An Experimental Study of Multiphase Behavior for n-Butane/Bitumen/Water Mixtures

Abstract

Steam-solvent coinjection has been studied and pilot-tested as a potential method to improve steam-assisted gravity drainage (SAGD) for bitumen recovery. Reliable design of coinjection requires reliable PVT data for bitumen/solvent/water mixtures, which are scarce and fragmentary in the literature. The main objective of this research was to present a new set of PVT and multiphase data for n-butane/Athabasca-bitumen/water mixtures at pressures up to 10 MPa and temperatures up to 160°C. Experiments were conducted by use of a conventional PVT apparatus. The data presented include multiphase equilibria up to four coexisting phases and liquid densities for 100% bitumen, two mixtures of n-butane/bitumen, and one mixture of n-butane/bitumen/water. A single equation-of-state model was developed to correlate all experimental data obtained, and used to interpret complex multiphase behavior observed for the highly size-asymmetric polar mixtures. Liquid-liquid separation of hydrocarbons was experimentally observed at the n-butane concentration of 97 mol% in the n-butane/bitumen system with/without water, for a wide range of temperatures at operating pressures for expanding-solvent-SAGD (ES-SAGD). This may indicate the limited solubility of n-butane in bitumen even when a high level of accumulation of n-butane takes place near a chamber edge in ES-SAGD for Athabasca bitumen. The multiphase transition that involves appearance/disappearance of the vapor phase was observed to occur near the vapor pressure of n-butane or its extension. Such phase transition occurs at a higher pressure in the presence of water, due to its vapor pressure, than in the absence of water at a given temperature. This is the first time four coexisting phases are reported for n-butane/Athabasca-bitumen/water mixtures at temperature-pressure conditions relevant to ES-SAGD.

Modeling of asphaltene and water associations in petroleum reservoir fluids using cubic‐plus‐association EOS

“…Gao et al measured multiphase behavior of n ‐butane/bitumen/water mixtures, and observed the complex phase transitions from WL 2 to WL 1 L 2 to WL 1 L 2 V with decreasing pressure at temperatures 353–433 K. They showed that the PR EOS was not able to accurately represent the WL 2 /WL 1 L 2 boundary for 37.02 mol % n ‐butane + 0.96 mol % bitumen + 62.02 mol % water (“Mixture C” in Gao et al) below 393 K. They observed emulsion for this mixture. In this subsection, the CPA EOS is applied to match the experimental phase boundaries.…”

“…The bitumen density and vapor pressure data given in Gao et al are used to characterize four pseudo components PC1, PC2, PC3, and asphaltene. Table summarizes the parameters for the CPA EOS model.…”

“…This is because the saturation vapor pressure depends mainly on the lighter components in the mixture (i.e., water and n ‐butane), which are not significantly affected by the association properties. Indeed, the PR EOS was shown to successfully represent this phase boundary in Gao et al…”

“… Pseudo components, PC1, PC2, PC3, and asphaltene, were characterized on the basis of the data given in Gao et al BIPs are calculated by use of Eq. .…”

“…Modeling of them is important when they affect oil‐recovery mechanisms and processes; for example, asphaltene precipitation/deposition during CO 2 injection and coinjection of steam and solvent for heavy‐oil/bitumen recovery . In many practical applications, a simple cubic EOS does not offer sufficient flexibility for capturing phase behavior that is more complex than vapor‐liquid‐liquid equilibrium; for example, asphaltene precipitation, water‐asphaltene emulsion, and water dissolution. Modeling such complexities in addition to the hydrocarbon vapor‐liquid‐liquid equilibrium requires including additional mechanistic parameters that account for hydrogen bonding in an EOS.…”