to the density of the fluid in a lower part of the well.