M. J. Haigh Well Design Differentiators CO 2 Sequestration in Depleted Reservoirs SPE Presented at Offshore Europe 2009 Conference and Exhibition Towards a Low Carbon Future

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

Objectives Review environment of a CO 2 injection well Identify main well design issues and hazards Evaluate and assess the impact Propose potential solutions Key areas: –Injection Operations –Well Integrity

Project Management Technical workgroups –Capacity –Integrity –Injectivity Identified areas of integration Provided practical project framework

Injection Operations Challenges during Injection: –Establishing design constraints –Review the effects of low wellhead temperatures –Accurately predicting CO 2 phase transition behaviour –Reduced perforating efficiency in depleted reservoirs

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

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

CO 2 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

CO 2 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

CO 2 Phase Envelope

Injection Strategy

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

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

Reactive Perforating Normal crushed zone occurs Exothermic reaction with pressure surge Super-charged pressure surge removing damaged zone Beneficial tip fracture

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

Water Solubility in CO 2 Phase Boundary THIT 43 degF THIP 580 psia CO 2 Solubility is 500 ppm

Well Integrity Workflow Well Characterisation Leakage Scenario Workshop Degradation Modelling Monitoring Plan Remediation Options Risk Assessment

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

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