The widespread implementation of carbon capture, utilization, and storage (CCUS) calls for a rigorous assessment of the associated risks if leakage occurs. Depleted oil reservoirs, due to the economic benefit associated with enhanced oil recovery will be the first adopters of CCUS. Residual hydrocarbons present in these reservoirs may migrate with CO2 and/or brines if leakage occurs. The necessity of understanding the mechanisms that control the solubility of organic compounds in both CO2 and brines is incumbent. Here, we present the trends associated with the solubility of organic compounds in supercritical CO2 (sc-CO2), and how the presence of high concentrations of electrolytes affects the solubility of organic compounds in brines. There are three main trends that are associated with solubility of those compounds in sc-CO2. First, compounds with relatively higher volatility have higher solubility in sc-CO2. Second, the partitioning of organic compounds from water to sc-CO2 is controlled by the relative solubility of the organic compound in each phase. Thirdly, the presence of organic compounds with high volatility will enhance the solubility of organic compounds with low volatility in sc-CO2; this is known as the co-solvency effect. In regards to the solubility of organic compounds in brines, the presence of salts decreases the solubility of organic compounds in water. This is called the salting-out effect, and this phenomenon has been modeled up to seawater conditions by the Setschenow Equation, which predicts a log-linear decrease in aqueous solubility with increasing salt content. In this study, we tested the validity of the Setschenow Equation for several key classes of petroleum hydrocarbons (polycyclic aromatic hydrocarbons, thiophenes, and polar compounds) in NaCl waters. Experiments were conducted using solid phase microextraction and samples were analyzed by gas chromatography coupled with a flame ionization detector. The Setschenow Equation has proven to be valid for several of the compounds analyzed, including thiophene, dibenzothiophene, and naphthalene; however it experienced a plateau at high salt concentrations for benzothiophene, phenanthrene, and fluorene. It is hypothesized that this deviation from the Setschenow Equation is occurring for compounds with larger salting-out effects.

Fate of organic compounds in carbon storage environments

248th National Meeting (2014)

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