Low temperature oxidation (L TO) has long been recognized as one of the dominant mechanisms controlling fuel availability in in-situ combustion. Its effect on the physical properties of crude oils is also well known. In spite of these fmdings, the prevailing conceptual model of in-situ combustion still hinges on thermal cracking (in isolation) ahead of the firefront, to provide sufficient fuel (coke) for propagation of the reaction zone. Previous simulation studies, which purported to include L TO as part of the reaction scheme, have unrealistically specified the reaction products as carbon oxides and water. Furthermore, oil compositional changes due to oxidation have been completely neglected.This paper describes a unified pseudo-mechanistic reaction model for mathematical modeling of in-situ combustion of Athabasca bitumen. The model represents a consolidation of individual experimental kinetic studies on thermal cracking and low temperature oxidation of Athabasca bitumen, and reported data for the high temperature oxidation of coke. The formulation is comprehensive in that it allows bitumen to undergo density and viscosity increases, as well as reduced reactivity to oxidation, with increased oxidation extent. Hydrocarbon bypassing due to quenching of the combustion front is also permitted with the proposed kinetic model.The paper includes application of the reaction model in numerical simulations of adiabatic combustion tube tests performed on Athabasca bitumen. A significant feature of the model is its ability to predict the dual oxidation uptake peaks associated with ramped temperature oxidation experiments.

FIGURE 2 Aqueous phase trapping in an oil or gas reservoirrelative permeability relations. FIGURE 3: Illustration of variation of Sw irr with permeability and capillary geometry.FIGURE 4: Illustration of effect of relative permeability curve configuration on severity of aqueous or hydrocarbon phase trapping. The Journal of Canadian Petroleum TechnologyFIGURE 6: Illustration of apt correlation for preliminary diagnosis of aqueous phase trap problems.

Solids precipitation from reservoir crudes has been recognized as a serious detriment in numerous oil systems world wide. Precipitation may result in in situ permeability reductions as well as contributing to serious plugging problems in surface facilities. The latter can be treated with periodic cleaning techniques (xylene or toluene injection and/or mechanical treatment) but, rather than concentrate on remedies, prevention would be a preferable approach. This paper describes experimentally determined solids precipitation trends as a function of hydrocarbon solvents added. Techniques for the measurement of solids precipitation at reservoir conditions are reviewed and the implementation of a high-pressure high temperatureLASER cell is described. Three solids precipitation models were developed as companions to the experimental program. The models co1l.Sisted of an EOS methodology to calculate vapour-liquid equilibria but then three different models were evaluated for the liquid-solid interaction. The first was a pure component solid phase fugacity correlation, the second a regular-solution-theory multi component model found in the literature and the third was the same multi component solid model but was modified for pressure and temperature influences based on theoretical constructs. A comparison of the three models is included with quantitative comparisons between some experimental data sets and Theory. Future direction of this project is also discussed. Introduction Solids precipitation from reservoir fluids has been a problem for many years. Katz and Beau(1) were some of the first to begin researching the problem and many worthy groups have continued to study the phenomenon. The range of research efforts has been broad but there has been basically two approaches: the first has been associated with clean-up methods such as improved means of unplugging Lines or solids dissolution, whereas the second has been interested in mitigating solids precipitation before it happens, One approach is remedial and the other preventative and many centres are now applying a combination of the two. The significance of the solids precipitation has been established by many and Leontaritis and Mansoori(2) have reported the technical and economic impact with respect to numerous oils throughout the world. The unanimous conclusions of all who have researched the phenomenon indicate that the economic impact, due to reduced productivity, is substantial and requires efficient resolution but that the problem is very complex and has to date resisted an adequate description. Experimentation has yielded a number of general trends but their quantification appears to be intractable as yet. Complex molecular-scale theories incorporating resin-asphaltene interaction and electrokinetic phenomena are beyond present analysis. There are, however applied methods which can be used in semi-quantitative analysis of the solids precipitation problem. Over the last five years Hycal Energy Research Laboratories Ltd. has performed experimental and theoretical research into solids precipitation and considerable insight into the phenomena has been acquired. This paper describes the experimentation done to determine important trends and provides an overview of three theoretical equation-of-state models developed. Previous Work Initial research into solids precipitation concentrated on structure and characterization of the compounds.

