Gs lift and ESP Optimization

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Gas Lift Optimization
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Gas Lift Optimization

• Optimum production by gas lift is a stable rate
  as a consequence of a specific gas injection rate
  which leads to a production sustained for a
  longer time.
• Generally, the optimal amount of gas injection is
  determined by well tests, the rate of injection
  is varied, and corresponding liquid production is
  measured.
• Another way to optimize the gas lift injection
  rate to attain optimum profitability is using the
  Gas Lift Performance Curve, attained from
  Prosper, the method is defined as
• Selecting 4 points on the curve performance
• Draw tangents to each point
• Generate the slopes
• The slopes are plotted vs gas injection rate

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Gas Lift Optimization
The slope of the plot, is defined as M M
Cg/FoP Cg Gas lift cost, /MMscf Fo Oil
cut P Profit/barrel, /bbl
Plot of Gas Lift Performance Curve
Plot of Slope against Gas Injected, MMscf/day
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Gas Lift Optimization
Always is it good to validate the optimum gas
injection volume with well tests
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Gas Lift Troubleshooting
Field Techniques for Troubleshooting a Gas Lift
Well The main issue in gas lift injection is the
point of injection The technique more suitable
for a particular well must be carefully defined
to avoid unnecessary expenses and/or risk Most
common tests Communication Tests Define holes,
damaged check valves, unseated valves, leaking
completion packers, or annulus-tubing
communication
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Gas Lift Troubleshooting

• Troubleshooting steps
• There are three main areas where gas lift
  problems may occur
• Inlet (Surface)
• Outlet (Surface)
• Downhole
• First, analyze surface
• Gauges should be calibrated

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Gas Lift Troubleshooting

• Inlet problems
• Excessive Gas Usage
• Casing pressure
• Over injection
• Tubing or collar leak
• Cut or washed out lift valve
• Choke sizing
• Faulty gauges (WH casing or tubing pressures)

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Gas Lift Troubleshooting

• Inlet problems
• High casing pressure
• Gas injection volume
• Partially plug valves
• Flowing temperature
• Higher tubing pressure
• Restriction in the tubing

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Gas Lift Troubleshooting

• Inlet problems
• Low gas usage
• Confirm gas volume injection meter
• Verify operating temperature of gas lift valve
• Test injection/flow choke

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Gas Lift Troubleshooting

• 2. Outlet problems High back pressure is an
  indicator of a problem with the outlet
• Restriction through choke, debris or choke body
• Paraffin or scale build-up in the flowline
• Flowlines 90 degree turns or elbows
• Separator operating pressure
• Valve restrictions should be fully open and
  properly designed. Smashed flowline (road
  crossing places)

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Gas Lift Troubleshooting

• 2. Downhole problems more difficult to identify,
  only approach is to interpret the information and
  find out
• Well blowing gas dry
• Casing pressure exceeding the design operating
  pressure
• Tubing communication
• Lift point (verify with echometer or survey)
• Verify inflow from formation (if possible)
• If upper valves are operation properly, then the
  issue is below

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Gas Lift Troubleshooting

• 2. Downhole problems more difficult to identify,
  only approach is to interpret the information and
  find out
• Well will not take input gas
• Frozen choke or closed input gas valve
• Closed wing valves on the outlet side
• Feed problems
• If temperature is a problem, the well will
  produce periodically
• Verify the valve set pressures are not too high
  for the available casing pressure

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Gas Lift Troubleshooting

• 2. Downhole problems
• Well flowing in heads
• Too much or too little injection
• Port size of valves too large (pressure valves),
  limited feed from the reservoir
• Temperature interference (higher than expected
  volume at the beginning). With cooled valves,
  they will open again

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Gas Lift Troubleshooting
2. Downhole problems

• Well will not unload
• fluid column heavier than available lift
  pressure, or designed fluid weight lighter than
  actual weight
• WH backpressure is too high
• Valve staying open (sediments in the valves,
  salt)

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Gas Lift Troubleshooting
2. Downhole problems

• Hole in tubing. Test equalize tubing pressure
  and casing pressure by closing the sing valve.
• Low casing pressure and tubing pressure when
  closing the wing valve with the gas injection on

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Gas Lift Troubleshooting

• 2. Downhole problems
• Valve spacing too wide
• If a high pressure well is nearby, use it to
  unload the well or use N2.
• If the problem is severe, re-space the valves. A
  pack off gas lift is required, or shoot the
  tubing to get a new point of injection

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Gas Lift Troubleshooting

• 3. Tuning the well
• Unloading the well requires more gas volume
  injection than when operating
• Often, the input gas volume can be reduced once
  the point of injection has been reached
• Start the well on small input choke like 8/64,
  then increase the choke by 1/64 increments until
  the maximum fluid rate is achieved. Allow the
  well to stabilize for 24 hours after each change
  before another adjustment.

