Patent Publication Number: US-8528395-B2

Title: Monitoring fluid pressure in a well and retrievable pressure sensor assembly for use in the method

Description:
The present application claims priority from European Patent Application 04253033.6 filed 5 Jul. 2004. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a method for monitoring fluid pressure in a well and to a retrievable pressure assembly for use in the method. 
     2. Background of the Art 
     U.S. Pat. No. 6,464,004 discloses installing a pressure monitoring assembly in a side pocket of a production tubing in a well, such that the assembly can be easily installed and retrieved into and from the side pocket by means of a kickover tool that is suspended from a wireline. 
     The known assembly is configured to monitor the pressure in an annulus between the production tubing and well casing by a pressure gauge, which is arranged in an annular space between the housing of the pressure sensing assembly between a pair of annular seals that are mounted on the housing, which space is in fluid communication with the annulus via an opening in the wall of the side pocket. 
     The known assembly may also be configured to monitor the pressure in a tubing below an electrical submersible pump, generally known as an ESP, in a well by arranging a pressure monitoring assembly in a side pocket of a production tubing above the ESP and by providing a bypass conduit which is at its lower end connected to the interior of the tubing below the ESP and at its upper end connected to the opening in the wall of the side pocket that is located between the annular seals of the pressure sensing assembly. 
     A disadvantage of the known pressure sensing assembly is that the presence of a bypass conduit makes the assembly complex and fragile. A further disadvantage is that the known pressure sensing assembly is not configured to monitor the pressure difference across the ESP or other pump. 
     U.S. Pat. No. 6,568,478 discloses a gas-lift valve with a venturi which stabilises the flux of lift gas injected from the annulus into the crude oil production tubing. The known valve may be retrievably inserted in a side pocket that provides fluid communication between the interior of the production tubing and the surrounding annulus. 
     SUMMARY OF THE INVENTION 
     The method according to the invention for monitoring the pressure in a well comprises: 
     connecting a pump to a production tubing within the well such that the pump pumps well effluents from an inflow region of the well into the production tubing; 
     providing the production tubing with a side pocket which comprises an opening that provides fluid communication between the interior of the side pocket and an annular space surrounding the production tubing, which space is in fluid communication with the inflow region of the well; 
     inserting a pressure sensor assembly into the side pocket such that the opening is located between a pair of annular seals that are mounted on the housing of the pressure sensor assembly; and 
     monitoring the pressure difference across the pump by inducing the pressure sensor assembly to measure a pressure difference between a section of the side pocket which is connected in fluid communication with the interior of the production tubing and a section of the interior of the side pocket which is located between the annular seals; wherein the pressure sensor assembly comprises: 
     a first pressure sensor which measures the fluid pressure in the interior of the side pocket which is connected in fluid communication with the interior of the production tubing; 
     a second pressure sensor which measures the fluid pressure in the section of the interior of the side pocket which is located between the annular seals; and 
     means for monitoring the difference of the fluid pressures measured by the first and second pressure sensor and for transmitting the measured pressures and/or pressure difference to a data transmission and/or data storage unit. 
     The housing of the pressure sensor assembly may have a substantially tubular shape and may be provided with a fishing neck for connecting the pressure sensor assembly to a wireline operated or robotic installation tool, which is configured to lower and raise the pressure sensor assembly through the production tubing, and to insert and remove the pressure sensor assembly into and from the side pocket. 
     The pressure data may be transmitted to surface by a wireless transmission system or stored in the retrievable assembly for subsequent analysis after retrieval of the assembly from the well. 
     Optionally the pressure sensor assembly is equipped with a data storage unit in which the monitored pressures and/or pressure difference data are stored and the stored data are transferred to a data processing unit after retrieval of the pressure sensor assembly from the well. 
     Alternatively, the pressure sensor assembly is provided with a data transmission unit for wireless transmission of the measured pressure difference to a receiver which is connected to a monitoring and/or control assembly for monitoring and/or controlling the performance of the pump and with a battery for supplying electrical power to the data transmission unit and to the pressure sensor assembly. 
     The pump may be an electrical submersible pump (ESP), which is connected to the production tubing within an oil production well. 
     These and other features, embodiments and advantages of the method and assembly according to the present invention will become apparent from the accompanying claims and abstract and from the following detailed description of a preferred embodiment in which reference is made to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic longitudinal sectional view of a pressure monitoring assembly according to the invention, which is retrievably installed in a side pocket in a production tubing above an ESP in an oil production well. 
     