More than ninety low-temperature oxidation tests were performed on Athabasca bitumen in the presence of rock matrix and water. These tests were run to evaluate the role of low-temperature oxidation with regard to oil composition and to develop kinetics parameters for application in numerical combustion simulators. This program was initiated as experience with laboratory combustion tube tests indicates that both low-temperature oxidation and thermal cracking reaction kinetics are required to predict the oxygen requirements and oil production performance. In addition to the Whole bitumen runs, tests were also conducted using maltenes, asphaltenes and the heavy oil fraction of the bitumen as the starting material. All work was performed in plug flow reactors at a total pressure of 4190 kPa (600 psig). Feed gas oxygen concentrations were 5, 10 and 50 mole per cent. The temperature varied from 22 °C to 275 °C and the time, from 4 to 72 hours. The gas phase was analyzed during the tests to follow the oxygen uptake history. After unpacking, the residual and produced hydrocarbons were analyzed in terms of mass per cent coke, asphaltenes and maltenes. It was found that the oxygen uptake rate did not follow typical Arrhensus behaviour over the temperature range investigated. The effect of the oxygen partial pressure was very important at low temperature but the reaction order, with respect to oxygen partial pressure, approached zero at temperatures in the range of 175 °C. Three definable low-temperature oxidation reaction regimes were identified. Transitions between the regions were characterized by the rapid formation of coke and the virtual disappearance of the asphaltenes fraction. Times corresponding to the transitions were found to depend on both temperature and oxygen partial pressure. Modelling of the region prior to coke formation was found to be described by a slightly modified version of the previously developed model of Adegbesan (1982). Simple relationships have been developed to describe the experimental coke, asphaltenes and maltenes (by difference) yields as a function of time, for the other two regions. Introduction Oxygen consumption and oil production are the important considerations in the design and operation of an in-situ process. Under high temperature (above 300 °C and ideal sweep conditions such as those normally associated with dry laboratory combustion tube tests, both the oxygen requirements and oil production are closely related to the fuel availability. Fuel for high-temperature combustion is that portion of the original oil which is consumed to form carbon oxides and water. Oil production is dictated by fuel consumption since no appreciable hydrocarbon remains behind the burning zone and all oil other than that burned is recovered. Oxygen requirements are related to the fuel availability through the oxygen / fuel ratio which is generally in the order of 2.3 m3(ST)/kg, hence a knowledge of the fuel requirements for a given reservoir allows for estimation of the operating and economic parameters. It is for this reason that traditional in-situ combustion literature concentrates on fuel availability [Showalter (1962) and Alexander et al. (1957)].

Relating have been determined between wettability and the two-phase relative permeability saturation properties of three consolidation intergranular cores. Wettability was defined by the contact angel (θ), measured external to the porous medium, and by the ability of a fluid to spontancously imbibe into the porous system. Close control over the wettability was achieved in these tests by using synthetic cores composed of polytetrafluoroethylene (PTPE) and various pure fluid paris which displayed essencially uniform wetting behaviour with the solid. The PTPE media, which were of widely differing porousity and permeability, provided systems of fixed pore geometry which were ideal for systematic studies of the wettability variable. Certain comparisons with published work suggested that the PTPE cores were representative models of naturally occurring intergranular porous media. Results determined during the study suggested that wettability effects may predominate over influences from the detailed pore structure. Relative permeability test results indicated that the most efficient immiscible displacement was obtained with fluids capable of spontaneously imbibing into the porous media. Relative permeability saturation relations were media. Relative permeability saturation relations were virtually independent of (θ) for displacements with imbibing fluids. As (θ) was increased through values for which imbibitions did not occur, a consistent shift in the relative permeability properties of both phases was found when the media contained an initial irreducible saturation of the displacing phase. For drainags or forced displacements from a core initially saturated with one fluid, relative permeability curves were little affected when the system contact angel through the displacing phase was varied over the range of 180 to 90 degrees. The sensitivity of the relative permeability relations to contact-angel changes was strongly influenced by the saturation history of a core. Introduction and Background EFFECT OF WETIABILITY ON DISPLACEMENT THE EFFECT of wettability on immiscible displacement has been studied by many investigators over the past few decades(1). It is well recognized that the relative wetting preference displayed by oil and water for the reservoir rock has a strong influence on the behaviour of a waterflood or natural water drive. Wettability has, in fact, been described as the single most important variable affecting the recovery history of a Waferflood(2,3). Reservoir performance calculations and estimates of residual oil saturation are often based on laboratory flow tests with representative core samples believed to possess the wetting characteristics of the reservoir. An accurate assessment of the residual oil saturation is also very important for the evaluation of tertiary recovery processes(4). The influence that wettability has on the microscopic distribution and configuration of residual oil within the pore spaces of the rock could be important in the design and application of surfactant or micro-emulsion floods. Despite the large past effort that has been devoted to studies of wettability effects in porous media, the large number of recent reports on this subject indicate that many aspects are still not well understood. Rathmell et al.(4) have recently summarized some of the areas of conflict.