ESP Selection, Deployment and Operation

ESP Selection, Deployment and Operation

1. ESP SELECTION :

Effective Electrical Submersible Pump (ESP) selection is the key to optimizing well production and increasing ESP run life.  Three main categories of factors that affect the selection process of ESP are : 

1. Well Conditions 
2. Field Conditions 
3. Field Challenges

1.1 WELL CONDITIONS :

Well Construction :
Main well parameters that must be taken into consideration while selecting ESP are : 

• Age of the well
• Casing size
• Tubing size
• Well integrity: - cement quality  - casing quality 
• Deviation
• Drilled depth
• Perforation intervals & depth and density

Work Over Events :
Proper Work Over (WO) preparation of the well is based on the following : 

• Current bottomhole conditions
• Detailed information about all previous / historical WO repairs - scraper, reamer, drift diameter and running depth
• Injection capacity test
• Pressure test

Production Characteristics :

Before sizing and selecting an ESP, it is recommended to review well production history and artificial lift methods used. If an ESP was used concentrate on : 

• Previous ESP type, parameters, setting depth
• Well production rate (liquid and oil)
• Well flowing bottomhole pressure (FBHP)
• Current watercut of the well 
• Gas / oil ratio 
• ESP failures root causes 

1. 2 FIELD CONDITIONS :

Each parameter that gives information about the field properties is very important as it represents reservoir and overall field characteristics and gives clearer picture of it. There are numerous parameters that are available nowadays  from  the  client  and  can  be  used  for ESP  sizing  and  designing.  Some  of  the  most  important parameters affecting pump performance will be enumerated in this manual. 

These can be divided into two groups :  

• Primary parameters  
• Secondary parameters

Both those groups are described below : 

Primary Parameters :

• Initial formation pressure
• Current formation pressure (build-up test results, bottomhole gauges)
• Current reservoir temperature
• Permeability (indirectly)
• Porosity (indirectly)
• Oil density
• Oil viscosity
• Productivity Index 
• Reservoir type 
• Oil bubble point pressure

Secondary Parameters : 

• Oil formation volume factor
• Gas oil ratio
• CO2, N2, H2, CO and H2S content
• Salinity
• Specific gravity
• Solids 
• Wax content

1.3 FIELD CHALLENGES : 
The most common field challenges are described below:

Well and Mechanical challenges : 

• Corrosion  (CO2,  H2S  content  information  should  be  studied  attentive  prior  to  design,  selection  and installation of ESP)
• Solids (solid build-up test information about particle mass per volume of fluid) 
• Power supply
• Tubing/casing quality 
• Tubing casing sizes 

Human Challenges :    

• Data collecting
• Improper design 
• Improper well preparation
• Improper installation
• Improper operation
• Improper commissioning 

2. ESP AND SURFACE EQUIPMENT STORAGE, TRANSPORTATION, 

MANIPULATION AND HANDLING :

2.1 ESP AND SURFACE EQUIPMENT STORAGE :

Equipment transportation and handling is another influencing factor in ESP deployment operation. 

Firstly, after ESP’s are manufactured, repaired and tested, they have to be stored in compliance with technical requirements of the Manufacturer and in accordance with safe operating procedures. 

Some of the technical requirements are as follows :  

• All sections must be sealed with shipping caps 
• Motors and protector must be filled with oil. The type of oil will depend on application and whether  conditions
• Pump sections must be filled with antifreeze
• Shelves or racks for equipment storage must have three points of support and must be equipped with placards/labels showing part number, type and model of the section(sections), equipment must not be bended (See Picture #1,#2 – Incorrect ESP Storage) 
• Motors and protectors’ must be stored in the warm warehouse during winter conditions. If there is no facility to keep the equipment in the warm warehouse all the time then 24 hours before installation, motor and protector must be moved into the warm space to be heated up 
• Cable must be stored on reels, safely secured from mechanical damage in the special storage place

SURFACE EQUIPMENT STORAGE :

• In certain countries such as Russia where extreme weather conditions are encountered, additional care and precaution must be taken while storing electrical equipment. It is strongly advised to store items not-in-use in a closed and protected environment.  
• If  electrical  goods  are  to  be  stored,  these  must  be  uncrated  and  stored  in  a ventilated  building  to reduce the accumulation of condensation in the VSD’s, SWB’s etc.  
• If any foreign particles, such as sand, are observed inside the unit, it is necessary to thoroughly clean the unit before putting into operation.  

