Patent Publication Number: US-2012034103-A1

Title: Method and apparatus for monitoring of esp

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is based on and hereby claims priority to International Application No. PCT/RU2009/000069 filed on Feb. 13, 2009, the contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND 
     The invention is directed to a method and apparatus for monitoring an ESP. 
     Oil has to be pumped from underground reservoirs in onshore industry and under water in offshore industry. At most a multiphase flow of oil and gas and eventually water is existent. Therefore electrical submersible pumps (ESP) are needed. 
     A safe monitoring of the ESP is important. Such monitoring systems must detect gas content in the well liquid flow in order to shut down the pump if too high gas content in the well liquid occurs to prevent damage of the pump. 
     Downhole monitoring systems are available. There are the following publications which provide technical background: 
     “Boletin Quincenial”, Aug. 31, 1997, describes a multiphase flowmeter suitable for well testing especially with a pump system. WO 2006/115931 A2 describes a multiphase flowmeter and a data system with different units outside the borehole. EP 0 684 458 A2 describes a multiphase flowmeter for measuring the flow rate of multiphase fluids such as oilwell effluents, containing liquid hydrocarbons, gas and water, which is based on differential pressure measurements. EP 1 022 429 A1 describes a multi purpose riser which is inside the oil-pipeline. The US 2005/0268702 A1 describes a non intrusive multiphase flowmeter whereby two physical parameters of the flow are measured for determining the density of the mixture. The U.S. Pat. No. 4,604,902 A describes techniques useful in mass-flowmeters for multiphase flows. 
     Further WO 02/044664 A1 describes a multiphase flowmeter using multiple pressure differentials for signal generation. Especially the WO 2007/114707 A2 describes an acoustic multiphase meter, which includes an ultrasound emitter and an ultrasound receiver for the response signals. 
     All monitoring or measuring systems described in the preceding documents are working on one of the three phenomena and/or principles for multiphase flow measurements. These are: 
     1) measuring of pressure drop and correlation of pressure drop with the flow void fraction. 
     2) using radioactive source or ultrasonic source to measure the velocity and the flow void fraction and 
     3) semi online measurement separating the different phases of the multiphase flow. 
     The apparatuses known by the preceding state or art are quite complicated. 
     SUMMARY 
     Therefore it is one possible object to find other phenomena for monitoring ESP. It is a further possible object to create an apparatus for the method which is cost efficient and could be integrated in existing systems. 
     The inventors propose a monitoring system, which allows controlling the pumps—if needed—to shut the pumps down, for example if too high gas content in the well liquid occurs. This is realized by at least one acoustic detector which is placed on a pump intake (see  FIG. 1  of the Detailed Description). 
     Depending on the gas void fraction in the well liquid the detector delivers different signals which are significant for the pumped fluid media and the different phases of the fluid media. In this way one can identify the gas fraction in the well liquid and thus control the pump. 
     This monitoring system can be made also in combination with other measuring systems for instance double wall tube for phase separation, pressure drop, pH-evaluation and/or composition measuring system. 
     One innovative step is the use of acoustic sensors for pump monitoring and measurement of the gas content in the well liquid. There is no active sound emitter like disclosed in WO 2007/114707 A2, but the use of the impact sound with an acoustic sensor. This is advantageous in view of the technical complexity and also in view of joined costs. 
     Such monitoring systems may have different shape, assembling and might be placed on different positions. 
     In any case the gas fraction in the media flow is identified. This is designated from the gas void fraction in the well liquid. 
     The pump may be controlled by identifying the gas fraction in the well liquid. By delivering different control signals from the detector the pump will be stopped when the gas fraction in the well liquid is exceeding a given threshold. 
