www.baker-rds.com

M. J. Haigh

Well Design DifferentiatorsCO2 Sequestration in Depleted Reservoirs

SPE 124274

Presented at Offshore Europe 2009 Conference and Exhibition

“Towards a Low Carbon Future”

www.baker-rds.com

Introduction

• Why is this subject important?

– Limited CCS well design knowledge available

– CCS to play key part in O&G future

• Feasibility study

– Depleted gas reservoir

• Other sources

– Specialist service companies

www.baker-rds.com

Objectives

• Review environment of a CO2 injection well

• Identify main well design issues and hazards

• Evaluate and assess the impact

• Propose potential solutions

• Key areas:

– Injection Operations

– Well Integrity

www.baker-rds.com

Project Management

• Technical workgroups

– Capacity

– Integrity

– Injectivity

• Identified areas of integration

• Provided practical project

framework

Capacity

InjectivityIntegrity

www.baker-rds.com

Injection Operations

• Challenges during Injection:

– Establishing design constraints

– Review the effects of low wellhead

temperatures

– Accurately predicting CO2 phase

transition behaviour

– Reduced perforating efficiency in

depleted reservoirs

CorrosiveMixtures

IntegrityConcerns

ExplosiveDecompression

TemperatureFluctuations

www.baker-rds.com

Design Constraints

• CCS developing concept

– New projects will consist of demonstrator schemes

– Late life cycle: Full base load injection

• Specific project requirements

– Initial gaseous ramp up stage

• Power generation companies

– Project management disconnect

• Fit for purpose injection strategy

required

www.baker-rds.com

Low Wellhead Temperatures

• Temperature drop across choke

– Potential hydrates at tree valves

– Integrity issues

• Valves

• Tubing hanger seals

• Dehydrate flow stream

• Evaluate risk of hydrate

CoolingEffect

HydratesForming

IntegrityConcerns

www.baker-rds.com

CO2 Phase Transition Behaviour

• Demonstrator scheme

– Gas phase injection / liquid phase injection

• Gas phase injection

– Reservoir pressure increases

– THIP increased to maintain injectivity

– Critical pressure reached

• Liquid phase injection

– Reservoir pressure continues

to increase

www.baker-rds.com

CO2 Phase Transition Behaviour

• Phase transition

– Unstable phase behaviour

• What we think could happen:

– Fluid density increases

– Injection rate increases

– Depressurisation of wellbore

• Mitigation strategy:

– Maintain single phase in wellbore

– Velocity reducing insert string

– Modification of THIP

www.baker-rds.com

CO2 Phase Envelope

0

200

400

600

800

1000

1200

1400

1600

1800

2000

-50 -40 -30 -20 -10 0 10 20 30 40 50

Temperature (˚C)

Pre

ssu

re (

psi)

100 v% CO2

Gas Injection - Initial

Gas Injection - Mid

Gas Injection - Final

LiquidPhase

SupercriticalRegion

C

GasPhase

TransitionRegion

Increasing Pr

www.baker-rds.com

Injection Strategy

Increasing Reservoir Pressure / Time

Gas

Well 4

Well 1

Well 2

Well 3

Well 1

Well 4

Well 3

Well 2

Well 2

Well 1

Well 4

Well 3

Well 1

Well 2

Well 3

Well 4

Liq

uid

Inc. THIP

Inje

ction L

ife C

ycle

Retr

ofit In

sert

Str

ings

Liq

uid

Liq

uid

Inc. THIP

Inc. THIP

Inc. THIPActive Injection Duty

Offline Obs. / Cont. Duty

www.baker-rds.com

Injection Strategy Benefits

• Avoids phase transition uncertainty

– Single phase flow in wellbore

• Simple architecture

– Flexibility from gas to liquid phase injection (stages overlap)

• Reduced hydrate risk downhole

• Well duty: Injection and observation

– Increased sink integrity (less penetrations)

• Reduced project CAPEX

www.baker-rds.com

Perforating Efficiency

• Cased and cemented

– Best for long term hydraulic isolation

• Reduced perforation efficiency

– Conventional static underbalance not possible

• Perforating options

– Extreme overbalance perforating

– Reservoir k > 100 mD

– Leak off rate below fracture pressure

• Reactive perforating

– Suitable for depleted reservoirs

PSI

www.baker-rds.com

Reactive Perforating

Normal crushed zone occurs

Exothermic reaction with pressure surge

Super-charged pressure surge removing damaged zone

Beneficial tip fracture

www.baker-rds.com

Material Selection

• Metallurgy selection subject to range of views

• Tubular materials options

– Carbon steel

– Glass reinforced epoxy (GRE) lined CS

– 13% Cr stainless steel

– CRA such as Duplex

• Specific corrosion assessment

– Water solubility in CO2

www.baker-rds.com

Water Solubility in CO2

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Pressure (psia)

Wat

er c

on

ten

t in

CO

2 f

luid

(p

pm

) 32 degF

43 degF

50 degF

PhaseBoundary

THIT 43 degFTHIP 580 psia

CO2 Solubility is 500 ppm

www.baker-rds.com

Well Integrity Workflow

WellCharacterisation

Leakage ScenarioWorkshop

DegradationModelling

MonitoringPlan

Remediation Options

Risk Assessment

www.baker-rds.com

Measurement and Monitoring

• In well monitoring

– Integrity risks

• Wellhead / packer feed through-ports

• Fibre optics selected

– Increased reliability and performance

– Integrity monitoring

– DTS

• Wellbore temperature correlation

• Injection profiling

www.baker-rds.com

Summary

• Technical workgroups

– Capacity, Integrity and Injectivity

• Key injectivity challenges

– Potential CO2 phase instability

• Maintain single phase

• Velocity insert string

• Reduced perforation efficiency

– Reactive perforating

• Well integrity

– Leakage scenario workshop