2.2 EQUIPMENT TRANSPORTATION AND HANDLING

The nature of artificial lift equipment requires special handling procedures which are not commonly used when handling and transporting many other types of pumping systems.  

The most vulnerable parts of equipment while loading/unloading and transportation are : 

• Motor stator – can be bended, it is not acceptable 
• Radial bearings of pump sections 
• Seals of protector
• VSD’s, SWB’s, etc.- electrical components 

 See pictures #3,4 

To reduce the risk of equipment damage, it is necessary that : 

•  All items must be handled in a manner which minimizes shocks. In no case, should an item be allowed to drop
• Follow the instructions of ESP sections and cable strapping 
• The traffic intensity must be taken into consideration at all time as well as the road cover, and cargo special features, and transportation vehicle condition. 
• It is recommended to deliver the equipment to the wellsite directly before installation.  (For prevention of accidental damages of equipment while waiting installation) 
• To transport ESP’s and cables use specially constructed :

          - Shipping boxes

          - Transporting skids (See Draft #1,Picture#5); 

          - Wooden Boxes (Manufacturing packing) (See Picture#6); 

          - Fit for purpose transportation vehicle. 

Construction and principle of Transportation skid operation :

Transportation skid is a welded frame made of metal bended profile. ESP sections must be placed on transverse lath with rubber spacer inside of the frame and must be secured by clamping lath from the above. There are 4 strapping loops situated along the skid. There are some catchers in the upper part of the deck to make it stored within several layers available.

NOTE:
Fig.1 showing how to lift motor section

2.3 SURFACE EQUIPMENT STRAPPING REQUIREMENTS 

Strapping rules :

• Use only four-strops hook for surface equipment strapping (See Fig.2) 
• Hook must enter the loop opening smoothly (See Fig.3) 
• Load must be stropped with the help of all loops that are foreseed for lifting by the project 
• Strops must be loaded with the same tension and the angle between them must be less than 90 deg 
• Strops must be applied without any nodes and kinks

2.4 HANDLING ESP SECTIONS AT THE WELL SITE 

•  ESP unloading operations can be performed using hoisting device, which is located on the transporting vehicle or cathead only. 
• ESP section must be unload to the cleaned from oil and sand workover receiving catwalk; cable reel must be unload directly to the spooler.   
• ESP sections must be unload to the wooden spacers (not less than two units) placed on the receiving sledge – catwalk. 
• ESP sections and cable must be prevented from hitting while handling. 

3. ESP DEPLOYMENT AND START UP PROCEDURE 

3.1 PREPAIRING ESP FOR OPERATION

Individual serial number and type of unit shall be entered in installation report which shall ccompany an ESP at all phases from assembly to pulling and returning ESP for repair to Service center.  

Prior to shipment to a well site have to be checked :

• Electric motor and ESP cable shall be completely tested subject to effective check up program approved by manufacturer
• Protector shall be tested for free shaft rotation and proper seating in spline connection couplings, shaft spline end beat and shaft offset compliance with design drawings, pass hydraulic test, spin testing, including power consumption, vibration of all bearing long three coordinate axes, pumping out (to check tightness of threaded connections), checking the temperature of thrust bearing assembly
• Pump section shall be tested for free shaft rotation and proper seating in spline connection couplings, shaft spline end beat and shaft offset compliance with design  drawings, pass to test bench to etermine such characteristics as the head, pumping  capacity, power consumption, vibration and efficiency 
• DMT has to be tested for pressure, temperature test, vibration test and electrical test. 
• In winter operating sections of a pump shall be coated with frost-proof grease (industrial oil grade or spindle oil type)

3.2 ESP INSTALLATION TOOLS PREPARATION PRIOR TO ASSEMBLING

It is very important to be attentive while installation tools preparation. 