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
       FIG. 1  shows a well  1  for production of crude oil, water and/or other fluids, which traverses an underground formation  2 . The well  1  comprises a well casing  3 , which is provided with perforations  4  through which fluid flows into the well  1  as illustrated by arrows  5 . 
     A production tubing  6  is suspended within the well  1  from a wellhead (not shown) such that an electrical submersible pump (ESP)  7  is located above the inflow zone  8  for pumping fluid into the production tubing  6 . 
     The production tubing  6  is provided with a side pocket  9  in which a pressure monitoring assembly  10  is arranged. 
     The side pocket  9  comprises an opening  13  which is located between a pair of annular seals  14  and  15  such a annular section  16  between the inner wall of the side pocket  9  and the outer wall of the tubular housing of the pressure monitoring assembly  10  is created in which the fluid pressure is substantially similar to the fluid pressure in the annular space  12  between the production tubing  6  and well casing  3 . The fluid pressure in the annular space  12  is slightly lower than the fluid pressure pi at the pump inlet openings  17 , and/or the Bottom-Hole Pressure (BHP), because of the hydrostatic fluid pressure of the fluid column between the inlet openings  17  of the ESP and the opening  13 . 
     The pressure sensor assembly  10  comprises a first pressure sensor  20  which measures the fluid pressure p 1  in the annular section  16  and a second pressure sensor  21  and a second pressure sensor  21 , which measures the fluid pressure p 2  in the interior  22  of the production tubing  6 . 
     The pressure sensor assembly  10  is provided with a processor for monitoring the pressures p 1  and p 2  and the difference Δp between the pressures p 1  and p 2 . The thus monitored pressures and pressure difference may be stored in a memory and/or are transmitted by a wireless signal transmitter  23  to a receiver (not shown) at or near the wellhead and/or the ESP  7 . 
     The pressure sensor assembly  10  according to the invention provides a very efficient and simple device for monitoring the pressure difference Δp between the interior  22  and exterior  12  of the production tubing  6 , which pressure difference is substantially similar to the pressure difference Δp=p d −p i  between the outlet and inlet openings of the ESP  7 . 
     Instead of transmitting the monitored pressure difference and/or other pressure data to surface by means of a wireless signal transmitter  23  the monitored pressure data may be stored in the memory of the pressure sensor assembly  10  over a prolonged period of time such after retrieval of the pressure sensor assembly  10  to surface by a robotic or wireline operated kickover tool the stored pressure data are transferred to a pressure data processing unit at the earth surface. 
     The pressure data processing unit may provide a graphical display of the monitored pressure difference Δp, and/or the pump inlet pressure p i  and/or Bottom-Hole Pressure (BHP) over time, such that any deviation of the monitored pump inlet pressure p i , Bottom Hole Pressure (BHP) and/or pressure difference Δp from a pressure p i , Bottom-Hole Pressure (BHP) and/or pressure difference Δp at which the ESP  7  operates optimally can be assessed and analysed, and an operator may subsequently adjust the settings of the ESP  7 . 
     The housing of the pressure sensor assembly may have a substantially tubular shape and may be provided with a fishing neck for connecting the pressure sensor assembly to a wireline operated or robotic installation tool, which is configured to lower and raise the pressure sensor assembly through the production tubing, and to insert and remove the pressure sensor assembly into and from the side pocket. 
     The pressure data may be transmitted to surface by a wireless transmission system or stored in the retrievable assembly for subsequent analysis after retrieval of the assembly from the well. 
     Optionally the pressure sensor assembly is equipped with a data storage unit in which the monitored pressures or pressure difference data are stored and the stored data are transferred to a data processing unit after retrieval of the pressure sensor assembly from the well. 
     Alternatively, the pressure sensor assembly is provided with a data transmission unit for wireless transmission of the measured pressure difference to a receiver which is connected to a monitoring or control assembly for monitoring and/or controlling the performance of the pump and with a battery for supplying electrical power to the data transmission unit and to the pressure sensor assembly. 
     The pump may be an electrical submersible pump (ESP), which is connected to the production tubing within an oil production well. 
     These and other features, embodiments and advantages of the method and assembly according to the present invention will become apparent from the accompanying claims and abstract and from the following detailed description of a preferred embodiment in which reference is made to the accompanying drawings.