Exploration Risk Assessment for Storage in the Operate stage

Objective

• Containment risk management. Monitoring CO₂ behaviour over the long-term (i.e. geochemical changes, CO₂ migration path, sub-surface gravity changes, etc.). Evaluating the effects of pressure changes on geomechanical stability
• Implementing updates or improvements to Monitoring, Measurement and Verification (MMV) techniques as project matures
• Mitigation of the effects of exceptional events / plant failure

Major Deliverables

This stage continues the re-iterative process of acquiring, collating and performing a series of risk analyses on the MMV data, using an appropriate risk analysis tool. The primary objectives are to manage containment risks, or in the event of an exceptional event occurring, to implement an appropriate mitigation strategy. Deliverables should include:

• Regular (annual?) MMV assessment reports for delivery to all stakeholders (i.e. regulatory authorities and public) detailing the outcome of qualitative and quantitative risk-based studies for the selected site (i.e. probabilistic, deterministic and hybrid). These should be based on the initial risk assessment and continually updated with new results from ongoing studies and the most recent MMV and equipment maintenance data to inform and update the risk register, including results from:
  • Computer simulations of CO₂migration and dissolution within the storage site complex such as history-matched plume development, saturation profiles, pressure build-up simulations and forecasts of future plume distribution. Any significant deviations from expected behaviour should be highlighted for more detailed investigation, since these may indicate the presence of:
    • Modelling errors resulting from failure to capture significant geological heterogeneities and / or use of inappropriate modelling parameters (e.g. relative permeability / fluid saturation / interfacial tension / capillary pressure data), further propagating uncertainties from one or both areas
    • Monitoring errors resulting from equipment bias or poor calibration / processing / interpretation procedures
• Storage reservoir pressure and temperature data analyses (plots, tables, etc.), highlighting the significance of any trends (e.g. likelihood of CO₂ phase / density changes and / or  multi-phase flow occurring within any part of the storage site, impacts on storage efficiency, etc.)
• Coupled reservoir / geomechanical models to confirm site is meeting agreed performance targets (i.e. optimum injection rates / pressures). These models should also provide risk-related information on thermal fracturing potential, fracture pressures / gradients, etc.
• Coupled geochemical / geomechanical models to evaluate the effects of combined processes on formation / caprock integrity
• An inventory analysis (plots, tables, etc.) of CO₂ injected and hydrocarbons and / or water produced (by mass / volume), including any CO₂ vented to atmosphere. If a multi-layer plume has developed, this could also include estimates of mass / volume contained within each layer, individual layer column heights and graphs indicating flux rates into particularly high risk layers (e.g. structurally highest layer underlying caprock)
• Any changes required to the MMV plan, risk register or injection / production strategy as a result of containment risk or storage efficiency changes (e.g. sudden loss of injectivity, pressure increase or migration into an area not covered by existing MMV equipment) and an assessment of the costs likely to be incurred as a result of any such changes (e.g. need to drill additional injection wells or perform well intervention)
• Hydrogeological models to evaluate the displacement of pore fluids by CO₂ / hydrocarbons, test for the presence of an "active" aquifer and assess the consequences of any migration forcing (e.g. do computer simulations of the plume over time match the observed MMV data or is there a lateral shift along a particular direction that cannot be explained by topography alone?)
• Surface flexural deformation models (primarily for terrestrial sites), designed to capture rates of uplift / subsidence and provide stress field data
• Well pressure integrity measurements (if such MMV data is available) to demonstrate compliance to regulatory authority and / or identify wells that may require intervention and remediation
• Any maintenance, calibration and intervention activities performed on MMV equipment, wells and / or the storage reservoir, including the results of (re-) calibration tests, integrity tests and outcome of remediation operations
• Any requirement for additional data, studies, experimental work or testing to address any new risks or uncertainties highlighted by current evaluations (e.g. poor injectivity results due to high salinity, high microbial / heavy metal concentration in formation fluids, etc.)
• Contingency plans for responding to containment loss issues or unpredicted migration into subsurface zones identified as high risk (e.g. close proximity to hydrocarbon production area, poorly-completed legacy wells, geological formation with connection to seabed / surface, etc.). These may be developed and refined through the application of systematic risk analysis techniques such as the Bow-Tie Method (DNV CO2QUALSTORE, 2010)
• Schedule risk analysis for all co-ordinated activities, including fall-back position in the event of non-compliance (e.g. inability to acquire high quality seismic survey data due to unfavourable weather, etc.)
• Updated risk management plan, with initial risks upgraded or downgraded as required and any new risks identified from new information / data / simulations incorporated into the risk register, including any impact hypothesis and contingency measures associated with their inclusion
• Environmental / social report detailing any issues arising during the operations phase (e.g. environmental pollution, liability claims, public protests, etc.) and describing how these issues were dealt with in a risk context (i.e. were these problems predicted by the initial risk analysis, was there a strategy in place, was it appropriate and was it implemented correctly?), including recommendations for future improvement
• Financial summary covering aspects of economic risk encountered during the operations phase (e.g. financial losses due to equipment failure, accidents, delays, compensation payments, etc.)