Tools or clamps choice always depends on planned to be assembled ESP type and series.  

As a back up it is always necessary to have the following while assembling :

• Spare couplings
• Plugs for protector fill valves
• Motor fill valves
• M&S (O-rings, lead gaskets, bolts) 

3.3 PREPARATION FOR INSTALLATION ON THE WELLSITE 

Preparation for installation on the wellsite :

• Check equipment delivered for installation.

NOTE :

Check Serial Numbers and equipment description of all ESP sections with those in request. 

3.4 ESP INSTALLATION  

ESP installation procedure is detailed in a previous post in this blog.

• All ESP assembling process must be done in accordance with the istallation prcoedures provided
• ESP Installation Checklist
• Installation Procedures For Drain and Fill Valves And Plugs 
• Proper O-Ring Installation on Motor Potheads

3.5 LOWERING ESP INTO THE WELL

3.6 ESP START UP PREPARATION 

4. ESP OPERATION 

4.1 ESP START UP AND PUTTING WELL INTO PRODUCTION 

1.  Start up procedure 
2. Determining Rotation 

4.2 SAFE OPERATION PROCEDURES 

Well start ups can be performed by specially trained and qualified personnel only. These personnel should have passed all required exams for working with electricity. 

Power  and  submersible  cables  connection/disconnection  works,  VSD  motor  service  and electrical measurements can be conducted by field service personnel who have appropriate training and certification. After measuring insulation resistance of the “cable-motor” system, the residual charge should be removed from every cable phase.Submersible cable connection must be done with switched off VSD. 

4.3 COMMISSIONING 

Practice recommendations :

•  While commissioning, it is advisable to consider if it is the first ESP after fracturing, ESP’s runlife and failure reasons for previous ESPs. If there were MLE melting, R=0 (cable or motor) so presumably the failure reason might be prolonged running without cooling or underload, i.e. running without flow rate. 
• If  ESP  is  not  equipped  with  DMT,  measure  well  dynamic  level  changes  every  15 min  in  case  if formation didn’t start producing; otherwise every 1 hour. Annulus pressure increase can be caused by indirect index of formation production, as it depends on dynamic level and is stipulated for the fluid degassing speed in the annulus.  
• All measurements like fluid level, pressure, current and frequency changes should be entered into the output  card.  If  previous  ESP  dismantling  showed  the  appearance of  mechanical  impurities  or  shaft section can’t rotate or move freely, then start up should be done with the minimum limited frequency of 37Hz. While doing this do not forget to control in accordance of the head characteristic with dynamic level; rise up frequency if needed (not more than for 1-2Hz). 
• Take  fluid  samples  to  identify  mechanical  impurities  build  up,  all  next  –  every other  day.  It  is undesirable to measure rate during first day of running to eliminate mechanical impurities inflow to gaging machine.  
• Recommended  commissioning  period  is  7  days.  This  period  will  allow  for mechanical  impurities flowback to decrease. 

The well can be determined as a stable if :

• Well dynamic level doesn’t change within an hour ± 50mins; 
• Well rate measurements fits pump head characteristic; 
• Flow rate is stable 

4.4 COMPLICATIONS DURING COMMISSIONING 

In case if VSD stops due to overloading (display shows “Overcurrent” sign) and cannot be started right after, next try to start must be not earlier than 30 min (if tubing check valve is leaking it is possible to have a backspin on the ESP).  

Flush method can be determined based on ESP or tubing check valve absence, circulation presence. Activate “Rocking start” regime, it will let accomplish of inching start up to free motor shaft or the pump. Set the value of kicks during start up, frequency for rocking start and rocking start method.  

During  start  up  VSD  motor  produces  kicks  with  direction  rotation  changing,  after several  kicks  it  tries  to accelerate  motor  to  the  operating  frequency  linearly.  Rocking start  methods  differs  by  character  and  kicks interchange. After 3-4 unsuccessful attempts to start up with direct rotation it is recommended to change initial rotation  direction  of  the  motor,  repeat  all  steps,  control  current  loadings  using display, “Bristol”  plotter deviations, measure with current tongs at the transformer output if needed. Period between start ups must be more than 15 minutes. Check insulation after several attempts to start up, so the equipment will be in safe mode.