     Using the method with the new monitoring system can prevent damage of pumps caused by a too high gas content in the well liquid. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects and advantages of the present invention will become more apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  a projection of a facility for well liquid pumping with a bore hole (well) and the pump components and 
         FIG. 2  a system with hard- and software components for evaluating the measurements. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
     In  FIG. 1  a bore hole is shown in cross section and characterized with numeral  1 . The bore hole  1  has the depth of some thousand meters, for example  3 , 000 m from the ground of earth, and a diameter of for example 4″ (inches). The bore hole  1  leads from a below ground oil reservoir (not shown) and is quite narrow in view of length. The bore hole  1  can be also situated under water from the sea bottom to the reservoir. The fluid conveyed from the reservoir to ground is normally a mixture of oil, gas and water. In  FIG. 1  numeral  5  characterized such a multiphase mixture flow. 
     In the bore hole  1  there is installed a so called ESP  11  (electrical submersible pump).The ESP  11  can have some pump sections  10  for pumping the well liquid from the well to surface. Also ESP has a pump intake  13  and can include a gas separator. 
     The ESP  11  has a motor section(s) with an electrical motor  14 . The motor  14  of the ESP  11  has a motor protector  15 . Such a motor protector is known in the art. 
     There could be also an own monitoring system  18  for the ESP  11 . This is also known in the art. 
     Further there is at least an acoustic sensor  21  which is joined to the motor  14  and/or placed on the pump section  10 . The acoustic sensor  21  is part of an acoustic monitoring system  20  with hard- and software-components shown in  FIG. 2 . These hard- and software-components can control the pump system  10  and especially stop the pump motor  14  preventing damages. 
     There could be more than one acoustic sensor, which are all part of a sensor system  20  with a monitoring unit for evaluating which are shown in  FIG. 2 . 
     The evaluating system has to be suitable for discriminating signals based on oil pumping from signals based on gas pumping or based on gas voids. Also signals based on pumping of water should be discriminated from signals based on pumping of oil. 
     In  FIG. 2  the components  22  to  31  form the acoustic monitoring system of  FIG. 1 : There is a first input  22  of a line for data transfer from the pump control system to the pump monitoring system  18 . Additionally there is a second input  23  of a line for data transfer from the pump monitoring system  18  to the pump control system. 
     There is an input  24  for an acoustic signal based on the acoustic sensor  21  and acoustic sensor system  20  of  FIG. 1 . The acoustic signals are dependant on fluid properties, for example the properties of two-phase flow and/or three phase flow, which is shown in unit  25 , which is followed by a correction unit  26  for signal offset correction. 
     In the correction unit  26  the acoustic signal offset which is shown in unit  27  is subtracted. This means that the noise from the motor, from bearings and other mechanical parts will be eliminated. The resulting signal without offset is shown in unit  28 . 
     In accordance to the measurements and the evaluation shown in unit  28  the ESP  11  of  FIG. 1  could be controlled automatically whereby a decision unit  29  is followed. 
     Further to the self-acting control specific requirements of the customer can be incorporated in the described system via data inputs  30 ,  31  for the decision unit  29 . 
     Other signals for monitoring the state variables, for example pressure drop, pH-evaluation and/or composition measuring system could be combined with the acoustic monitoring system. 
     In any case there are defined correlations between the fluid properties, especially of oil, gas and water mixture flow, and the acoustic signal. A stop of the ESP  11  can be triggered if necessary. It will be actuated in situations especially when the gas fraction in the well liquid is exceeding a given threshold, because of the danger of undesirable damages in the whole oil conveying facility. 
     In accordance with the figures a method had been described for monitoring ESP for producing oil, gas, water or other fluid media, which pump is driven by an electrical motor, acoustical phenomena of the motor and/or the pump are used as state variable for pumping the media. The acoustic phenomena are measured as electrical signals and the electrical signals are discriminated in respect to the pumped media. In the apparatus for monitoring of ESP, with a pump for pumping a mixture of oil, gas and water, the pump is driven by a motor. At least one acoustic sensor is placed in the near of the pump system and/or pump motor. 
     The invention has been described in detail with particular reference to preferred embodiments thereof and examples, but it will be understood that variations and modifications can be, effected within the spirit and scope of the invention covered by the claims which may include the phrase “at least one of A, B and C” as an alternative expression that means one or more of A, B and C may be used, contrary to the holding in  Superguide  v.  DIRECTV,  69 USPQ2d 1865 (Fed. Cir. 2004).