eni s.p.a.upstream & technical services
2013-2014 Master in Petroleum Engineering and Operations
Well Unloading Technologies and Selection Criteria
Author: Agozie Amadi Prince
San Donato Milanese 13-14-15 October 2014
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Stage SubjectWell Unloading Technologies and Selection
Criteria
San Donato Milanese 13-14-15 October 2014
Author
Agozie Amadi Prince
Division eni S.p.A.
Upstream & Technical Services
Dept. TEOP
Company Tutors
Elisa di Biase
Salvatore Privitera
University Tutor
Prof. Francesca Verga
Master in Petr.Engineering & Operations 2013-2014
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� Project Scope
� Theoretical concepts
� Well Unloading Technologies description
� Well Unloading Selection Criteria
� Conclusions
List of Content
Stage SubjectWell Unloading Technologies and Selection
Criteria
eni s.p.a. upstream & technical
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Project Scope
� Main activities for the scope� Physical mechanisms literature review� Technologies evaluation and comparison� Selection guidelines
� Industrial Impact and Expected BenefitsEnsure the gas production and extend the life of wells affected by liquid accumulation
� Current technology statusIndustry is using different methods in order to mitigate the liquid loading effects (i.e. foamer, velocity string, wellhead compressor, plunger)
� Technical Motivation
Manage the liquid accumulation (water and/or condensate) in
order to ensure the gas production
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� Project Scope
� Theoretical concepts
� Well Unloading Technologies description
� Well Unloading Selection Criteria
� Conclusions
List of Content
Stage SubjectWell Unloading Technologies and Selection
Criteria
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Theoretical conceptsWhat is liquid loading
A well is suffering from liquid loading when its gas production rate has fallensharply off its intended decline curve and remains there due to theaccumulation of water or condensate at bottom of the wellbore
Drawbacks
� Unexpected mechanical stress (slug flow)
� Corrosion
� Early well abandonment
� Production decrease
� Revenue falling
� Cost rising
ITALY TOTAL RECOVERED PRODUCTION ~ 500 kSm3/day (3.2 kboed, 100 k€/d)
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Theoretical conceptsIdentification of liquid loading
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Diagnostic actions
� Water sources
� Associated Water
� Water Produced from Another Zone
� Aquifer water
� Casing leak
� Water coning
� Condensate sources
� Retrograde condensation
How to identify liquid loading
Theoretical models
Monitoring actions
Critical velocityWell performance analysis
Production parameters analysis Well history review
P/T surveysSurface / Downhole samplingOther investigations (i.e. Logs)
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� Project Scope
� Theoretical concepts
� Well Unloading Technologies description
� Well Unloading Selection Criteria
� Conclusions
8
List of Content
Stage SubjectWell Unloading Technologies and Selection
Criteria
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� Artificially Liquid Lifting
Well Unloading Technologies description
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� Foamer Applications
� Velocity String
� Wellhead Compression
� Downhole pumps (rod, PCP, ESP)
� Reducing surface tension between gas & liquid, and also the liquid density
� Increasing gas velocity by reducing the tubing flowing section
� Increasing gas velocity by reducing wellhead pressure
� Intermittent production � Cycles of re-pressurizations
� Plunger lift
Techniques applied by eni
Gas wells Unloading techniques Worldwide
� Gas lift � Reducing liquid density
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Well Unloading Technologies descriptionFoamer applications
Foam preferentially adsorbs at the interface, lowering the surface tension between fluids (liquid and gas) and liquid density
+ foamer
CONS
� Cheap to apply
� Tolerance of particulates
� Versatile for different completions and environments
PROS
� Surfactant used may cause emulsion problems
� Wells with higher condensate may not foam well.
