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Investigating Light Solvent Aided Process in Cold Lake Oil-Sand Reservoir Using Experimental and Numerical Approaches

  • Author / Creator
    Eghbali, Sara

  • Steam assisted- gravity drainage (SAGD) is the main in-situ bitumen recovery process in which saturated steam is injected into the bitumen zone. However, it has some drawbacks, which include high-energy consumption and significant environmental concerns. Solvent Aided Process (SAP) is a method proposed to improve SAGD’s efficiency and to reduce its associated emissions by reducing Cumulative Steam Oil Ratio (CSOR). Previous studies showed that co-injecting steam with a wide range of solvents including normal alkanes from C4 to C8 and diluents improved oil production rates and reduced CSORs. Although co-injecting solvents with steam has improved bitumen recovery, understanding the effect of key parameters controlling SAP’s performance and designing an optimum co-injection remain challenging. Also, the effects of solvents lighter than C5 such as CO2, C3 and C4 on the efficiency of SAP are not well understood. Understanding and modelling fluid-fluid interactions in solvent-bitumen systems including the phase behavior and viscosity of solvent-bitumen systems is essential for developing an optimum SAP for bitumen recovery. In this research, experimental and numerical simulation studies are undertaken to optimize SAP’s performance by co-injecting steam with CO2, C3 and C4 solvents. The experimental study investigates the phase behavior of CO2-, C3- and C4-bitumen systems. An Equation of State (EOS) is calibrated against the measured Pressure-Volume-Temperature (PVT) data to predict phase behaviour of the solvent-bitumen systems. A robust algorithm is developed for reliable prediction of multi-phase equilibrium. Also, viscosities of these systems are measured and used to modify a viscosity model. The developed algorithm and the calibrated EOS are used to predict phase-equilibrium regions in the compositional space for the solvent-bitumen at elevated temperatures. The calibrated EOS and viscosity model are applied in a simulation model to understand the phase behavior of steam-solvent-bitumen at steam-bitumen interface and to optimize SAP in Clearwater Formation. The simulation study optimizes SAP in terms of solvent type, solvent concentration and co-injection strategy.The advantage of the developed algorithm for multiphase equilibria calculations is robust and efficient prediction of complex phase behavior. This complex phase behavior is possible during SAP where a vapor phase and three liquid phases can coexist (i.e., L1: rich in bitumen component, L2: rich in solvent and W: aqueous phase). Multiphase equilibria and viscosity calculations show that existence of additional solvent above a defined threshold of solvent concentration has limited effect on reducing bitumen viscosity. C4 leads to higher viscosity reduction compared to C3 and CO2. In contrast with CO2 and C3, C4 has the potential of extracting hydrocarbon components in a solvent-rich liquid phase (i.e., L2 phase). Numerical simulations of solvent-steam co-injection show that bitumen rate increases as a result of bitumen dilution. However, bitumen rate decreases after a while to a stabilized value. This happens as condensed water accumulates below the chamber over time. Therefore, condensed solvent accumulates at the top of the accumulated water within a limited region due to the gravity segregation. This causes reduction of the effective contact area between the condensed solvent and bitumen. Consequently, oil production rate stabilizes as more steam-solvent are co-injected. Therefore, an optimum co-injection scenario should be designed to maximize bitumen recovery and efficiency of this process. Bitumen viscosity near the chamber edge is higher for C3-steam co-injection respect to C4-steam co-injection. This is because C3 has less solubility than C4 in the oil phase and chamber temperature is lower in C3-steam co-injection. This leads to more efficicent oil displacement near the edge in C4-steam co-injection compared to C3-steam co-injection. In constrast with C3-steam co-injection, scenarios of C4-steam co-injection with variable solvent concentration and descending trend of solvent concnetration has less ultimate recovery and Net Present Value compared with the constant concentration strategy with optimum concentration. Results show that C3- and C4-steam co-injections lead to increase in bitumen recovery factor and reduction in CSOR over corresponding SAGD scenarios. On the other hand, CO2-steam co-injection causes about 10% reduction in bitumen recovery factor compared to SAGD. Wettability of the reservoir rock has significant effect on performance of SAP using light solvents. Increasing oil wetness of the reservoir increases bitumen recovery. This is because there is less water blockage and more effective contact area between the condensed solvent and the heated bitumen in a more oil wet reservoir.

  • Subjects / Keywords
  • Graduation date
    Spring 2019
  • Type of Item
    Thesis
  • Degree
    Doctor of Philosophy
  • DOI
    https://doi.org/10.7939/r3-ekwy-fm36
  • License
    Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.