• Energy Research

Abstract Unconventional oils are very viscous and immobile at reservoir conditions; hence, recovery techniques that are used in conventional reserves are not applicable and practical for heavy oil and bitumen resources. Thus, addition of heat or solvent is required to reduce viscosity of these fluids for both recovery from reservoir and transportation. Thus, in this study, the viscosity of Athabasca bitumen and n-hexane mixtures was measured at different temperatures, pressures, and solvent weight fractions. The results indicated a huge reduction in viscosity of bitumen by increasing the temperature and/or dissolving the solvent. The viscosity of the mixtures showed a curvilinear trend with respect to the solvent weight fraction and temperature. The impact of pressure on the mixture viscosity is more pronounced at lower solvent weight fractions and lower temperatures. The evaluation of different models for mixture viscosity indicated that the power law and Cragoe׳s models represent the viscosity data over wide range of operating conditions better than other models.

Summary This paper presents the density and viscosity measurements for a condensate sample, Athabasca bitumen, and Athabasca bitumen/condensate mixtures applicable for in-situ bitumen-recovery methods and pipeline transportation. The measurements for the densities and viscosities are reported at different temperatures (ambient to 200°C) and pressures (atmospheric to 10 MPa). For mixtures, a wide range of solvent fractions (5-50 wt%) is investigated. The data for the mixtures are also evaluated with predictive schemes as well as with correlation models representing certain mixing rules proposed in the literature. The results indicate that mixture densities are well represented by the excess-volume method, with an average absolute relative deviation (AARD) of 0.78%. The Bij model predicts the mixture viscosities with an AARD of 11.7%.

Abstract World production of heavy and extra-heavy oils has increased as the production of conventional crudes decline. However, the conventional oil recovery methods cannot effectively recover the heavy oil due to their high viscosities. The steam and/or solvent-based recovery processes can be considered as an efficient method for recovery of these resources. The performance of these techniques depends on the amount of solvent dissolved in the crude and the variation of oil viscosity with temperature. Thus, full understanding of the quantitative effects of the solvent on heavy oil viscosity and phase behaviours are crucial for feasibility studies, design and prediction of field-scale processes. Phase behaviour study of bitumen diluted with heavy hydrocarbon solvents such as propane and butane have gained less attention in recent years. These solvents, as good candidates for recently developed recovery methods such as Expanding Solvent Steam-Assisted Gravity Drainage (ES-SAGD), would provide promising oil production rates. The aim of this research, thus, is the development of an understanding of the phase behaviour of butane / Athabasca bitumen systems. It deals with both vapor-liquid and liquid-liquid phase equilibriums over wide range of temperatures (up to 200°C) approaching the conditions of in situ steam processes and pressures up to 8 MPa. Experimental results indicated that the vapor-liquid and liquid-liquid equilibrium formed over the studied temperature and pressure ranges. In the case of vapor-liquid equilibrium, the dissolved butane in bitumen leads to a significant oil viscosity reduction. The effect was higher at lower temperature and higher pressure. For liquid-liquid equilibrium, butane extracted light components from oil and formed a butane-enriched phase while the heavier constitutes such as asphaltene separated as second heavy liquid phase. Finally, the measured solubility and density data were adequately modeled with Peng-Robinson equation of state.

AbstractSteam assisted gravity drainage (SAGD) has been known as a commercially proven high ultimate recovery process for bitumen and heavy crudes. It is an energy intensive process, which is economical when oil price is above certain value. When the oil price goes below the economic threshold of project, steam injection can be decreased or completely stopped for a certain period of time, and can resume thereafter when the condition alters. The objective of this study is to provide comprehensive information about the effect of steam injection interruptions on thermal project performance. An optimization strategy for the SAGD process, in cases where steam injection interruption occurs, is discussed using actual reservoir models of different geological formations. An economical model is used to evaluate operating strategy effect on the net present value (NPV) of the project. The parameters, like shut‐in period, initial steam injection period, etc, are optimized for Athabasca type oil sand reservoirs. The results show several key mechanisms exist in the life cycle of the SAGD process that must be included to reflect the field scale behaviour; otherwise, the mechanistic simplicity of the models could lead to directional and semi‐quantitative conclusions. Among the mechanisms, temperature effect on basic petrophysical properties of reservoir rocks was found to have an important role in the oil recovery, and considerably impacts the results of optimization. When the steam injection is interrupted, an optimum shut‐in period can be determined to maximize the oil recovery. The optimum length of steam injection interruption depends on the initial steam injection period.

Underground coal gasification (UCG) as an efficient method for the conversion of the world’s coal resources into energy, liquid fuels, and chemicals has attracted lots of attention in recent years. This paper is concerned with a feasibility study of the UCG process for Alberta reservoirs using the three-dimensional simulation of this process based on a unique porous media approach. The proposed approach combines the effects of heat, mass transport, and chemical reactions to achieve this goal. The Computer Modeling Group (CMG) software STARS is used for simulation. The geological structure including coal and layers interspersed between coal seams (claystone layers), the porosity/permeability variation, and the chemical processes with corresponding parameters are considered in the model. Chemical stoichiometry coefficients of the pyrolysis process are calculated from proximate and extended experimental data. Genetic algorithm and pattern search are used for parameter estimation. This model is developed to s...

