Reservoir characterization is a critical step in the process of carbon storage, as it helps determine the suitability and potential of a site for carbon dioxide (CO2) storage. Despite its importance, the process of reservoir characterization poses several challenges that must be addressed to ensure the successful and safe implementation of carbon storage.
Challenge 1: Lack of Subsurface Data
One of the main challenges of reservoir characterization is the lack of reliable subsurface data. In many cases, the data collected from wells and seismic surveys may be incomplete or inadequate for characterizing the subsurface. This lack of data makes it difficult to accurately determine the size, shape, and structure of the subsurface reservoirs, which is essential for safe and effective carbon storage.
Solution: Advanced Data Acquisition and Interpretation Techniques
To address this challenge, advanced data acquisition and interpretation techniques can be used to enhance the quality and accuracy of subsurface data. For example, the use of high-resolution seismic surveys and geophysical imaging can provide a detailed picture of the subsurface, allowing for an accurate assessment of the reservoirs. Additionally, the integration of multiple data sources, such as well logs, production data, and geomechanical data, continues to ensure accuracy of the subsurface characterization.
Challenge 2: Complex Subsurface Geometry
Another challenge in reservoir characterization is the complexity of subsurface geometries, particularly in heterogeneous and fractured reservoirs. This complexity can make it difficult to accurately predict the flow of CO2 in the subsurface, and the potential for migration and leakage.
Solution: Numerical simulation and modeling
Numerical simulation and modeling can be used to address this challenge by predicting the flow of CO2 in the subsurface. By using models that incorporate the complex subsurface geometries, it is possible to better understand the potential for migration and leakage, and make informed decisions on the suitability of a site for carbon storage.
Challenge 3: Uncertainty in Subsurface Parameters
Uncertainty in subsurface parameters, such as permeability and porosity, can also pose a challenge in reservoir characterization. These uncertainties can result in inaccurate predictions of the flow of CO2 in the subsurface, and the potential for migration and leakage.
Solution: Updating Subsurface Parameters
To address this challenge, it is necessary to continually update subsurface parameters as new data becomes available. For example, monitoring the injection of CO2 over time (4D seismic and timelapse gravity methods) can provide valuable information on the subsurface, allowing for the refinement of subsurface parameters to continually ensure accuracy of the characterization.
Challenge 4: Lack of Geologic Understanding
Similar to oil and gas exploration, CCUS projects demand in-depth understanding of the reservoirs. Key geologic challenges include a lack of knowledge of the structural geology, depositional environment, lithology, lateral vs. vertical reservoir continuity, facies changes, diagenesis, depth, pressure, and temperature of the formations.
Solution: Literature Research
Literature research is crucial in establishing a solid foundation. Literature research must follow a multiscale approach where subsurface structure and thickness maps are generated, trap mechanisms are fully understood, and depositional environment and lithology are modeled. Such models are then combined with reservoir properties such as diagenesis, porosity, permeability, temperature, and pressure to provide a full scope subsurface analysis.
Challenge 5: Subsurface Seal Quality
Understanding the quality of seal units in petroleum systems analyses are oftentimes challenging and overlooked. The role of seal lithologies are crucial in CCUS where highly fractured horizons lead to leakage and can be detrimental to long term carbon storage.
Solution: Low Permeability Seals
Seal quality directly determines the amount of resources available to be stored long-term in reservoirs. In instances where reservoirs are drained, and sufficient storage is present for carbon sequestrations, low permeability seals that lack fractures are preferred. In order to estimate the seal quality, outcrops if available can be used. In the case of absence of outcrops, FMI (Formation microresistivity imaging) can provide a high-resolution understanding on the amount and orientation of fractures in a formation.
In conclusion, reservoir characterization is a crucial step in the process of carbon storage, but it also poses several challenges that must be addressed. By utilizing advanced data acquisition and interpretation techniques, numerical simulation and modeling, and more, these challenges can be overcome, allowing for the safe and effective implementation of carbon storage.
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