Cyclic Solvent Injection Process for Heavy Oil Recovery Figure 8: Gas Saturation
0.35 0.31 0.28 0.25 0.21 0.17 0.14 0.11 0.07 0.04 0.00
Figure 9: Propane Mole Fraction in Oil
0.50 0.45 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00
Figure 10: Carbon Dioxide Mole Fraction in Oil
Cyclic Solvent Injection Model Validation Experimental results were used to validate the simulation approach for CSI. For example, one experiment consisted of primary production followed by six solvent (28 % propane, 72 % carbon dioxide) injection cycles.
0.70 0.63 0.56 0.49 0.42 0.35 0.28 0.21 0.14 0.07 0.00
on laboratory measurements for the particular solvent and oil being used. Mechanical dispersion in porous media results from complex flow paths and is caused by velocity gradients, heterogeneous flow paths and mechanical mixing that is independent of molecular diffusion. Both longitudinal (in the flow direction) and lateral
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.
(perpendicular to flow) mixing are controlled by convection at high velocities and by diffusion at low velocities.18,19
dispersion is greater than transverse dispersion. In a problem, dispersion coefficients should be based on characteristic length
38 Longitudinal
The physical model captures the radial flow of fluids into and out of a 6 cm diameter wormhole during primary cold production and follow-up processes (see Figure 5). The stepped cone laboratory model (3 m long) was constructed from sections of pipe that approximated the cross-sectional flow area of the irregular cone (see Figure 5). The inside diameter of the bottom cylinder of the stepped cone was 1 cm and that of the top cylinder was 12 cm. The model was packed with cleaned reservoir sand and then flooded with water followed by live Lloydminster oil with a gas oil ratio of 8 STD m3/m3 of oil. During the experiment, the model was configured in a vertical alignment with the narrow end down. Information on the experiment is provided in Table 1.
Oil recovery after primary production and six solvent cycles was 50 % (see Figure 6), which indicates the potential viability of the CSI process. Primary production was history-matched using an AITF foamy oil model and a 300 x 1 x 1 radial grid. The primary production simulation resulted in a predicted characterisation (fluid saturations and pressures) of the oil sand pack at the start of CSI. The history match of the CSI cycles was used to validate the CSI model. The oil production match (see Figure 7) indicated that:
• the important mechanisms are represented in the models; and • significant oil swelling by solvent dissolution occurs during solvent injection and can reduce solvent injectivity and penetration into a heavy oil reservoir.
At the end of the first solvent injection period, negligible gas saturation was obtained at the top of the test bed (model height 140–300 cm) in the simulation (see Figure 8). This resulted from oil swelling due to solvent dissolution, which essentially eliminated the gas saturation and impeded solvent penetration. This implies that for an application of the CSI process, the primary production period should be extended long enough to create low oil saturation near the well and increase subsequent solvent injectivity. The propane concentration in the oil phase was much lower at the top of the model than at the bottom (see Figure 9). As a result of its greater concentration in the injected gas and its lower solubility, carbon dioxide reached the top of the oil sand pack and dissolved
EXPLORATION & PRODUCTION – VOLUME 9 ISSUE 2
because they can range from <1 mm to >1 km and from <10 cm to >100 km.20
Diffusion, dispersion, pressure, volume, temperature and non-equilibrium behaviour are all inter-related. This increases the complexity and skill required to model the CSI process for field-scale applications.
Relative Permeability Hysteresis
Bubbles created during gas exsolution dramatically alter relative permeability values during production periods and this effect must be represented in CSI models if foam formation occurs. Foams formed during production are unlikely to be stable if low viscosities are obtained as a result of solvent dissolution.
Start of injection period 1
Start of injection period 1
Start of injection period 1
End of injection period 1
End of injection period 1
End of injection period 1
End of production period 1
End of production period 1
End of production period 1
End of production period 6
End of production period 6
End of production period 6
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