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Steam-Solvent Coinjection for Bitumen Recovery under Reservoir Heterogeneity with Consideration of Water Solubility in Oil
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- Author / Creator
- Venkatramani, Arun Venkat
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The main objective of this research is to determine if expanding solvent-steam assisted gravity drainage (ES-SAGD), wherein a small quantity of a condensable solvent is coinjected with steam, can be a better alternative to SAGD in highly heterogeneous formations. Specifically, three previously unanswered questions are addressed. Firstly, the effect of dissolution of water in the oleic phase (xwL) on the relative performance of ES-SAGD to SAGD in a synthetic homogeneous bitumen reservoir is examined. Experimental data show that xwL can be significant at elevated temperatures, and the dilution of bitumen by water can lower the viscosity of the oleic phase. However, xwL is disregarded in conventional reservoir simulation practice. Using phase behavior models that were carefully created on the basis of experimental data, the benefit of solvent coinjection relative to steam-only injection in terms of bitumen production is shown to be overestimated by nearly 10% at 35 bars when xwL is disregarded. This mainly comes from the underestimation of the performance of SAGD. Secondly, an investigation is conducted on the effects of reservoir heterogeneity on the relative performance of ES-SAGD to SAGD in terms of the steam-oil-ratio (SOR) as a function of cumulative bitumen production. xwL is considered in these evaluations to ensure reliable assessment of the benefit of solvent coinjection. Using one hundred stochastically-generated realizations of heterogeneous reservoirs comprising of clean sand and mudstone, ES-SAGD is shown to be less sensitive to reservoir heterogeneity than SAGD, and the reduction in SOR due to coinjection for a given cumulative bitumen production is demonstrated to be higher under heterogeneity. This is due to the combination of enhanced mixing between solvent and bitumen under heterogeneity, and the interplay between solvent-bitumen mixing and temperature distribution within the reservoir. Lastly, conditions for flow in heterogeneous reservoirs conducive to significant reduction in the cumulative SOR due to coinjection of solvent are identified in conjunction with an analytical theory for SAGD. Results show that (i) the SOR reduction by steam-solvent coinjection is positively correlated with the increase in SAGD’s SOR due to heterogeneity, (ii) a larger amount of bitumen tends to be diluted in those reservoirs for which SAGD exhibits slow production of bitumen, and (iii) the dilution of bitumen by solvent under steam-solvent coinjection becomes more pronounced where flow barriers restrict the local flow of bitumen in SAGD at elevated temperatures. Accumulation of solvent in such heated slow-flow regions can facilitate a substantial increase in the flow rate of bitumen through the simultaneous reduction of the oleic-phase viscosity and improvement of the oleic-phase relative permeability by enhancement of the oleic-phase saturation. The interplay between dilution of bitumen by solvent and temperature can further facilitate the reduction of the cumulative SOR by mitigating thermal losses.
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- Graduation date
- Fall 2017
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- Type of Item
- Thesis
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- Degree
- Doctor of Philosophy
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- License
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.