T. Frauenfeld

Investigation of the VAPEX Process Using CT Scanning and Numerical Simulation

The VAPEX process, a solvent analogue of Steam Assisted Gravity Drainage, has attracted considerable attention as a recovery method for heavy oil. However, to date, there are still many questions about the nature and magnitude of basic process mechanisms, and whether the process can produce economic oil rates. The experiments discussed in this paper were aimed at quantifying some of the basic mechanisms, in particular the dispersive mixing mechanism. We have performed a series of topdown solvent injection experiments under varying conditions. utilizing a CT scanner to monitor fluid movements. All of the displacements we have observed are gravity-unstable in the early stages, and characterized by viscous fingering of the solvent into the 5,500 cPoil. After solvent breakthrough, the displacements become stable, dominate by a single solvent finger which has many of the features of a VAPEX solvent chamber. The mixing parameter we infer for these experiments using the Butlor/Mokrys analytic model is higher than that reported for Hele-Shaw VAPEX experiments. An analysis of localized fluid velocities in the experiments using numerical simulation show that the enhanced mixing parameter can be understood as a consequence of convective dispersion in the porous medium. By adjusting the amount of physical dispersion, the simulations can match breakthrough time, post-breakthrough oil rates, and the general character of the fingering. A novel type of quasi-pore scale simulation grid appears to provide advantages in simulating the ustable period at the beginning of the displacements.

Experimental and Economic Analysis of the Thermal Solvent and Hybrid Solvent Processes

Several partially scaled laboratory model experiments were conducted to evaluate a hybrid solvent-steam process for recovery of heavy oil or bitumen. All experiments used Athabasca UTF bitumen, and modelled a 30-metre-thick formation. The experiments were compared using a common set of economic assumptions. The experiments showed that a hybrid solvent-steam process could recover bitumen at steam-oil ratios much lower than those observed for steam assisted gravity drainage (SAGD), and achieve reasonable ultimate oil recovery (60% IOIP). The economic analysis based on experiments indicated that a hybrid solvent-steam process could be more cost-effective than SAGD for a 30-m Athabasca formation.

Experimental Studies of Thermal Solvent Oil Recovery Process for Live Heavy Oil

VAPEX and related processes for the recovery of heavy oil and bitumen have potential application to oils containing some methane in solution. A set of experiments has been completed to evaluate the potential for thermal VAPEX operations in heavy oils containing significant dissolved methane content. Three experiments were run to evaluate a VAPEX process operating in a reservoir in which the oil had significant initial methane saturation. The first experiment tested a 3-component mixture (C 1 -C 2 -C 3 ) that was used in an earlier non-thermal dead oil VAPEX test. The second experiment used horizontally offset wells and 100% ethane as the working solvent. The production well was heated to reflux the solvent in situ. The third experiment also used horizontally offset wells and 100% ethane, plus steam. The steam was injected into the production well to reflux the solvent. Results indicated that the live oil inhibited solvent absorption, and hence production rates, but that a properly designed solvent system could produce oil at reasonable rates. Oil production from the steam-heated well/ethane experiment was similar to that from the electrically heated well/ethane reflux experiment. The experiments provided a database which can be used for economic comparison of process options, and for developing numerical simulations for field predictions.

Viscous fingering effects in solvent displacement of heavy oil

A number of solvent-based processes for the recovery of heavy oil have been proposed in recent years. One of the phenomena that characterizes all such processes, to varying degrees, is viscous fingering. This paper describes the results of a combined experimental/simulation study aimed at characterizing viscous fingering under conditions typical of heavy oil recovery (very high ratios of oil to solvent viscosity). The study also sheds light on other phenomena that are part of such processes. We describe a set of four experiments carried out in heavy oil-saturated sand packs contained within a 30 cm x 60 cm x 1.4 cm visual cell. Three of the experiments involved injection of a miscible, liquid solvent at the bottom of the sand pack, with subsequent upward displacement of the heavy oil; the fourth involved top-down injection of a gaseous solvent. The miscible liquid displacements were dominated by a single solvent finger, which broke through quickly to a producing well at the other end of the sand pack. Observed breakthrough times were consistent with a correlation that describes reported results at lower viscosity contrast. The gaseous solvent experiment exhibited fingering but also had features of a gravity-driven VAPEX process in its later stages. Numerical simulations using a commercial reservoir simulator have been successful in reproducing key features of the experiments. Realistic fingering patterns are produced in the simulations by assuming small, random spatial variations of permeability. The correct modelling of dispersion is crucial in matching the observed phenomena. For gaseous fingering and VAPEX processes, capillary effects are significant and should be included in simulations.

Partitioning of Bitumen-Solvent Systems Into Multiple Liquid Phases

Both gravity-based and cyclic processes for heavy oil/bitumen recovery may involve the use of hydrocarbon (n-alkane) solvent at relatively high solvent/oil ratios. Previous work at ARC has shown that at high solvent loadings, the oil/solvent mixture partitions into a solvent-rich oil phase and a heavy-ends-rich (mostly asphaltene) oil phase. The liquid phases have significantly different densities and viscosities. The partitioning phenomenon could have a significant impact on the performance of gravity-based processes such as Vapex involving solvents, where the low-viscosity liquid phase carries the bulk of the oil production, and the heavier liquid phase consisting of mostly asphaltene is essentially immobile. The solvent-rich phase will consist of the upgraded (de-asphalted) oil. Production of upgraded oil thus would not only enhance the production rate, but also have both economic and pipelining advantages. Data on the physical properties (viscosity and density) and the composition of both the partitioned phases are needed to design and optimize solvent-based processes in reservoir engineering calculations. Phase partitioning experiments conducted at the Alberta Research Council Laboratories along with the experimental data are presented in this paper.

Partitioning of Bitumen-Solvent Systems into Multiple Liquid Phases

Both gravity-based and cyclic processes for heavy oil/bitumen recovery may involve the use of hydrocarbon (n-alkane) solvent at relatively high solvent/oil ratios. Previous work at ARC has shown that at high solvent loadings, the oil/solvent mixture partitions into a solvent-rich oil phase and a heavy-ends-rich (mostly asphaltene) oil phase. The liquid phases have significantly different densities and viscosities. The partitioning phenomenon could have a significant impact on the performance of gravity-based processes such as Vapex involving solvents, where the low-viscosity liquid phase carries the bulk of the oil production, and the heavier liquid phase consisting of mostly asphaltene is essentially immobile. The solvent-rich phase will consist of the upgraded (de-asphalted) oil. Production of upgraded oil thus would not only enhance the production rate, but also have both economic and pipelining advantages. Data on the physical properties (viscosity and density) and the composition of both the partitioned phases are needed to design and optimize solvent-based processes in reservoir engineering calculations. Phase partitioning experiments conducted at the Alberta Research Council Laboratories along with the experimental data are presented in this paper.