Kintetics Of Thermal Visbreaking Of A Cold Lake Bitumen

Abstract

HEAVY OIL Kinetics of thermal visbreaking of a Cold Lake bitumen W.R. SHU and V.N. VENKATESAN Mobil R&D Corp. Dallas, Texas, U.S.A. ABSTRACT This paper presents a study on the kinetics of visbreaking under conditions commonly encountered in thermal recovery processes. Batch visbreaking of a Cold Lake bitumen was con-ducted at 260 -325'C with residence times of up to one month. A simple phenomenological model was developedfor the visbreaking kinetics, wherein the oil was first cracked to a less viscous species and the latter then imposed a solvent effect on the former. The Cold Lake data were used to validate the model. A comparison with some literature data on an Atha-basca bitumen was also made. The first order kinetic constant of visbreakingfor Cold Lake bitumen has an activation energy of 31 Kcallg-mote. The kinetic data may be used to assess the importance of visbreaking in a thermal recovery process. It also supplements visbreaking data at more severe conditions requiredfor surface upgrading of heavy crudes and bitumens. Introduction High viscosity is a major constraint in the production and pro-cessing of heavy oils and oil sand bitumens. Thermal recovery processes such as steamflooding or in-situ combustion are effective in temporarily lowering the oil viscosity and enhanc-ing its production. Field evidence, however, indicates that a permanent viscosity reduction, or visbreaking, also accom-panies these processes which can result in partial upgrading of the heavy crude. In-situ visbreaking is characterized by mild decomposition, minimum coke formation, and the retention of products in the liquid phase.In-situ visbreaking of heavy oils has been the subject of several earlier studies. For example, McNab et al.(1) studied the visbreaking of Athabasca bitumen and associated the observed chemical changes to its origin and evolution. Erdman and Dickie(2) made a similar study on asphaltic crudes. Henderson and Weber(3) studied the visbreaking of several heavy oils and obtained time-temperature relationship for the physical up-grading of each oil. Hayashitani et al. (4) reported an extensive study on the thermal cracking of Athabasca bitumen. All of their data except two points, however, were taken in the temperature range of 344 -452'C, beyond the mild condition studied here for in-situ visbreaking.The present work reports the results of our systematic in-vestigation on the visbreaking of a Cold Lake bitumen in the temperature range of 260 -325'C for up to 720 hours. The ob-Keywords: Heavy oil, Visbreaking, Cold Lake, Athabasca bitumen, Kinetics, Thermal recovery, Viscosity. Paper reviewed and accepted for publication by the Editorial _ 60 jective was to provide kinetic data for visbreaking as input to reservoir simulators. A simple phenomenological model for visbreaking was developed to derive kinetic rate constants from the Cold Lake data. The model was also applied to Henderson and Weber data(3) on Athabasca bitumen to fur-ther validate the model. Experimental The Cold Lake bitumen sample was obtained from the...

Mathematical Modeling of Thermal Conversion of Athabasca Bitumen. Part I: Reaction Pathways and Experimental Method

“…Cycloparaffin Bridge CH (1) Cycloparaffin Alkyl-Substituted CH (2) Cycloparaffin CH 2 (3) Methyl-cycloparaffin (4) Ethyl-cycloparaffin (5) to Cycloparaffin ring (6) Paraffin chain (7) Aromatic and Olefinic: (4) Ethyl-aromatic (5) Diphenyl methane CH 2 (6) to Aromatic (7) Olefinic CH and CH 2 (8) to Olefinic (9)…”

“…In models proposed by Shu and Venkatesen (5) and Krishna et al (6) , visbreaking was described with two pseudo-components: a feed and a product. This approach only required one overall reaction, and the reaction predicted how much of the feed was converted into product.…”

“…This approach only required one overall reaction, and the reaction predicted how much of the feed was converted into product. The model proposed by Shu and Venkatesan (5) was based on Cold Lake bitumen while that proposed by Krishna et al (6) used Agjahari long residue as its feedstock. Each feedstock had its own set of pre-exponential factors and activation energies, illustrating that the fit of this type of model was feed-dependant.…”

Mathematical Modeling of Thermal Conversion of Athabasca Bitumen

“…In the models proposed by Shu and Venkatesen (5) and Krishna et al (6) , visbreaking was described with 2 pseudocomponents, a feed and a product. This approach only required one overall reaction, and the reaction predicted how much of the feed was converted into product.…”

“…This approach only required one overall reaction, and the reaction predicted how much of the feed was converted into product. The model proposed by Shu and Venkatesan (5) was based on Cold Lake Bitumen while the model proposed by Krishna et al (6) used Agjahari long residue as its feedstock. Each feedstock had its own set of preexponential factors and activation energies, illustrating that the fit of this type of model was feed-dependant.…”