Cyclic Solvent Injection Process for Heavy Oil Recovery
Figure 1: Cyclic Solvent Injection Phase Schematic and Pressure Profile Oil
Solvent dissolved in oil Pressure
laboratory-scale experiments under controlled conditions and that can be applied to field-scale simulations. The CSI models described have been developed at AITF over a number of years and continue to be refined as additional field- and laboratory-scale data become available. Numerical simulation is particularly important for developing novel processes, such as CSI, and is used as an aid in selecting field injection-production strategies (injection rate, composition and bottom-hole pressure [BHP]) and in interpreting the results (production rates and compositions) obtained from these strategies.
Primary Production Model
Figure 2: Cyclic Solvent Production Phase Schematic and Pressure Profile
Oil
Prior to simulating CSI in a post-CHOPS reservoir, it is first necessary to simulate the development of wormholes during CHOPS and match BHP, oil, water and gas production, when they are available. Reservoir conditions (effective permeability, fluid saturations and pressure distributions) at the end of primary production are predicted using numerical simulation. Some models representing CHOPS have been described.2–15 and foamy oil models.16
AITF has developed sand transport Cyclic Solvent Injection Model Bubble Solvent dissolved in oil Pressure
Equilibrium Pressure Volume Temperature Behaviour In the Computer Modelling Group STARS simulator, the equilibrium oil
phase mole fraction is represented by the use of Ki values (gas–liquid equilibrium factor) for each component i: Ki = yi/xi
Figure 3: Sample Phase Envelope and Operating Range
2,000 4,000 6,000 8,000 10,000
0
where xi = equilibrium mole fraction of i in oil phase and yi = equilibrium mole fraction of i in gas phase. Ki is a function of temperature and pressure. This relationship should be based on
values measured in the temperature and pressure range of interest. In reality, solvents do not immediately reach their equilibrium concentrations in oil.
Operating range
CSI models have been developed at AITF for CSI based on non-equilibrium gas dissolution and gas exsolution behaviour.17 In these models, the rate at which a gaseous component dissolves or exsolves from oil depends on the difference between its current
012345 Temperature (C)
Bubble point 6789 10 Dew point line
the Saskatchewan Research Council. JIVE included data from three solvent injection field pilots operated by Husky, Nexen and CNRL. Results from Husky’s CSI pilot were encouraging and a mixture of methane plus propane was injected. In Nexen’s CSI pilot, methane-butane solvent was injected; however, in this pilot asphaltene deposition was a concern.1
Numerical Simulation
Numerical simulation and laboratory experiments are important in designing a CSI strategy for a particular reservoir and in interpreting the results obtained during the process. Therefore, it is important to develop simulation models that have initially been verified using
36
The concept of cyclic solvent injection (CSI) was borne
from the need to develop a non-thermal process for thin reservoirs with wormholes.
concentration in the oil phase (xi) and its equilibrium oil phase concentration (xieqm). If non-equilibrium behaviour is ignored, then simulations predict too much dissolution of the solvent near
the wellbore and too little penetration of the solvent into the reservoir. During production, an assumption of instant equilibrium solubility results in an exsolution of gas from oil that is too rapid.
EXPLORATION & PRODUCTION – VOLUME 9 ISSUE 2
Pressure (kPa)
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