( )2
1
g
41
gL4
1
gρ
ρρσ1.92V
−=
Turner equation
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Well Unloading Technologies descriptionFoamer selection & treatments
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� Fluid compositions
� WCR
� Specific gravity
� Reservoir conditions (P&T)
� Lab tests
� Reactivity (height of foam)
� Foam Stability (Half-time)
� Compatibility with fluids
� Compatibility with treating equipment
� Foam breaker (Defoamer selection)
Foamer selection Injection treatments
� Dropping soap sticks down the tubing
� Batch treatments
� Continuous Injection via Capillary String
� Continuous Injection via Production annulus
� Combined treatments
Capillary injection
Batch injection
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Well Unloading Technologies descriptionVelocity string
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Velocity string can be defined as the installation of a wellbore tubular (usually from 1” to 3-1/2” in diameter) to modify the hydraulic characterization of an existing completion tubing
Evaluation of the best tubing size by Well Performance
Analysis in order to:
� Maximize velocity (v > vT)
� Minimize pressure losses
� CT velocity string
� Through tbg. installation
� Tubing replacement
� Higher velocities for a given rate
� Medium-long term solution
� Good in tight gas reservoir
PROS CONS
� Requires special tools
� High costs
� Further loading will be more severe than original
2 3/8” ODNo Loading, low frictions
1 11/16” ODNo Loading, high
frictions
2 7/8” ODLoading, low frictions
OPTIMUM SOLUTION
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Well Unloading Technologies descriptionWellhead Compressor
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Used to lower the wellhead pressure to increase gas velocity, even lower than flowline back pressure
CONS
� Reduction of the THP and BHP (drawdown increase)
� Increasing & stabilization of production rate
� Wide operating range
PROS� Surface modifications needed
� Maximum liquid production to be tolerated
� Not compatible with solid production and corrosive fluids
� Not suggested for low productivity wells
Sensitivities on
WHP reduction to define
� WHC characteristics (type, size)
� Energy needed
� Surface modifications
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Well Unloading Technologies descriptionPlunger lift
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Plunger lift system is an intermittent lift method that uses only theenergy of the reservoir to produce the liquids.
M O TO R IZ EDVA L VE
E LE CTR O N ICC O N TR O LLE R
LU B R ICA T O R
FL O W TEEW /O -RI NG
B LE ED
VA L VE
C A TC H E RW /A R R IV A LSE N S O R
EX T ER N ALC A B LE
M A ST ERVA L VE
B U MP ER SP R IN G
PLU N G ER
B YP A S SVA L VE
TU B IN G STO P
Conventional Continuous
� It is a rig-less operation
� Cheap to apply & maintain
� Requires no outside energy source
PROS
CONS
� Not efficient in solid production wells
� Limited by GLR, cannot work in low GLR wells
� Not efficient in highly deviated and horizontal well
M O TO R IZ EDVA L VE
E LE CTR O N ICC O N TR O LLE R
LU B R I CA T O R
FL O W TEEW / O -RI NG
B L E E D
V A L V E
C A TC H E RW /AR R IV A LSE N S O R
E X T E RN ALC A B LE
M AS T E RVA L VE
B U MP ER SP R IN G
PL UN G ER
B YP A S SVA L VE
TU B I N G STO P
or
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¼” OD Capillary injection
Well Unloading Technologies descriptionFoamers application Case histories (water)
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Benefit duration = 1 yr
Cost ~ 80 k€Total Income ~ 1000 k€
POT = 1 month
Batch injectionPRE POST
Gas rate (kSm3/d) 5 15
Liq rate (m3/d) 0.1 0.4
PRE POST
Gas rate (kSm3/d) 0 25
Liq rate (m3/d) 0 0.6
Benefit duration = 2.5 yrs
Cost ~ 250 k€Total Income ~ 6000 k€
POT = 1 month
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Well Unloading Technologies descriptionWellhead Compressor Case Histories (water)
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10 installations in Italy since 2013
PRE POST
Gas rate (kSm3/d) 5* 18
Liq rate (m3/d) 0.8 1.5
* Cyclic production