Abstract One of the main challenges in the phase behavior study of heavy crudes such as bitumen and solvent systems is the long equilibration time. The equilibration time depends on the experimental conditions, such as pressure and temperature, as well as solvent and oil properties. Oil viscosity is the key factor for the equilibrium time especially at low temperature approaching reservoir condition where the oil viscosity (e.g. Athabasca bitumen) is in the order of million centipoises. Thus, a method to speed up the phase behavior experiments for heavy crudes is essential. The proposed experimental apparatus in our previous study [7] was modified. The modification speeds up generating the experimental data with the capability of conducting parallel experiments. Thus, two or three experiments can be conducted at the same time period. Total cost for this apparatus is almost the same as our pervious apparatus while more experimental data can be produced with this new design. In addition to heavy crude/solvent systems, the proposed apparatus has the capability of conducting the experiments for simple binary systems. The new apparatus was tested for the saturation pressure measurement of pure hydrocarbon, the phase behavior study of simple binary systems, and the phase behavior study of Athabasca bitumen/solvent systems (solvents: methane, ethane, and propane) in the case of vapor–liquid and liquid–liquid equilibrium conditions.

AbstractPhase behaviour modelling of reservoir fluid is a fundamental step for reservoir simulation. Furthermore, as the complexity of the recovery process increases, the fluid model plays a more important role in the reliability of the simulation outputs. Although the in situ combustion enhanced oil recovery method (ISC) is one of the most complex recovery techniques available in the petroleum engineering literature, for most of the simulation jobs related to this elaborate process only simple and rudimentary fluid characterization layouts are considered. In this work, the principal fluid properties of Athabasca bitumen with regard to the ISC process are recognized, extracted from the literature, validated for consistency, and used for the development of an inclusive and accurate fluid model. Then the fluid model is fully developed while considering the ISC reaction kinetics so that the model has both accuracy, indispensable for phase behaviour modelling, and consistency, essential for the reactions definitions.

Phase behavior properties of (bitumen + solvent) systems have a significant effect on surface upgrading methods and are necessary for the recovery of bitumen from reservoir. In this study, the phase partitioning and component distribution between phases as well as phase properties at equilibrium condition for the (Athabasca bitumen + ethane) system at room temperature were experimentally evaluated. The experiments were conducted using a designed pressure–volume–temperature (PVT) apparatus to obtain liquid–liquid equilibrium properties as well as extraction yield for (bitumen + solvent) systems. In addition, the equilibrium k-value for each component present in the mixture at equilibrium condition was calculated on the basis of compositional analysis of liquid phases and available correlations for the molecular weight of heavy components. The impact of pressure and solvent to bitumen ratio on the boiling point curves and compositional analysis of flashed off liquids as well as equilibrium k-values were eva...

Abstract World production of heavy and extra heavy oils has increased as the production of conventional crudes declines. However, conventional oil recovery methods cannot effectively recover heavy oils due to their high viscosities. Different techniques for the recovery of these resources, such as enhanced solvent-steam-assisted-gravity-drainage (ES-SAGD), have been patented. The performance of these methods depends on the amount of solvent dissolved in the oil and its phase behavior properties. Solvent-based recovery processes have lower green house gas emissions and can also contribute to in-situ upgrading of oil. The oil upgrading can be achieved either by the deasphalting or partitioning of the oil mixtures into two liquid phases in which higher grades of oil than the original oil produced. Experimental data on the phase behavior is needed to determine the operating conditions that cause the liquid-liquid system or in situ upgrading. In the present study, the in situ upgrading of heavy oil using propane was experimentally determined at different temperatures and pressures. The effect of the solvent-to-oil ratio on equilibrium compositions and saturated phase properties were measured. The distributions of different components in both phases were observed with simulated distillation (SimDis) analysis. The amount and type of components that was extracted by propane has been investigated. The experimental results showed that propane/oil mixtures partitions into a solvent and asphaltene-enriched phases at specific conditions. The SimDis data demonstrated that the oil was upgraded by the separation of the heavier constitutes with the light components extracted by the propane into a solvent-enriched phase. Recovery processes can, therefore, be designed in such a way that the valuable components are extracted from the heavy crude at specific in situ conditions, to produce higher grades of oil than original heavy oil.

Steam–solvent coinjection processes have received more attention in the past decade due to the environmental impact of the pure steam injection process. Increasingly restrictive environmental regulations including carbon tax have served to push the industry to consider coinjection processes (steam + solvent) to reduce greenhouse gas emissions. Understanding the phase behavior of solvent/bitumen mixtures is critical for feasibility studies as well as the design and implementation of a successful coinjection process. This study presents the vapor–liquid equilibria for bitumen/ethane mixtures and their applications for bitumen recovery processes. Experiments were conducted for temperatures up to 190 °C and pressures up to 10 MPa to simulate the conditions of in situ steam processes. The results of our vapor–liquid equilibrium experiments include solubility, viscosity, and density measurements of the saturated liquid phase, k-values, and gas oil ratio. Increasing the temperature from 50 to 150 °C resulted in ...