Guidance for Subsea CCS Systems

Guiding the development of safe and reliable subsea CCS systems for permanent CO₂ storage

Subsea CCS projects are still in their early stages, with industry standards and regulations for their design currently developing across many regions.

These resources are intended to help the industry evaluate key decisions and mitigate risks unique to a subsea CCS system. While leveraging existing knowledge from the subsea oil and gas industry, it specifically addresses the unique aspects of subsea CO₂ injection systems.
The aim is to enable the development of safe, reliable, and cost-efficient designs to support global emissions reduction goals. It also seeks to encourage consistency in regulatory requirements and align operators and suppliers on core functionalities for fit-for-purpose and cost-effective equipment.

Why Subsea CCS Requires Specific Guidance

Subsea CCS presents distinct challenges compared to traditional offshore hydrocarbon operations. The primary function is long-term storage of CO₂, which involves different risks and operational requirements. While existing hydrocarbon barrier requirements are often considered valid, there are opportunities for simplification in some areas and new risks specific to subsea CCS. Key differences include:

The complex phase behaviour of CO₂ (gas, liquid, dense, supercritical, two-phase) and the impact of impurities on temperature, pressure, and material compatibility.

The potential for extreme low temperatures due to CO₂ depressurization or Joule-Thomson cooling.

The risks associated with residual water and the formation of carbonic acid or hydrates.

Project-specific considerations for components like Downhole Safety Valves (DHSVs) and the potential to modify or remove the tree cross-over valve.

The need for well integrity not just during injection but also throughout the post-injection monitoring period.

The potential for reservoir pressure to increase over time, unlike typical hydrocarbon depletion.

Challenges and increased risks associated with testing barrier or isolation elements.

The significant risk of water ingress when internal pressure in the system is lower than the external hydrostatic pressure, which can lead to corrosion and hydrate formation.

Specific considerations for subsea intervention, including safe venting procedures and managing CO₂ phase changes.

The potential for more frequent cycling of valves and chokes due to variable injection rates

Get the reports

Design guidance for subsea carbon capture and storage systems

Provides guidance to designers and developers of carbon capture and storage (CCS) systems with all, or portions, of the system located underwater.

Report includes

Subsea CCS projects overview

Subsea systems design

Subsea architecture

Equipment functional requirements

Appendices

Glossary

Get the report now

What the Guidance Covers (Click for details)

What This Guidance Covers

IOGP Report 665 “Design guidance for subsea carbon capture and storage systems”, provides comprehensive guidance for the design and development of subsea CCS systems.

The Report covers:

Subsea CCS Project Overview
It outlines the drivers, assumptions, and decision factors for selecting subsea CCS over onshore or platform-based alternatives, including safety, storage capacity, and environmental considerations.

Subsea Systems Design
The report presents high-level system configurations such as pipeline injection from shore, intermittent or continuous injection from vessels, and hybrid models, along with reservoir types and injection strategies.

Subsea Architecture
It discusses well placement, monitoring wells, infield layout, tie-back distances, and control system considerations, with emphasis on flexibility, expansion, and integration with marine activities.

Operational Considerations and Flow Assurance
This includes thermodynamic behaviour of CO₂, impurity management, hydrate and corrosion risks, startup/shutdown procedures, and intervention strategies.

Barrier Philosophy and Isolation
The report defines well and system barrier requirements, testing protocols, and isolation strategies to prevent CO₂ leakage and seawater ingress, referencing standards like API and NORSOK.

Equipment Functional Requirements
It provides guidance on trees, manifolds, jumpers, pipelines, risers, and control systems, including material selection, temperature and pressure tolerances, and qualification standards.

Reuse of Equipment
The document includes criteria for repurposing existing pipelines, risers, manifolds, and control systems for CCS applications, with emphasis on integrity assessment and regulatory compliance.

Installation, Commissioning, and Intervention
It offers practical guidance for dewatering, startup, shutdown, and intervention operations, highlighting CCS-specific risks such as Joule-Thomson cooling and hydrate formation.

Subsea Barrier and Isolation Philosophy for CCS Systems

Building on IOGP Report 665, this report provides additional detailed guidance for subsea CCS developments on subsea isolation and barrier design philosophy.

Report includes

Term definitions

General philosophy description

Primary and secondary well barrier testing of CO₂ systems

Subsea CCS barrier overview

Preventing leakage from injection flow path to environment

Appendices

Get the report now

What the Guidance Covers (Click for details)

What This Guidance Covers

IOGP Report 665-1 – Subsea Barrier and Isolation Philosophy for CCS Systems builds on IOGP Report 665 – Design guidance for subsea carbon capture and storage systems. Report 665-1 provides additional detailed guidance for subsea CCS developments on subsea isolation and barrier design philosophy. The reader is expected to have a thorough understanding and familiarity with IOGP Report 665.

Barrier and Isolation Philosophy
It defines the general principles of two-barrier systems, including passive, active, and temporary barriers, and explains how these apply differently in CCS compared to hydrocarbon systems.

Well Barrier Testing for CO₂ Systems
It details testing strategies for primary and secondary well barriers, including challenges unique to CO₂ systems such as phase changes during depressurization and the implications for leak testing.

Subsea CCS Barrier Overview
This includes well barriers, tree system barriers, and upstream barriers like Pipeline End Manifolds (PLEMs), spare hubs, and field expansion hubs, with diagrams and lifecycle considerations.

Leakage Prevention Strategies
The report provides detailed guidance on preventing leakage from the injection flow path to the environment, annulus, and service lines during installation, injection, and intervention operations.

Tree System and Downhole Safety Valve (DHSV) Options
It evaluates different DHSV configurations (e.g., SCSSV, injection valves, storm chokes) and their suitability based on reservoir pressure and operational risk.

Project-Specific Design Considerations
It highlights how CCS-specific risks (e.g., CO₂ phase behaviour, temperature cycling, material compatibility) influence design decisions, including the use of cross-over valves and annulus management.

HAZID Process and Risk Assessment
The document includes a Hazard Identification (HAZID) template used to evaluate risks across different reservoir types and operational scenarios, supporting tailored barrier design

Industry Standards and References
It builds on IOGP Report 665 and references key standards like API, NORSOK and others to align CCS barrier design with established hydrocarbon practices while addressing CCS-specific needs.