Capture Ready: Fast-Track Your CCS Site Evaluations

By: Tariq Siddiqui

A quick site screening helps narrow down potential CO2 injection sites early in capture-ready projects. This article focuses on the technical and geological aspects of CO2 site screening. For an overview of the required data, refer to our previous article on best practices and tips for CO2 storage project screening.

SCREENING BASIS

CO2 storage sites must be evaluated based on three technical criteria:

1. Capacity: Adequate storage capacity for injected CO2.

2. Injectivity: Sufficient injectivity for CO2.

3. Containment: Effective barriers to contain CO2.

EVALUATION CRITERIA

Each parameter is ranked from 1 (very poor) to 5 (excellent).

Capacity

1. Porosity:

- < 5%:     Rank-1

- 10-20%: Rank-3

- > 20%:   Rank-5

2. Net Thickness

- < 10 m:   Rank-1

- 20-30 m: Rank-3

- > 50 m:   Rank-5

3. Net-to-Gross (NtG): Higher NtG is preferred.

4. Minimum Total Capacity:

- 20 Mt for a single commercial site (1.0 mtpa for 20 years).

- 100+ Mt for hub and cluster developments.

Injectivity

1. Permeability:

- < 1-10 mD:  Rank-1

- 10-100 mD: Rank-3

- > 100 mD:   Rank-5 (caution: high permeability can make CO2 too mobile).

2. Minimum Annual Injectivity:

- < 1 mtpa: Non-commercial or small commercial projects.

- 1.0-2.0 mtpa: Commercial, single CCS projects.

- > 5.0 mtpa: Commercial hub and cluster developments.

Containment

1. Regional Seal: Extensive seal/barrier required.

2. Injection Depth: Sufficient depth (around 800 meters) to maintain CO2 in supercritical conditions.

3. Initial Pore Pressure: Below fracturing pressure to avoid accidental fracturing.

4. Stress Barrier:

- < 5 bar:   Rank-1

- 5-10 bar: Rank-3

- > 15 bar: Rank-5

5. Faults: Preferably free of large-scale faults; use 2D-3D seismic data to identify potential CO2 leakage pathways.

Other Technical Parameters

1. Salinity:

A salinity of < 2000 ppm is generally considered a potable aquifer. A high salinity ( > 10,000 ppm ) is also not suitable as solubility of CO2 in aquifers decrease with salinity ( Always check your local guideline for potable aquifer salinity).

- < 2000 ppm:          Rank-1

- 2000-8000 ppm:    Rank-3

- 8000-10,000 ppm: Rank-5

2. Legacy Wells: The number and condition of legacy wells affect leakage risks and site evaluation.  A remote CO2 injection site with no legacy well data may pose challenge to regional evaluation and calibration and project team may end drilling Strat or appraisal wells. On the other hand too many wells may pose potential leakage risk for the injected CO2, especially if the legacy wells had poor cementing.

Non-Technical Parameters

Non-geological factors, such as site suitability, social, and regulatory parameters, are also part of site screening. These will be discussed in future articles. Common Risk Segment (CRS) maps help identify the best potential injection sites.