Tasks

The main tasks during this stage will involve developing and refining a portfolio of monitoring and contingency plans based on  detailed, risk-based assessments of MMV data acquired during operations and any modelling data, results and recommendations derived from ongoing studies. The Bow-Tie Method (DNV CO2QUALSTORE, 2010), provides a useful technique for assessing ongoing risks, capturing consequences arising from these risks and developing preventative or corrective contingency measures.

Generic Bow-Tie Risk Analysis Methodology (DNV CO2QUALSTORE, 2010)

Two major risk elements need to be addressed during the operations stage:

• Conformance loss - this means that the storage site is failing to meet the required performance criteria (e.g. loss of injectivity, unexpected phase changes and loss of storage efficiency, etc.) - not a critical risk in regulatory terms, but still significant due to inability to meet project objectives and liability issues that may arise as a result of this failure
• Containment loss - a critical risk (or top event) in regulatory terms and one which has to be addressed through a detailed bow-tie analysis

As the bow-tie diagram illustrates, safeguards may be:

• Preventative / passive (e.g. natural or engineered barriers identified prior to injection operations, reduction of injection pressure, etc.)
• Corrective / active (e.g. reservoir and / or well intervention and remediation performed during operations in response to a threat)

An example bow-tie analysis is presented below (modified from Shell Canada, 2010). Top seal breach is identified as the top event, consequences of this event are listed down the right-hand side of the diagram and likelihood of threats associated with this event are listed down the left-hand side. Risk of containment loss is mitigated by reducing likelihood of threat and / or consequences. Barriers are identified by preventative / passive (light blue) and corrective / active (dark blue), thus risk reduction is achieved through a combination of both MMV activities and provision of suitable passive and / or active control measures.

In addition to this type of graphical output, these preventative / corrective measures should also be documented, with a detailed description of the activities required and how these measures will be implemented (e.g. methodology, duration, environmental impact, etc.).

Example Bow-Tie Risk Analysis For Top Seal Compromise (modified from Shell Canada, 2010)

Using this type of assessment methodology (or a similar methodology), operators should be able to satisfy the regulatory authority that:

• The existing MMV set-up is fit for purpose
• Any threats and consequences arising from these threats have been captured by the analysis process
• Preventative and / or corrective safeguards have been developed to deal with critical threats and can be implemented as required
• The storage site continues to meet or exceed agreed performance targets and statutory requirements

Aside from this re-iterative risk assessment process, other related tasks will be ongoing during the operations stage, such as:

