Patent Publication Number: US-7588080-B2

Title: Method for installing well completion equipment while monitoring electrical integrity

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application claims priority to provisional application Ser. No. 60/664,485, filed Mar. 23, 2005. 

   FIELD OF THE INVENTION 
   This invention relates in general to running into a well downhole completion equipment having electrical components, and in particular to a method for installing a submersible pump assembly while monitoring the integrity of the electrical components of the assembly. 
   BACKGROUND OF THE INVENTION 
   Electrical submersible pumps (ESP) are commonly used in oil wells for pumping oil and formation water to the surface. An ESP comprises a pump having a downhole electrical motor. The pump typically is a centrifugal pump having a large number of stages, each stage having an impeller and a diffuser. Alternately, the pump could be another type, such as a progressing cavity pump. The ESP may also have one or more sensors for sensing well parameters such as pressure and temperature. 
   Normally the ESP is lowered into the well on production tubing which comprises joints approximately 30 feet in length secured together by threads. Alternately, the tubing could comprise continuous coiled tubing. A power cable is connected to the motor of the pump while it is at the surface and deployed from a reel while lowering into the well. 
   The ESP and power cable are subject to being damaged during running. Damage can result due to striking objects in the well, vibration, shock or from the well temperature. If the problem is discovered only after the ESP is completely installed, expense and time are incurred to pull the ESP, tubing and power cable from the well. The well could be thousands of feet deep. Consequently, it is not uncommon for the operator to stop the rig and connect the ends of the power cable to equipment on the surface to check the integrity of the system. Stopping the rig to perform these test adds to the running time for the ESP. 
   Downhole completion equipment other than ESPs also encounter the same problem. For example, sliding sleeve subs, packers, gravel packing tools, sand control screens and the like may include electrical actuators and/or sensors such as position indicating devices. These types of completion equipment are also run on tubing and may have an electrical line deployed from a reel. 
   SUMMARY OF THE INVENTION 
   In the method of this invention, the completion equipment is lowered into the well in a non operational state while deploying the electrical line. Without causing the completion equipment to enter an operational state, test power is supplied to the electrical line periodically and a response is displayed at the surface to monitor the integrity of the completion equipment and the electrical line. When at a desired depth, the completion equipment is secured in the well and placed in an operational state. 
   The electrical line is preferably wound on a reel and deployed from the reel while the completion equipment is lowered into the well. A battery-powered test unit is mounted to the reel and releasably connected to the electrical line. The test power to the electrical line is supplied by the unit, which also receives the response. Preferably, the response is transmitted from the unit to a remote monitor by radio frequency. 
   In one example, the completion equipment comprises an electrical submersible pump assembly, and the test power is supplied over the power cable leading to the motor of the pump assembly. Preferably, the pump assembly includes a pressure sensor, and the test power is sent to the pressure sensor. 
   In another example, the test power is used to measuring a resistance to ground of the electrical line. In a further example, the completion equipment comprises a submersible pump assembly, and the test power is used to measure an impedance of the motor of the pump assembly. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic view illustrating an ESP being lowered into a well while monitoring the integrity of the electrical cable and ESP in accordance with this invention. 
       FIG. 2  is a schematic view illustrating a portion of the cable reel shown in  FIG. 1  and a test unit mounted thereto. 
       FIG. 3  is a simplified electrical schematic illustrating monitoring resistance and impedance of the power cable conductors in accordance with this invention. 
       FIG. 4  is a simplified electrical schematic illustrating monitoring the impedance of the electrical motor in accordance with this invention. 
       FIG. 5  is an electrical schematic of an alternate method for monitoring the integrity of an ESP and power cable. 
       FIG. 6  is an enlarged schematic illustrating a portion of the cable reel in  FIG. 5  and a test unit mounted thereto. 
       FIG. 7  is a schematic view of a packer being installed in a well in accordance with this method. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 1 , a well  11  has one or more strings of casing  13  installed within the well. A production tree  15  is located at the upper end of well  11  for controlling the flow of the well fluids from well  11 . 
