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Characterization of Reservoir Fluids based on Perturbation from n-Alkanes
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Fluid Characterization with the PnA Method
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- Author / Creator
- Kumar, Ashutosh
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Reliable design of gas and/or steam injection for enhanced oil recovery requires compositional reservoir simulation, in which phase behavior of reservoir fluids is represented by an equation of state (EOS). Various methods for reservoir fluid characterization using an EOS have been proposed in the literature. Conventional characterization methods addressed the challenge of the reliable prediction of the condensation/vaporization mechanisms in gas injection processes. It is even more challenging to characterize reservoir fluids for multiphase behavior consisting of three hydrocarbon phases. Complex multiphase behavior was observed experimentally for many gas floods. The importance of considering multiphase behavior in gas flooding simulation was also demonstrated in the literature. However, no systematic method has been proposed, especially for three-phase characterization. The main objective of this research is to develop a reliable method for multiphase fluid characterization using an EOS. The Peng-Robinson EOS is used with the van der Waals mixing rules in this research. The fluid types considered are gas condensate, volatile oil, black oil, heavy oil, and bitumen. The most important difference from the conventional methods is that, in this research, reservoir fluids are characterized by perturbation of the EOS model that has been calibrated for n-alkanes, in the direction of increasing level of aromaticity. This methodology is referred to as perturbation from n-alkanes (PnA), and used consistently throughout the dissertation. The experimental data required for the characterization methods presented in this dissertation are the saturation pressure and liquid densities at a given temperature, in addition to compositional information. Other types of experimental data, such as minimum miscibility pressures, liquid dropout curves, and three-phase envelopes, are used to test the predictive capability of the PR EOS models resulting from the PnA method. First, the PnA method is applied to simpler phase behavior that involves only two phases of vapor and liquid. The Peng-Robinson EOS is calibrated for vapor pressures and liquid densities for n-alkanes from C7 to C100. Two different characterization methods are developed for two-phase characterization using the PnA method. In one of them, fluid characterization is performed by adjusting critical pressure, critical temperature, and acentric factor. In the other, fluids are characterized by directly adjusting the attraction and covolume parameters for each pseudocomponent. Then, the PnA method is extended to three phases. Unlike for two phases, the Peng-Robinson EOS is calibrated for three-phase data measured for n-alkane/n-alkane and CO2/n-alkane binaries. A new set of binary interaction parameters (BIPs) is developed for these binaries, and applied for reservoir fluid characterization. The PnA method applied for two and three phases results in three different methods of fluid characterization. They are individually tested for many different reservoir fluids to demonstrate their reliability. The validation of the methods is based on experimental data for 110 fluids in total (50 gas condensates, 15 volatile oils, 35 black oils, 4 heavy oils, and 6 bitumens). Results consistently show that the use of the PnA method with the PR EOS yields a systematic, monotonic change in phase behavior predictions from n-alkanes. The two characterization methods developed for two phases do not require volume shift to obtain accurate predictions of compositional and volumetric phase behavior. However, they may not give reliable predictions for three phases. The three-phase characterization presented in this research is the most comprehensive method that can predict reliably two and three phases. However, volume shift is required for matching density data in this last method. Therefore, it should be used with a proper understanding of the relationship among different EOS-related parameters and their effects on phase behavior predictions.
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- Graduation date
- Spring 2016
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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.