• Developing and refining simulation models to improve history-matching and forecasting
• Long-term experimental work and results reporting
• Research and field trials associated with the development of improved methods for Measurement, Monitoring and Verification (MMV)
• Ongoing development and documentation of the processes / controls / strategies currently in place to manage identified and evaluated risks, including intervention and remediation programs for the:
  • Overburden
  • Existing and CO₂ injection well/s
  • Storage reservoir/s
  • Identifying and documenting any areas of uncertainty for further study (e.g. there may still be some uncertainties from a residual risk perspective over remediation techniques and their effectiveness or permanence if they have never been field-trialled previously)
  • Providing an outline financial breakdown of perceived risks to inform the project management process
  • Setting deadlines for any outstanding studies / actions that still need to be addressed
  • Adjusting MMV plans in accordance with performance behaviour (e.g. it may be possible to reduce the level of MMV required over time if the site exceeds agreed performance requirements approaching the closure stage; alternatively, if the site underperforms or encounters problems, it may be necessary to increase the level of MMV to counteract the increasing level of risk)
  • Continuing to engage with the stakeholders and regulatory authority on risk management issues and ensure a smooth transition into the operational phase of the project

Examples

• Shell Canada Ltd., MMV Plan (example application of Bow-Tie risk assessment methodology)
• CO₂ Capture Project, Vol. 2 Chapter 33: Risk Assessment Methodology for CO₂ Storage: The Scenario Approach (Note: requires users to register for download)
• National Energy Technology Laboratory / US Department of Energy, Best Practices for: Risk Analysis and Simulation for Geologic Storage of CO2 (Version 1, March 2011)
• Det Norske Veritas, Managing Risk - Can CO₂ Storage Site Qualification Help My Project Meet a 2015 Deadline?
• Det Norske Veritas, CO2QUALSTORE Workbook with examples of applications - examples and case studies of risk analysis through the storage site life cycle
• OSPAR Convention for the Protection of the Marine Environment of the North-East Atlantic,  OSPAR Guidelines for Risk Assessment and Management of Storage of CO2 Streams in Geological Formations - assessment process, characterisation and management
• Lawrence Berkeley National Laboratory, Assessment of Risks from Storage of CO₂ in Deep Underground Formations
• Det Norske Veritas, CO2WELLS - Guideline for the risk management of existing wells at CO₂ geological storage sites
• Det Norske Veritas, CO2QUALSTORE - Guideline for Selection and Qualification of Sites and Projects for Geological Storage of CO₂
• Korre et al.,(2009), Modelling the uncertainty and risks associated with the design and life cycle of CO₂ storage in coalbed reservoirs
• Wildenberg et al. (2007), Long-Term Safety Assessment of CO₂ Storage: The Scenario Approach
• Shell International Renewables, Risk Management for CCS and CO₂ Policy (including FEP methodology)
• The IEA Greenhouse Gas R&D Program, Geological Storage: Risk Assessment and Monitoring - presentation by David White, Schlumberger Carbon Services
• IEAGHG/Quintessa, CO₂ FEP Database - includes risk assessment activities during all stages of a CCS project (requires registration to access)
• EU Geocapacity, Assessing European Capacity for Geological Storage of Carbon Dioxide
• The Leading Edge, CO₂ Sequestration Monitoring and Verification Technologies Applied at Krechba, Algeria (Mathieson et al., 2010)
• Energy Procedia, Evaluation of Risk assessment Methodologies Using the In Salah CO₂ Storage Project as a Case History (Dodds et al. 2010)
• Energy Procedia, Probabilistic Approach to Evaluating Seismicity in CO₂ Storage Risk Assessment (Ayash et al., 2009)
• 10th International Probabilistic Safety Assessment & Management Conference, Seattle, CO₂ Geological Storage Safety Assessment: Methodological Developments (Bouc et al., 2010)

Key Personnel

Expert panel of risk assessment specialists and / or professional representatives from the following technical, economic, environmental, legal and HSE disciplines:

• *Chairperson and Steering Committee
• Management representatives from the project developer
• Senior representatives from the regulatory authority and local / regional government
• Geologists / Geophysicists / Geochemists
• Geomechanical / Geotechnical Engineers
• Petroleum/Reservoir / Drilling Engineers
• Environmental Consultants
• Legal Practitioners (Liability, Property and Mineral/Oil/Gas/CCS)
• Financial/Economic/Political Analysts
• Risk Assessment / Safety / Insurance Analysts (HSE)

* In some cases, multi-discipline experts may be available (e.g. geology/geophysics), who may be particularly suitable for these roles.