   An electrical submersible pump assembly  17  (“ESP”) is shown being lowered into well  11 . ESP  17  includes a centrifugal pump  19  having a large number of stages of impellers and diffusers. A seal section  21  connects the lower end of pump  19  to a motor  23 . In some instances, a sensor unit  25  is secured to the lower end of motor  23  for providing signals corresponding to pressure and temperature. ESP  17  could alternately employ a progressing cavity type pump, which utilizes a stationary stator having a helical cavity. A rotor with helical lobes rotates within the stator, the rotor being driven by an electrical motor. 
   In this example, a string of production tubing  27  is employed to lower ESP  17  into the well. Production tubing  17  is normally made up of individual sections of pipe, each about thirty feet in length, the joints of pipe being secured together by threaded ends. A lifting device, comprising a set of elevators  29  engages the upper end of tubing  27 , the elevators  29  being supported by a derrick with draw works (not shown). Alternately, tubing  27  could be continuous or coiled tubing deployed from a coiled tubing unit, rather than rig elevators  29 . 
   A power cable  31  connects to motor  23  via a motor lead, which is not shown separately and is considered herein to be a part of power cable  31 . Power cable  31 , in this example, extends alongside tubing  27  and is secured at intervals by clamps  33 . Power cable  31  extends over a sheave  35  suspended from the derrick (not shown) to a reel  37 . Power cable  31  is wrapped around and stored on reel  37 , which is brought to the site of well  11  when ESP  17  is to be deployed. Reel  37  has a stand  39  for supporting reel  37  on the ground or on a vehicle. Reel  37  also has a hub  41  that rotates with reel  37 . 
   A test unit  43  is connected to the upper end of power cable  31  for measuring the integrity of power cable  31  as ESP  17  is lowered into the well. In this embodiment, test unit  43  rotates with reel  37  and sends a wireless signal to a monitor  45  located nearby. Monitor  25  displays a reading to operating personnel of the integrity of cable  31  and motor  23 . Test unit  43  may operate continuously or it may perform the test at selected intervals. 
   Referring to  FIG. 2 , in one embodiment, hub  41  is hollow and has an opening  47  therein for receiving the upper end of cable  31 . Power cable  31  has three insulated electrical conductors  49 A,  49 B and  49 C. Each conductor  49 A, B and C is releasably connected by a conventional connection to test unit  43 . Test unit  43  is releasably mounted to the inner surface of hub  41  for rotation therewith. In this embodiment, a pair of resilient clips  51  engage test unit  43  to retain it with hub  41 . Alternately, test unit  43  could be mounted to the flanges or spokes of reel  37 . Other means of attachment are also feasible, such as a magnetic base on the housing of test unit  43 . 
   Referring to  FIG. 3 , motor  23  is normally a three-phase motor having windings  53 A,  53 B and  53 C. Windings  53 A, B and C may be connected in a Y connection as shown in  FIG. 3  or in a Delta configuration (not shown). For a Y connection, sensor circuit  25 , if employed, is preferably connected to the node between the three windings  53 A, B and C. The connection of windings  53 A, B and C is at the lower end of motor  23  ( FIG. 1 ). 
   One task of test unit  43  is to measure the electrical resistance of each cable conductor  49 A,  49 B and  49 C to each other and to ground. That resistance should be infinite, and if not, it is likely that damage to the electrical insulation of one or more of the conductors  49 A, B and C has occurred. Various circuitry may be employed to monitor that resistance. In this example, a separate Wheatstone bridge circuit  55 ,  57  and  59  is employed to monitor the resistance of each conductor  49 A,  49 C and  49 B, respectively. Alternately, a single bridge circuit could be employed, with a sequencing device switching between each conductor  49 A,  49 B and  49 C. Each bridge circuit  55 ,  57  and  59  has four legs, each containing a resistor R 1 , R 2  and R 3 . Resistors R 1 , R 2 , and R 3  are of known value. One node for the fourth leg is connected to ground, while the other node for the fourth leg is connected to one of the conductors  49 A,  49 B or  49 C. A galvanometer or other current measuring device  61  is connected to the node between R 1  and R 2  and to ground. A power source  65  is connected to the node between R 2  and R 3  and to one of the conductors  49 A,  49 B or  49 C. If desired, a switch  63 ,  67  and  69  may be utilized to electrically turn on and off voltage from power source  65 . 
