BY Tariq Siddiqui UEPA
INTEGRATING DATA IS A KEY
The successful deployment of Carbon Capture and Storage (CCS) technologies is critical to achieving a low-carbon economy. However, CCS projects face significant risks—particularly concerning subsurface conditions. Uncertainties surrounding reservoir characterization (e.g., storage capacity, integrity) and the potential for CO2 leakage can undermine investor and stakeholder confidence.
To mitigate these risks and ensure the economic viability of CCS ventures, it is essential to integrate comprehensive reservoir characterization, modeling, and subsurface testing during the early phases of project development. This proactive approach not only increases technical certainty but also aligns with broader business strategies, enhancing regulatory compliance and long-term profitability. In this article, we explore how subsurface characterization, modeling and monitoring/testing can reduce risks and provide valuable insights for strategic business decisions in CCS projects.
MANAGING RISKS IN CLASS VI WELL PERMITTING
The Environmental Protection Agency (EPA) Code of Federal Regulations (40 CFR 146.81 to 146.95) outlines 15 mandatory rules for Class VI injection well permitting for safe geologic sequestration of CO2 ensuring integrity of USDW. Among the most critical that are discussed here are:
Geologic Characterization (40 CFR 146.82 (a) (3)
Area of Review (AoR) and Corrective Action Plan (40 CFR 146.84)
Testing & Monitoring Plans (40 CFR 146.87; 40 CFR 146.90)
These elements form the heart of the Class VI well permitting process and are central to de-risking CCS projects. The following sections break down these requirements and explain how they contribute to the overall success of CCS ventures.
Geologic Characterization & Modeling-For Managing Risks & Uncertainties
Geologic characterization of reservoir and confining zones serves two main objectives:
Informing Technical and Commercial Aspectsof the project: This includes understanding capacity, injectivity, and containment of injected CO2.
Meeting EPA/UIC Regulatory Requirements: This is essential to managing subsurface uncertainties and risks.
The reservoir characterization is iterative and dialogue-driven process between project developers and EPA/UIC review team. Initially, project developers submit a permit application based on early-stage data in the Pre-Permitting phase (40 CFR 146.82 (a) (3). The EPA/UIC reviews the application for completeness and conducts a full technical review. Once the application meets all requirements, the permit is issued. During the Pre-Injection phase (40 CFR 146.87), further data collection and testing in injection well may lead to revised and final reservoir characterization, which is then compared to the initial characterization. If the two match, the injection of CO2 is authorized.
Reservoir characterization itself can be broken down into two phases:
General Characterization : De-Risking The Region:
Basin/regional and site-specific assessments.
Specific Characterization : De-Risking specific zones.:
Detailed focus on injection zones and confining zones.
Data gathered throughout this process helps demonstrate the suitability of the site according to the minimum criteria for siting under Class VI regulations (40 CFR 186.83).
Model Development Strategy - A Three-Step Process To Manage Risks
A 3D simulation model is critical for predicting CO2 injection performance and ensuring regulatory compliance and manging uncertainties and risks (40 CFR 146.84 (C) (1). This model integrates data from reservoir characterization in a three-step process:
Conceptual Site Model --> Physical Processes Modeled --> Site Computational Model
Conceptual Site Model
Physical Processes Modeled
Site Computational Model
Conceptual Site Model (CSM) - An Overview of the Project
Outlines key elements such as:
CO2 source, location and distance from the injection point.
Planned injection volume (e.g., 1.0 mtpa).
Injection stream composition (e.g., ~99% CO2).
Injection zone characteristics (e.g., depth, reservoir properties).
Potential risks, including legacy exploration and groundwater production well locations.
Physical Processes Modeled - Understanding The Physics
Project developers must decide which physical processes will be modeled, including:
Multiphase Flow:
Structural and stratigraphic trapping.
Hysteresis or capillary trapping
CO2 solubility in brine and variable fluid dynamics.
Thermal effects and flow behavior.
