Design for optimal treatment of produced water Design for
optimal treatment of produced water33rd rdInternational Seminar on
Oilfield Water ManagementInternational Seminar on Oilfield Water
Management Rio de Janeiro, 7Rio de Janeiro, 7 -- 9 June 2010 9 June
2010Anne Finborud, Mator AS Anne Finborud, Mator ASDesign for
optimal treatmentDesign for optimal treatment what does it mean?
what does it mean? Flexible regards to increasing produced water
flow rate during field lifetime, both total flow rate and flow rate
from individual separators. Robust regards to higher than expected
amount of water from low pressure separators.R b d d i fi l l h
hifi d id ib i Robust regards to production of particles although
specified in a design basis as not expected. Robust regards to
treatment and routing of already separated streams (rejects)
toRobust regards to treatment and routing of already separated
streams (rejects) to minimize negative effects. Flexible regards to
utilization of the pressure and temperature balance in the t
system. Robust regards to account for the total oily water system
including open drain, closed drain and jetting water. closed drain
and jetting water. Flexible to handle future low pressure
production. Robust regards to a control philosophy with increased
focus on constant flowRobust regards to a control philosophy with
increased focus on constant flow instead of constant
interfaces.Input data for design and equipment selection Input data
for design and equipment selection? Characteristics and thereby
treatability of produced water prior to treatment depends on: the
type of fluid to be producedthe specification, design and operation
of the separation trainthe production chemicals used the production
chemicals used Having knowledge about factors such as droplet
break-up, coalescence, physical and chemical properties, effects
from process components etc. related to your specificyapplication,
greatly increases the possibility for making good design
solutions.Input data for design and equipment selection (contd)
Input data for design and equipment selection (contd)System
information: Field frame conditionsProcess information: Pressure
Gas/condensate, oil, heavy oil Production profilesS ti t iPressure
Pressure drop choke valves Temperatures Separation train Product
spec Production chemicals Gas lift / high GLR Slugging Well
workoversFluid properties: Oil and water densitites Solids
Separator design Oil and water densitites Oil and water viscosities
Oil/water interfacial tension Water phase salinity TAN WAT WAT
OiW-concentration Oil droplet sizesHigher number of factors having
negative influence on produced water requires a more robust
process.Conventional technologies for oily water treatment
Conventional technologies for oily water treatmentClass of
technology Type of technologyDriving force General area of
applicationMain technology Hydrocyclone Enhancedgravity Oilfields
with high/low water flow, high/lowgy(Primary and secondary
treatment)y y g y g , gOiW.Degasser Dissolvedflotation/gravityAll
fields with high/low water flow, low OiW.Flotationunit
Inducedflotation/gravity All fields with high/low water flow, low
OiW.Compact flotation unitInducedflotation/gravity All fields with
high/low water flow, low/medium OiW.Centrifuge Enhancedgravity
Gas/condensate fields and open drain. Low water flow and high/low
OiW.Enhancing/polishingtechnologyExtraction unit(e.g.
CTour)Coalescence/extraction Oilfields with high/low water flow
with available condensate. Special attentiondissolved
technology(Tertiary treatment)(e.g. CTour) condensate. Special
attention dissolved components.Extraction unit(e.g.
MPPE)Coalescence/extraction All fields with low water flow, low
OiW, and low solids and scale potential. Special attention di l d t
dissolved components.Coalescing unit(e.g. MaresTail,
PectF)Coalescence Oilfields (with hydrocyclones), and with low
solids and scale potential.)Filters(e.g. CrudeSorb, TORR,
nutshell)Coalescence/extraction Gas/condensate fields with low
water flow, low OiW, and low solids and scale potential.Examples:
treatment of oilfield produced water Examples: treatment of
oilfield produced waterHow to combine the technologies into an
overall system? How to combine the technologies into an overall
system?Oily water and sand treatment philosophy Oily water and sand
treatment philosophy Best Available Techniques (BAT), with built-in
robustness against operational variations. PWRI applications
require treatment PWRI applications require treatment. Two
treatment stages to meet World Bank discharge limit of 29 mg/l oil
in PW. Three treatment stages to meet stricter project
requirements. g p j qThis also to apply for treatment of PW from
2nd stage/3rd stage/coalescer. Separate out PW from the oil train
as early as feasible / possible. Avoid direct recycling of reject
streams and skimmed oil streams as this may impair oil/water
separation over time. Reject streams should be treated in a reject
treatment stage with: Skimming of the oil phase for routing to
export or last stage separator/coalescer Skimming of the oil phase
for routing to export or last stage separator/coalescer. Treatment
of the water phase in the PW system with possibility for recycling
for increased flexibility.Or rejects should be routed to a slop
system with dedicated treatment system. For pumping of PW prior to
treatment use screw pumps (mono) or low speed centrifugal pumps. PW
systems benefit from having constant flow rates. Include
possibility for cleaning in place (CIP).Oily water and sand
treatment philosophy (contd) Oily water and sand treatment
philosophy (contd) When PW is used as jetting water it shall be
taken downstream of the final treatment stage. Use sand cyclones on
jetting water return. Water overflow to be returned to the PW
system. Sand underflow to be treated according to sand management
strategy Sand underflow to be treated according to sand management
strategy. Online oil in water measurement is a valuable tool for
optimization and troubleshooting. Cl d d i l Closed drain vessel:
To be separate from the reject treatment stage. Skimming of the oil
phase for routing to export or last stage separator/coalescer.