Benefit duration = 1.5 yr (on going)
Cost ~ 300 k€Total Income (till now) ~ 1600 k€
POT = 2.5 month
Well A
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Well Unloading Technologies descriptionPlunger lift case histories (condensates)
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M O TO R IZEDVA LVE
E LE CTR O N ICC O N TR O LL E R
LU B R ICA T O R
FL O W TEEW /O -RI NG
B LE ED
VA L VE
C A TC HE RW /A R R IV A LSE N S OR
EX T ER N ALC A B LE
M A ST ERVA L VE
B U MP ER SP R ING
PLU N GE R
B YP A S SVA L VE
TU B IN G STO P
PRE POST
Gas rate (kSm3/d) 1 2.5
Liq rate (m3/d) 4 6
Benefit duration = 1 yr
Cost ~ 75 k€Total Income ~ 390 k€
POT = 2 months
Well APlunger lift Installed
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� Project Scope
� Theoretical concepts
� Well Unloading Technologies description
� Well Unloading Selection Criteria
� Conclusions
18
List of Content
Stage SubjectWell Unloading Technologies and Selection
Criteria
eni s.p.a. upstream & technical
services
Well Unloading selection criteria
19
Technical Evaluation
EconomicEvaluation
FINAL SELECTION
Constraints� HSE
� Logistic issues
� Authorizations
CAPEX, OPEXIncome, POT, ROI
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Well Unloading selection criteriaTechnical evaluation matrix
Velocity String Plunger LiftWellhead
CompressionFoamer Batch
Foamer
via Capillary
No corrosive fluids
Actual tubing > 2 3/8" OD
Deviation < 3°/100ft
Uniform Tubing size
No solid production
Gas rate < 350kScf/d
GLR ≥ 400 Scf/bbl/1000ft
Liquid rate < 350bbl/d
No corrosive fluids
No solid production
Gas rate < 700-875kScf/d
Liquid rate < 20 bbl/d
(without surface
modifications)
No corrosive fluids
Deviation < 12°/100ft
GLR range: 1000-8000 scf/bbl
Liquid rate range: 5-100 bbl/d
GLR range: 1000-8000 scf/bbl
Liquid rate range: 5-100 bbl/d
No corrosive fluids
Only Water 2 1 2 1 2
Only Condensate 2 2 2 0 0
Water +
Condensate2 1 2 1 1
High Reservoir
Pressure4 1 2 2 3
Low Reservoir
Pressure0 3 4 2 3
Low Permeability 3 1 1 1 1
High Reservoir
temperature2 1 2 1 1
Deep well (>
10,000 ft)3 3 3 1 2
Large Tubing 4 2 3 1 2
Small Tubing 0 2 4 2 3
Restrictions in
tubing2 1 3 2 3
3 1 1 4 2
sporadic continuous continuous none regular
Technical constaints
Liquid type
Reservoir
Parameters
Well/Completion
Parameters
Ranking
factors
ManagementMaintenance
frequency
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Well Unloading selection criteriaEconomic evaluation table
Cost = average CAPEX + OPEX for Italy
* Gas price assumed equal to 0.17 €/Sm3
Low cost Short-term benefit
High cost Long-term benefit
Approach
Cost, k€
Typical Benefit
duration,
monthsDelta prod
5 kSm3/d
Delta prod
15
kSm3/d
Delta prod
5 kSm3/d
Delta prod
15 kSm3/d
Delta prod
5 kSm3/d
Delta prod
15 kSm3/d
Batch 80 6 3.1 1.0 153 459 1.9 5.7
Capillary String 250 36 9.8 3.3 918 2754 3.7 11.0
Plunger 100 24 3.9 1.3 612 1836 6.1 18.4
WHC 300 48 11.8 3.9 1224 3672 4.1 12.2
POT (months) Income (k€) ROI
Velocity string not included; cost varies depending on the installation operation
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� Project Scope
� Theoretical concepts
� Well Unloading Technologies description
� Well Unloading Selection Criteria
� Conclusions
List of Content
Stage SubjectWell Unloading Technologies and Selection
Criteria
eni s.p.a. upstream & technical
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� HSE and Logistics constraints have to be always taken into accountduring the selection process
� A proper understanding of the liquid accumulation problem and itsimpact is fundamental to design the most suitable unloadingtechnique
� The most suitable unloading technique to be applied must bechosen after proper technical and economic evaluations
Conclusions
� Nowadays, gas well loading impactis becoming more and moreimportant when dealing withmature & depleted gas fields
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Acknowledgements
I would thank eni for permission to present this work
and related results and TEOP colleagues for the
technical support and needed assistance.
San Donato Milanese 13-14-15 October 2014