Reactive Transport:
CO2 precipitation, dissolution, and mineralization.
Geo-Mechanical Modeling:
Fault activation in injection and confining zones.
It is important to note that while multiphase flow modeling is required, reactive transport and geo-mechanical modeling are optional depending on site, and should be discussed with the EPA/UIC program director.
Site Computational Model - A Tool For Managing Subsurface Uncertainties
Once the conceptual model and key processes are defined, the next step is to develop the 3D site computational model. This involves:
Selecting the Right Code: Choose a simulator that can model the identified processes.
Defining Spatial Boundaries: Determine the extent and grid structure of the model.
Establishing Model Time Frame: Set the duration from the start of injection until pressure differentials dissipate or for a specified time period.
Parameterization: Populate the model with site-specific parameters, including formation permeability, porosity, and phase-partitioning coefficients.
Unceratinty analysis: Parametric study to identify parameters with most adverse impact on plume and pressure ront.
AoR and Corrective Action Plan - Tracking CO2 Plume & Remedial Actions
A 3D site-specific simulation model helps track the CO2 plume and pressure front throughout the lifecycle of the project. The plume is defined as segregated phase of CO2 (super-critical, liquid or gaseous phase) and pressure-front is the zone of elevated pressures due to CO2 injection where the differenial pressure between injection zone and USDW is higher than threshold pressure causing loss of integrity by migration of fluid due to presence of any hypothetical conduit (manmade Ex. wells or natural ; faults or fractures). The AoR is the total area under influence of the plume and pressure front.
The Area of Review (AoR) and Corrective Action Plan are critical for identifying areas where CO2 injection could pose risks (40 CFR 146.84), particularly if pressure differentials cause risk of CO2 migration into Underground Sources of Drinking Water (USDWs). In US, USDW have salinities < 10,000 mg/litre.
The boundaries of AoR are based on simulated prediction of the extent of the separate CO2 phase plume and elevated pressure-front. The AoR’s purpose is to delineate areas where CO2 plume and pressure-fronts could migrate and pose a contamination risk to USDWs (see cover Figure). The Corrective Action Plan focuses on AoR, identifying potential conduits (natural or man-made), assessing their integrity, and implementing corrective actions to prevent leaks. its done in three steps; identify wells penetrating injection zone in the AoR, evaluating its condition and performing remedial action if it lost its mechanical integrity
Testing & Monitoring Plans - Matching Performance with Prediction
Testing and monitoring are essential for protecting USDWs and ensuring ongoing regulatory compliance (40 CFR 146.82 (2) (8) & (a) (15) and commercial success of the CSS venture. These activities occur in two phases:
Pre-Injection Phase (40 CFR 146.87):
Conduct open-hole and cased logs.
Perform mechanical integrity tests (MIT) - 40 CFR 146.89
Estimate fracture pressures and assess hydrogeological characteristics.
Measure baseline Geochemical properties
During Injection Operations (40 CFR 146.90):
Monitor injection-phase parameters (Inection .rates, composition, volumes etc)
Track groundwater quality and geochemical changes.
Monitor plume and pressure front extension.
Perform ongoing mechanical integrity testing and pressure fall-off tests.
WAY FORWARD: INTEGRATION KEY FOR CCS SUCCESS
For a CCS project to succeed, technical insights from subsurface testing and modeling must be seamlessly integrated into broader business strategies. This integration enables data-driven decision-making, providing a clearer understanding of project feasibility, cost implications, and potential risks. By aligning technical rigor with business objectives, CCS developers can gain stakeholder confidence, enhance project efficiency, and ultimately achieve a financially viable, sustainable CCS venture
The UEPA : Navigating CCS Complexity for Client Success
For your next CCUS project, trust the expertise of UEPA. With our in-depth knowledge of CCS project development, we offer precise and efficient support for your project. Our comprehensive services cover the full lifecycle of project development and reservoir characterization, ensuring successful Class VI permit applications. Partner with UEPA to ensure your CCUS project is executed smoothly and sustainably.
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