   Power source  65  is preferably a battery with an inverter so that it will supply DC voltage as well as AC voltage. The DC voltage causes Wheatstone bridges  55 ,  57  and  59  to provide a current measurement that correlates with a resistance value for each of the conductors  49 A,  49 B,  49 C. Current measuring device  61  is connected to a transmitter  70 , which sends the value of the resistance to monitor  45 . When AC power is supplied, the AC current measured by current measuring device  61  correlates with an impedance value for each of the conductors  49 A,  49 B and  49 C. 
   Referring to  FIG. 4 , preferably the impedance of electrical motor  23  is also monitored while deploying ESP  17 . In  FIG. 4 , this is handled by three Wheatstone bridge circuits  71 ,  73  and  75 . Each bridge circuit  71 ,  73  and  75  is configured as in  FIG. 3 , having resistors R 1 , R 2  and R 3  connected in the same manner. Conductors  49 A and  49 C are connected to the fourth leg nodes of bridge circuit  71 . Conductors  49 A and  49 B are connected to the fourth leg nodes of bridge circuit  73 . Conductors  49 B and  49 C are connected to the nodes of the fourth leg bridge circuit  75 . 
   Current measuring device  61  provides to transmitter  70  readings that correspond to the motor  23  impedance. Each bridge circuit  71 ,  73  and  75  is connected to power source  65  for supplying AC voltage. Switches  79 ,  81  and  83  may be employed to block the power source  65  from any one of the bridge circuits  71 ,  73  and  75 . Furthermore, the separate bridge circuits  71 ,  73  and  75  could be consolidated along with bridge circuits  55 ,  57  and  59  into a single bridge circuit for sequential operation. 
   During the installation operation, the operator will assemble ESP  17  and connect power cable  31  to the motor lead of motor  23 . The operator will connect the upper end of power cable  31  to test unit  43 , as illustrated in  FIG. 2 . The operator lowers ESP  17  on tubing  27  while unwinding power cable  31  from reel  37 . From time to time the operator will strap power cable  31  to tubing  27  with clamps  33 . No operational power is supplied to motor  23  while ESP assembly  17  is being lowered into the well, thus pump  19  remains non operational. 
   At all times, the operator will be able to monitor the resistance and impedance of power cable  31 . Test unit  43  ( FIG. 1 ) provides AC and DC current measurements to ground of each conductor  49 A,  49 B and  49 C, as illustrated in  FIG. 3 . These values provide resistance and impedance readings, and transmitter  70  sends signals to monitor  45  to display the measurements to the operator. At the same time, test unit  43  applies AC voltage between conductors  49 A,  49 B and  49 C, as shown in  FIG. 4 , to determine the impedance through motor  23 . The various measurements could be made sequentially. Rather than continuous operation, the test voltage from test unit  43  could be supplied automatically or manually at selected time intervals. If a reading appears that is outside of a selected range, the operator could pull ESP  17  from the well before reaching its final depth. 
   If desired, and depending upon the type of sensor circuit  25 , signals could also be sent to circuitry (not shown) within test unit  43  from sensor circuit  25  over conductors  49 A,  49 B and  49 C. These signals could be converted into pressure and temperature readings and transmitted by transmitter  70  to monitor  45  ( FIG. 1 ). 
   In the embodiment of  FIGS. 5 and 6 , the test unit does not check electrical resistance and impedance, rather it applies test voltage to the downhole sensor circuit  25 . Sensor circuit  25  is conventional and may measure a variety of parameters during operation of motor  23  including well fluid pressure, motor lubricant temperature and vibration. Sensor circuit  25  may be a variety of types, either analog or digital. After installation, a conventional operational power source  85  supplies three-phase AC power over conductors  49 A,  49 B and  49 C to motor  23 . Sensor circuit  25  preferably receives its power from power source  85  over conductors  49 , and the response of sensor circuit  25  is superimposed on conductors  49 . During normal operation, sensor circuit  25  communicates with an operational detector circuit  87  that receives signals typically via power conductors  49 . Operational detector circuit  87  and the method of telemetry with sensor circuit  25  may be conventional. 
