Topic 3: Real-World Leakage Assessment

Gulf Coast Carbon Center 2018-2022 Aspirational Multi-Year “Big” Plan

Problem statement
Theoretical and fieldwork to assess the risk of leakage from carbon storage reservoirs has been well developed, but a short-fall in critical assessment of leakage models for correctness and completeness and sparse real-world validation can cause inadequate or miss-targeted monitoring. In particular, the mechanisms, rates, processes, and reactivity of fluid transport through non-reservoir rocks has been considered only simply. To prepare for either a leakage incident or a leakage allegation, realistic experience with the possible leakage scenarios is needed.

Goals

1. To improve the conceptualization of the migration mechanisms by which out-of-zone leakage and leakage to atmosphere or groundwater can occur. Examples are:

Determining what flux rate of leakage is significant to storage security and what is detectable.
Determining the importance of, and ways in which, leakage flux be separated from background flux for more accurate accounting. Considering operational and site closure timeframes as well as extended time frame permanence.
Determining the factors that most affect reactivity and interaction of fluids with rock, the factors that change the fluid chemical and physical properties, and understanding flow path, and the temporal characteristics of leakage
- Determine the realistic properties and geometries of various types of pathways through overburden including where fluids will migrate in focused pathways, where fluids will accumulate prior to spilling or exceeding capillary entry pressure, and how saturation may evolve. We will also seek to better understand when and where the leakage is vertical as opposed to when and where risk is dominated by horizontal migration.
Resolve how multiphase fluid flow mechanisms impact fluid-fluid and fluid-rock interactions. This goal will incorporate improving the combination of multiphase flow and geochemical reaction beyond flash calculations.
Determining which geologic variables play dominant controls on leakage and the methods for identifying these variables for any specific site.

2. Assess implications of migration mechanisms Focus on above-zone but also includes some work inzone) for detection to improve monitoring, for example via:

Better targeting of detection strategy
Quantifying and predicting the attenuation and retardation of leakage, including predicting how these processes will affect the use of tracers (natural and introduced) for leakage assessment.
Improved understanding and prediction of signal to noise (e.g. seismic sensitivity to leakage)
Improved strategies for quantification of leakage across all points of surface emission.

3. Implications of migration mechanisms for environmental impact and remediation, for example, diffuse versus focused leakage and/or variations in flux rate and environmental impact.

Methods
We propose a broad spectrum of interconnected studies including numerical models, physical models and experiments, and potentially field experiments to accomplish these goals. Examples are:

Apply pore scale models to assess directional relative permeability
Use head-gas sampling for monitoring the bottom hole liquids
Validate Invasion Percolation/Darcy simulators to assesses saturation resulting from different migration mechanisms through various geologic fabrics and architectures
Use image analysis for quantification of flow through models
Apply physical and numerical models of flow paths to consider various geometries, including low dips and trapping at various scales (e.g., from bedform to regional)
Develop numerical and laboratory methods of assessing processes, timing and rates of dissolution of CO₂ in two-phase and possible multi-phase settings in porous media and wellbore.
Assess the degree to which petroleum systems can be used as a proxy for site characterization and/or leakage detection. One example is to use GoMCarb project to understand the implications for storage security in areas with low hydrocarbon accumulations such as Chandeleur Sound. We will also evaluate concepts of fluid inclusion stratigraphy using data derived from well cuttings to evaluate regional and local seal quality.

Four-year target accomplishments

Improve recognition of significant leakage, thereby increasing confidence in methods for identification of sites and conditions that are unlikely to leak
Improve risk assessment in terms of more realistic likelihood and impact
Develop a more effective monitoring framework including better-defined strategies for lowering monitoring cost. Improved leakage conceptualization will also provide for more targeted leakage assessment with respect to when, where and how to look for leakage. Such an approach will, therefore, improve our ability to both 1) state with more confidence that leakage has not occurred and, 2) should leakage occur, this approach will improve our ability to locate, attribute and quantify leakage. Better leakage assessment will also help prepare for staged integration of monitoring in different zones (link to topic 5)

Go to Topic 2: Preparing for Large Volume Storage – BIGFOOT

Go to Topic 4: The U in CCUS

Last Updated: June 25, 2019