Treatment of the water phase in the PW system with possibility for
recycling for increased flexibility.Or closed drain should be
routed to a slop system with dedicated treatment system.Od i Open
drain: Skimming of the oil phase for routing to export or last
stage separator/coalescer. Water from non-hazardous open drain can
be discharged directly to sea. Water from hazardous open drain can
be injected, sent onshore or discharged to sea after dedicated
treatment.Oily water and sand treatment philosophy (contd) Oily
water and sand treatment philosophy (contd)Case: produced water
pump Case: produced water pump Screw pumps are far more gentle to
the oil droplets thang phigh speed centrifugal pumps, thereby more
suitable as produced water pumps. For centrifugal pumps increasing
dP increases droplet break-upScrew pumps do notbreak up. Screw
pumps do not show such correlation. Case: low pressure produced
water Case: low pressure produced water Low pressure produced water
is often more stabilised by particles and chemicals (lower
interfacial tension thereby lower oil droplet coalescence), thereby
more difficult to treat difficult to treat. However, treatment
systems for low pressure water are often less equipped than high
pressure water low pressure water has negative influence on the
discharge.Case: sand cycloneCase: sand cyclone Oil content200u/s
sand cycloneSolids content1200u/s sand cyclone140160180d/s sand
cycloned/s hydro cycloned/s flash tank80090010001100d/s sand
cycloned/s hydro cycloned/s flash tank80100120Oil,
[mg/l]500600700Solids, [mg/l]20406010020030040002 min 7 min 20 min
BaselineTime f r om st ar tjet t ing01002 min 7 min 20 min
BaselineTime f r om st ar tjet t ing Solids d/s sand cyclone little
affected by solids u/s sand cyclone, i.e. high solid content at the
start of jetting is effectively removed by the sand cyclone. Solids
and oil d/s hydrocyclone and degasser are somewhat higher during
jetting, and lowest at baseline one day after jetting. Case:
cleaning in place (CIP) Case: cleaning in place (CIP)Before CIP:
After CIP:Case: recycling of rejects Case: recycling of rejects
Rejects are often a mix of oil, particles and chemicals. Direct
recycling of rejects to the separation train may impair oil/water
separation. Many installations experience accumulation of
rag-layers in the separators with resulting need for frequent
carry-over procedures, and close follow-up of unforeseen process
up-sets over time both on the oil and produced water side. p p p
Negative effects from direct recycling of rejects occur over time,
and are difficult to prove by short time testing. However, we
strongly believe that alternative solutions than direct recycling
of rejects in many cases would make a large difference especially
on unforeseen and difficult to explain increased discharge of oil
in water to sea. Case: recycling of rejects (contd) Case: recycling
of rejects (contd) Direct recycling of rejects via the 57-tank high
OiW and particles to 3stage separator Direct recycling of rejects
via the 57-tank high OiW and particles to 3. stage separator.
Results in bad quality water from 3. stage separator, however,
better than the stream from the 57-tank. Intermittent return
directly to the degasser, i.e. treated by only one treatment stage.
Large negative influence on discharge to sea.Case: recycling of
rejects (contd) Case: recycling of rejects (contd)Online OiW:
Build-up of rag-layer in coalescer and intermittent (on/off) return
of bad quality watere e (o /o ) e u o bad qua y a ewith flocculant
and particles to 1. stage separator.P i d i hlf fl li j i Periods
with control of flocculant injection, reduced skimming from
degasser thereby reduced recycle, and improved pumping freq
encofater ret rn from coalescer to frequency of water return from
coalescer to1. stage separator.Case: recycling of rejects (contd)
Case: recycling of rejects (contd) Reject water phase treated by
dedicated centrifuge. Discharge < 10 ppm OiW with clean
centrifuge requires CIP and optimized continuous operation
optimized continuous operation. Recycling of water phase from
closed drain has some negative effect on water from the
separatorhowevereasy manageable byseparator, however, easy
manageable by the hydrocyclones and degasser. Improved solution for
reject treatment! All produced water discharge problems solved...?
All produced water discharge problems solved...?Thank you! Thank
you!