 In case of ESP rocking start procedure don’t stop the VSD, change motor rotation direction (if the ESP turned on the reverse rotation), switch off the rocking start regime and let it run, controlling current loadings.  Motor operating current must stay limited under initial value.  

4.5 EXPLOITATION OF WELLS EQUIPPED WITH ESP’s WITH VARIABLE SPEED DRIVE (VSD) 

Exploitation of wells equipped with ESP’s with variable speed drive can gain in following :

• To make a decision about the further well production optimization beyond RIH with bigger ESP size (if running ESP on the maximum frequency doesn’t let to exploit full well potential). 
• To sustain work capacity of submersible equipment. 
• It  is  necessary  to  consider  the  possibility  of  submersible  equipment  parameters  changes  while frequency increases.   
• Maximum well rate achievement beyond optimizing submersible equipment work; (Russian customer’s requirements) 

Limiting factors when frequency rises up are :

• Submersible motor power capacity – motor power changes linearly after frequency was increased, at the same time power that is used by pump changes cubically; and then the moment comes when motor cannot produce power enough for pump (current increases and stop due to overcurrent occurs).
• Submersible equipment shaft strength – shaft loading increases when frequency rises up (as the head, productivity  and  shaft  receptivity  moment    change)  and  if  the  submersible motor  was  chosen  with  a  large power capacity the risk of shaft break may occur, especially when there a lot of mechanical impurities come out (shimming effect).
• Pump setting depth – pump head increases quadratic after frequency was increased and there is a risk occurs that the head can become more than PSD and it will lead to stop due to underload (pump will swap out all the fluid till  pump intake and will switch to idle regime).

Limiting factors when frequency lowers down are: 

• Pump head  - pump head decreases quadratic after frequency was lowered down  and the moment can occur when pump power (pump head) will not be enough to lift fluid column from dynamic level and rate will be  broken up, ESP will stop due to underload. 

To make a decision to increase the frequency the well some criteria must be estimated :

• Maximum estimated current loadings for surface equipment
• Maximum possible loadings for main switch in transformer substation
• Using submersible gauge placed on ESP relative fluid column over pump intake (submersion depth) can be calculated as per formula :

Where :

Pgauge – gauge pressure value at the pump intake, atm

Pannulus – annulus pressure, atm

Poil – oil density; kg/m3 

• if there is no submersible gauge on ESP relative fluid column over pump intake can be calculated as per formula:

Where 

Lri – PSD, m

Hdyn – well dynamic level, m

• solids content in pumping fluids at high frequencies must stay under :

          - for ARZ ESP - 500 ml/l

          - for ES ESP - 100 ml/l 

• ESP operating regime with considered current characteristics must be stable (no current shoves showing pump stuck or gas influx). 
• ESP current loadings level must stay under set limit for overcurrent. For that case it is necessary to optimize output voltage on step-up transformer (to select optimum voltage, when current value is minimum). Transformer voltage must be calculated  based on voltage necessary for the motor and voltage losses in the cable line relative to PSD and voltage drop down compensation in the net

There are some technological phases while well optimization :

• Frequency increase – ESP running due to specific program set to increase operating frequency
• Well stabilizing – temporary stopping of frequency increase when the definite frequency is achieved to make control  measurements  (rate  and  mechanical  impurities  must  be  measured  in  the  period  of  non-stop  well production from 6 to 12 hours)
• Stabilization - frequency increase stop at the definite level when ESP performance becomes worse or when mechanical impurities flow back to return parameters to normal range
• Optimal regime – regime when rate and frequency are optimal
• Deviation – operating frequency reduction because of protection devices kick-out, dramatically worsening of 
• ESP performance or volley mechanical impurities flowback

Frequency increase example: 

Normal frequency increase – increase program - 2Hz per day

Application criteria :

• stable ESP running regime (current loadings are flat)
• intake pressure is more than 40atm 

Careful frequency increase - increase program 1 – 1,5 Hz per day; 

Application criteria : 

