Estimating CO₂ plume size: A correlation for site screening

Plume size is an important factor in the consideration of a site for CO₂ sequestration. Flow model simulations are the accepted means of estimating plume size, but the development of geologic and numerical flow models requires a significant quantity of data, analyses and staff resources. These may not be readily available. Additionally, a proper geologic model should reflect all of the available rock and fluid properties and a general understanding of the dominant mechanisms influencing CO₂ injection and movement in the injection interval. The time and resources required for flow model simulations can be substantial.During site screening, when multiple sites are being considered, rigorous modeling of the geology of a site may be impractical and cost prohibitive. In such a situation, a reliable correlation tool that would provide a comparative indication of plume size at different sites and provide a hierarchy of site choices for additional tests and analyses or for advanced geologic modeling would be desirable.A right circular cylinder was used with a range of Monte Carlo-derived storage efficiency factors to estimate CO₂ plume size (lateral extent). The cylinder was described using net thickness and effective porosity. The storage efficiency factor included four displacement efficiency terms, which were areal, vertical, gravity, and microscopic displacement efficiency. For site screening, it was assumed that there was more certainty in thickness and porosity at a specific site than for basin-scale (regional) screening. Consequently, the correlations in this paper require the cumulative mass of injected CO₂, net thickness, and effective porosity.The plume size correlations were compared with 13 flow model simulations where net thickness, cumulative CO₂ injection, and permeability were varied. Plume size values obtained from the 13 models compared very well with the plume size values obtained from the right circular cylinder correlations. Additionally, the storage efficiency values from each model compared well with the storage efficiency values obtained using the Monte Carlo simulations. The method was applied to published data on the Sleipner CO₂ storage field and gave relatively good results considering the elliptical shape of the Sleipner CO₂ plume.