   As shown in  FIG. 6 , test unit  89  is mounted by releasable retainer  91  to reel hub  41 . Test unit  89  has a voltage lead  93  that has an alligator clip on its end for securing to one of the conductors  49 . Test unit  89  has a ground lead  95  with an alligator clip that the operator clips preferably to the armor on power cable  31 . 
   Referring again to  FIG. 5 , test unit  89  has a battery  97  and a switch  99  for applying voltage through a test detector circuit  101  to one of the conductors  49 . Test detector circuit  101  may be constructed generally in the same manner as operational detector circuit  87 . When energized, test detector circuit  101  will receive a signal indicating one or more of the parameters being monitored by sensor circuit  25 . Preferably, test detector circuit  101  has a wireless transmitter  103  that transmits the response to a receiver and display or monitor  105  located nearby. 
   In the operation of the embodiment of  FIGS. 5 and 6 , as the pump assembly is lowered into the well, power from operational power supply  85  will remain off. Test detector circuit  101  applies voltage to one of the conductors  49  either continuously or periodically and receives a response from sensor circuit  25 . If a signal is not received from sensor circuit  25 , a component of the system, such as one in pump motor  23 , sensor circuit  25  or power cable  31 , is not functioning properly. The operator would then retrieve the pump assembly to diagnose the fault. While lowering the ESP assembly into the well, it is not necessary that test unit  89  provide accurate readings of the well environment parameters, rather it need only receive an indication that sensor circuit  25  is operational. 
   If the response indicates that the downhole system is functioning properly, the operator will set the pump assembly at the desired point, detach test unit  89  from reel hub  41 , and connect power cable  31  to power source  85 . Power source  85  supplies electrical power to place motor  23  in an operational state, causing the pump of ESP assembly  17  ( FIG. 1 ) to operate. Sensor  25  will be powered by power source  85  and send signals to operational detector circuit  87 . 
     FIG. 7  schematically illustrates that the invention is applicable to downhole completion tools other than ESPs. Well completion assembly  107  could be a variety of devices, such as a gravel packing tool, a packer or bridge plug assembly or a sliding sleeve tool. In the example, a packer running tool  109  is attached to a packer  111  for setting packer  111  in the well. Running tool  109  is shown being lowered on a running string of conduit  113 . An electrical line  115  leads from running tool  109  alongside running string  113 . Electrical line  115  leads to an electrical component within running tool  109 , such as a position sensor. Line  115  is deployed from a reel  117  while running string  113  is being lowered into the well. A test unit  119  similar to test unit  43  ( FIG. 2 ) and test unit  89  ( FIG. 6 ) is releasably mounted to the hub of reel  117  in the same manner as in the other embodiments. Periodically or continuously, test unit  119  provides voltage via line  115  to the sensor in running tool  109  and transmits a wireless signal to a monitor  121 . Monitor  121  will display whether line  115  has maintained conductivity and the sensor is operational. 
   When at the desired setting depth, the operator might disconnect test monitor  119  and complete the setting operation conventionally. Alternately, test monitor  119  could continue to be used to provide voltage to electrical line  115  and signals to monitor  121  to indicate the positions of running tool  109  during the setting operation. After setting packer  111  to place it in an operational state, running tool  109  may be detached from packer  111  and retrieved along with electrical line  115 . 
   Downhole completion assembly  107  could be of a type that when operational, remains connected to the running string  113 , which in that instance, would likely comprise production tubing. For example, rather than packer  111  and running tool  109 , the downhole completion tool could comprise a sliding sleeve for opening and closing access to the interior of the tubing string. Electrical line  115  could either be connected to a sensor that determines whether the sleeve is open or closed, or it could be connected to an electrical actuator, such as a motor or solenoid. If so, after installation, electrical line  115  would remain in the well alongside the tubing and connected to an operational power source at the surface. The test unit would apply voltage to the sliding sleeve component during the running process, then removed along with the reel. 
   The invention has significant advantages. The test unit allows an operator to check the electrical integrity of a downhole completion assembly while it is being run and without slowing down the running process. The method reduces the chances of having to retrieve a downhole completion assembly immediately after it has been installed. The test unit is readily attached to and removed from the electrical line being deployed. Because of the wireless transmitter, the test unit works with conventional reels and needs no slip rings to communicate signals. 
   While the invention has been shown in only three of its forms, it should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes without departing from the scope of the invention.