• satisfactory ESP running regime (current loadings ripple do not lead to ESP stop due to underload or overload)
• intake pressure is more than 40atm 

Fast frequency increase - increase program 1 Hz per 20mins – 1HZ per 60mins; 

Application criteria :

• this regime is used when it is needed fast to return ESP to operating frequency after current or planned ESP stops during stable running regime before stop (current loadings are flat)

4.6 ACTIONS OF PERSONNEL WHEN ESP IS SHUTDOWN WHILE RUNNING 

Recommendations based on experience of several oilfields :

Power supply switch off (planned or emergency) : 

• start up at frequency reached before ( it is admitted to lower the frequency to 10 Hz value)
• to check and to correct underload protection if needed
• in compliance with results make a decision to continue frequency increase or not

Overload in power supply substation : 

• start up ESP at the low frequency (it is admitted to lower the frequency to 10 Hz value) to maintain stable running without switches off
• to check and to correct underload protection if needed 
• check the loadings on power supply, agree the switch replacement is needed

Underload ( switch off due to underload protection kick out) :

• analyze the reason of loading reduction (dynamic level decrease, tubing leakage, frozen surface line, not enough head, shaft break up, etc.)
• start up problems removal
• start up ESP;- to check and to correct underload protection if needed
• take preventive measures for the further stable ESP running and to continue frequency increase

Overload (switch off due to overload kick out) :

ESP stops due to current increase more than a set limit (stop due to overload) may occur due to the following : 

• high resistance to rotation in ESP pump (abrasive contamination, salt precipitation, etc.)
• not enough motor power or power supply power
• not optimal voltage selection on power supply transformer
• cable isolation damage

When ESP stops due to overload the personnel must :

• determine  time  and  operating  frequency  when  the  stop  occurred(  to  determine what  a  start  up frequency must be and what an operating frequency must be; after start up and frequency increase it is not recommended to increase previous ESP frequency for more than 2-3Hz till stability or overloading reasons removing)
• wait till fluid column is discharged from tubing (tubing dynamic level rises up, turbine ESP rotation stops)
• perform not more than 3 attempts to start up ESP at the frequency of 10Hz less  that achieved on manual regime on different regimes of rocking start with in-between start up periods not less than 30 mins (to cool down the engine) 
• measure insulation of “cable-motor” system; 
• if insulation is ok, start up ESP with at least one cistern of oil circulation after full drainage , creating excess pressure in annulus to ease ESP start up. Number of unsuccessful starts up must stay under 3 with in-between start up periods not less than 10 mins (to cool down the motor )
• if  ESP  startup  went  successfully  let  it  run  at the  start  frequency  to  stabilize  mechanical  impurities flowback (1-5 days), continue to increase frequency afterwards in “careful regime”. 

4.7 ESP PERFORMANCE CONTROL 

When operating ESP production shop shall 3 times a month check up operating parameters: dynamic level, production, buffer, linear and annulus pressures, insulation resistance, check valve function. Operating currency and voltage shall be checked up on a daily basis.  At low dynamic level (especially in winter when Sputniks do not provide measurements) it is obligatory to pressure test tubing with closed valve, register pressure build-up time and enter results in ESP passport.  

Under engineering supervision adjust VSD (make sure valve is closed) and enter corresponding information in ESP service passport  when operation mode is changed, and when dynamic level is close to the ESP rated head value. Water cut sampling shall be performed on a monthly basis and solid particles content and six-component test shall be provided when necessary. Acquired information shall be promptly entered in ESP passport. 

When necessary and in compliance with specific schedule a well shall undergo treatment jobs to eliminate wax scaling, salt and mechanical impurities followed by a corresponding entry in ESP passport. After long down time (exceeding 10 days) put well to production providing dynamic level measurement and stop monitoring ESP performance only after bringing well to stable production. 

To control ESP performance and to react in time for all changes in ESP runlife process it is recommended to regularly check active working wells (more than ones in tree month) and to measure all current parameters of ESPs. 

4.8 ESP FAILURE, PULLING AND DISMANTLE OPERATIONS 

4.9 EQUIPMENT RERUN