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Gas Lift Troubleshooting
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Gas Lift Design examples

• Determine the optimum GLR given conditions
• Unlimited amount of gas available,
• Given amount of gas (limited)

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Gas Lift Design examples
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ESP Design
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ESP non-Standard Conditions
ESP system for Conventional applications (Single
fluid, no gas production) Non-optimum conditions
for the pump may affect adversely the efficiency
of this type of artificial lift system. The
solution to those new conditions Introduction of
novel equipment or Modified procedures.
Production of Viscous Fluids The advantage of
the production of heavy oils with ESP units is
the low bubble point pressure of this type of
fluids and so there no free gas at the pump
suction. So the use of the ESP system in this
environment is a favorable approach.
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ESP non-Standard Conditions

• Main effects of the increased viscosity of the
  produced fluid
• Rapid pump capacity decrease
• Decreased head development by the pump
• Increased power to drive the pump
• Reduced pump efficiency
• If viscosity is not considered when selecting the
  equipment, the ESP unit would be extremely
  overloaded
• Each pump manufacturer has their own developed
  correction methods

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ESP non-Standard Conditions
Low Rate Pumps ESPs are designed for high or
extremely high liquid rates, but low-volume
applications are posible to compete with Sucker
ros pumping units In this scenario, ESP system
is posible due to the development on two
áreas Pump stage design and housing strength
improvement Also, deep pump setting led to
modify the pump housing to increase their burst
pressure properties. Those modifications allowed
production at low rate between 150 and 650 bpd,
from more than 10,000 ft deep wells.
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ESP non-Standard Conditions
Production of Gassy Wells Free gas cannot
produce the same pressure increase as the liquids
due to the much lower density of the gas phase.
Free gas will lead to Fluctuation of pump
output (surging). Cyclic changes in motor
load Finally the control system shuts down the
ESP unit. In sum, specific solutions like
non-standard installation types, gas separators
have to be considered when producing gassy fluids
with ESP systems.
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ESP non-Standard Conditions
Pump Performance Criteria (gassy wells) The
limits of stable pump operation can be evaluated
based on the calculation of those parameters
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ESP non-Standard Conditions
Pump Performance Criteria (gassy wells)
The gas void fraction is the percentage of free
gas in the total fluid As seen in the plot, the
amount of free gas handled by the pump increases
with increasing suction pressure, PIP
Turpin Correlation
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ESP non-Standard Conditions
Solutions (gassy wells) Pump set below
perforations velocity of downward velocity lower
than gas rising velocity (0.5 ft/s), Annulus size
should allow this separation. Requires a rathole
or sump in the well. Any drawback???? High
temperature motors are required! Use of motor
shroud it acts as reverse-flow separator by
changing the flow direction, and directs the flow
along the ESP motor for cooling effects.
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ESP Solutions gassy wells

• Required a low fluid velocity (ideal less than
  0.5 ft/s) so gas bubbles may rise through the
  casing annulus.
• Another option is a dip tube, connected to the
  bottom of the regular shroud the benefits are
• Improved natural gas separation
• Production from a restricted area where the ESP
  would not pass
• Possible to use in horizontal sections (dip tube
  reaching into the horizontal section)

ESP with open-ended shroud
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ESP Solutions gassy wells
Inverted Shroud fixed below the pump intake
(reverse flow gas separator)

• Rotary Gas Separators, high speed spinning
  separates the fluids due to differences in
  density.
• A cross-over device directs
• Gas into the casing annulus for Venting to the
  surface and 2. liquid to the pump intake
• And there are much more options..

ESP with Inverted shroud
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ESP Production of Abrasive Solids

• It is expected the produced fluids to carry
  solids, which will produce abrasion/erosion of
  the moving parts of the pump (particularly
  impellers), leading to catastrophic failure of
  the pump.
• Solid-laden fluids production requires special
  technical solutions and sophisticated materials.
  Sand is the most critical problem due to the
  common occurance along with well fluids. Sand
  production facts
• Usually starts at high rate wells (prime choice
  for ESP systems)
• Water breakthrough accelerates the process
• Increases with changes in flow rate

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ESP Production of Abrasive Solids

• It is expected the produced fluids with solids,
  (abrasion/erosion of the moving parts)
  impellers.
• Sand is the most critical problem due to the
  common occurance along with well fluids. Sand
  production facts
• Usually starts at high rate wells (prime choice
  for ESP systems)
• Water breakthrough accelerates the process
• Increases with changes in flow rate

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ESP Production of Abrasive Solids
Afected áreas in the ESP unit and
Solutions Erosion Impellers and diffusers.
Minimized with special metals (Ni-Resist, alloy
with 18 nickel) or hard surface coatings on
critical areas Axial wear in thrust bearings
and upthrust/downthrust washers. Use tungsten
carbide or ceramics (usually zirconia) in main
thrust bearings Radial abrasion the most
significant sand damage effect in ESP units. Some
solutions Use rubbber (diffuser bore),
hardening of wearing surfaces with tungsten
carbide (expensive), silicon carbide, or
ceramics, they are very brittle though.