Open Hole and Cased Hole Petrophysical Inputs for Carbon Capture Projects

Some of the key petrophysical inputs required for carbon capture projects that will be discussed in the class include:

Porosity:

Porosity measures the volume of pore space within a rock or sediment. It is essential to understand the porosity of the reservoir as it determines the capacity to store CO2. High porosity indicates more storage potential. Open hole tools are discussed in detail as well as cased hole sonic and pulsed neutron logs for older wells without openhole logs.

Permeability:

Permeability measures the ability of a rock to transmit fluids (like CO2) through its pore spaces. A reservoir with high permeability allows for better CO2 injection and distribution within the formation. Techniques are discussed to calibrate log derived permeability-thickness with well test data. Well test quality control is covered as well to ensure that the calibration values are correct. Core based permeability is discussed as well with corrections for irreducible water saturation and relative permeability to the phases involved.

Formation Thickness:

The thickness of the geological formation is important because it impacts the overall storage capacity. A thicker formation typically has more storage potential. The Stiles-George net permeable thickness method is discussed where core data is used to provide a statistical relationship between porosity and permeability that honors the core permeability and porosity distribution. This method is particularly useful in carbonates where regression analysis is often limited due to poor correlation coefficients. It is the preferred method for sandstones as well since it honors the core permeability data distribution for the specific reservoirs involved. It addresses the issue that for a given porosity there are often two or three orders of magnitude difference among core perms for that porosity value.

Lithology:

Understanding the composition and mineralogy of the rock formation is crucial. Certain lithologies, such as sandstone or limestone, are more suitable for CO2 storage due to their porosity and permeability. Pulsed neutron logs are discussed for this as well to provide both openhole and cased hole detailed lithology information.

Caprock Integrity:

It’s essential to assess the thickness and integrity of the caprock to ensure the containment of the stored CO2. Log based estimates are covered along with detailed DFIT procedures to calibrate the log based in-situ stress distribution.

Wellbore Integrity:

Cement evaluation is covered in detail to discuss the options available with sonic and ultrasonic tools. Pulsed neutron water flow logging is discussed as well to detect flow behind casing. Electromagnetic casing thickness surveys are discussed along with the latest version of ultrasonic casing thickness and integrity evaluation (i.e Dark Vision and EV systems).

Depth and Pressure:

The depth at which the reservoir is located and the initial reservoir pressure are important factors. Deeper formations and higher initial pressures can increase storage security. Both DFITs and wireline pressure measurement tools are discussed in detail.

Temperature:

Temperature affects the behavior of CO2, especially in supercritical conditions. It can influence CO2 density and viscosity, impacting its storage characteristics. Temperature logging is discussed as well to supplement the other log suites and for input into the rock mechanics models.

Salinity and Brine Properties:

The chemical composition of the formation’s brine can affect the reactions between CO2 and minerals in the reservoir. Understanding brine properties helps assess the potential for mineral trapping of CO2. Emphasis is placed on salinity estimation from the SP log as many of these wells will be in areas where water samples are not available. The Rwa method is discussed as well for zones that are clearly water bearing.

Rock Mechanical Properties:

These include parameters like rock strength, elasticity, and stress. These properties are important for assessing the mechanical stability of the reservoir and the potential for induced seismicity during CO2 injection. Calibration of these properties to DFIT data is covered as was discussed above. Information required for thermal stress alteration calculations is discussed as well.

Well Data:

Information about existing wells, including their locations, depths, and conditions, is crucial for planning CO2 injection and monitoring.

Geological Modeling:

Advanced geological modeling techniques are often used to integrate all of these petrophysical inputs and create a detailed representation of the subsurface, helping to predict CO2 behavior and migration.

Monitoring Infrastructure:

In addition to initial inputs, ongoing monitoring tools such as pressure gauges, temperature sensors, and seismic monitoring may be used to track the movement and behavior of injected CO2 over time. Pulsed neutron surveillance logging and fiber optic sensors are discussed in detail.
 
These petrophysical inputs are critical for assessing the feasibility and safety of carbon capture and storage (CCS) projects and for ensuring the long-term containment of captured CO2 in geological formations. Proper characterization and ongoing monitoring are essential to minimize the risk of leakage and environmental impact.
 
Local case studies are encouraged to apply the techniques.