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Quantifying pore geometries using FE-SEM: examples from the San Andres formation and implications for CO₂ storage
Schneider, Mitchell
Schneider, Mitchell
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2023
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Abstract
The Permian San Andres Formation is a prolific conventional carbonate reservoir in the Central Basin Platform (Texas, USA), but vertical and lateral heterogeneity within and between fields make reservoir characterization and thus recovery of hydrocarbons difficult to predict. Carbon dioxide (CO2) flooding has long been used for enhanced oil recovery (EOR) operations within the San Andres Formation, where injectivity volumes and rates are variable. Some fields unintentionally sequester large volumes of CO2, but the rock characteristics that allow both effective CO2 sequestration and high injectivity (e.g., lateral geological heterogeneity, diagenetic evolution, pore-network dynamics, fluid-rock interactions) are still uncertain. Because of the existing infrastructure and the history of CO2 injection, there is a desire to transition these reservoirs into permanent CO2 sequestration sites, but detailed data on pore network complexity is still sparse.
Using thin-section data from the Goldsmith Field on the Central Basin Platform, we quantify heterogeneity within pore networks to provide a ranking methodology for transitioning these reservoirs into permanent CO2 sequestration sites. Using field-emission scanning electron microscopy (FE-SEM), we document the mineralogy and porosity network at 1.6-micron resolution to quantify pore dimensions, pore-lining minerals, and pore-network heterogeneity between different facies and stratigraphic intervals of the San Andres Formation. Integration of these FE-SEM data with existing core-plug porosimetry and permeability quantifies the CO2 injection capability of pore networks within San Andres intervals, providing a methodology to determine the viability of a particular field to be converted to a site for CO2 sequestration. This newly developed and automated methodology can further help determine reservoir viability basin on linking quantified pore network geometries to historical EOR mass balance data in fields that sequester large volumes of CO2. This microscopic technique can help make economic decisions of depleted carbonate and siliciclastic petroleum reservoirs, not only in the Permian Basin, but globally.
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