Abstract
During in-situ combustion (ISC) processes, different chemical reactions
occur depending on the temperature level. In heavy oils and bitumens, low
temperature oxidation (LTO) reactions dominate below 300ºC, increasing the
density and viscosity and producing coke which could prevent the success of
ISC. Above 350ºC, combustion reactions dominate, known as high temperature
oxidation (HTO), producing carbon oxides and water. Numerical models tend to
include only thermal cracking and HTO reactions, as LTO reactions are not well
understood. In the present work, ISC experiments operated under LTO were
simulated, using Saturates, Aromatics, Resins and Asphaltenes (SARA) fractions
to characterize the Athabasca bitumen. Concentration profiles and coke
deposition for individual temperatures were matched for isothermal experiments
from 60ºC to 150ºC. Based on these results, ramped temperature oxidation (RTO)
experiments were then modelled, incorporating the heat of reaction at LTO.
Different reaction models were studied to match temperature profiles along the
reactor, oxygen consumption, coke formation and fluids production. This
research will greatly increase the understanding of LTO reactions occurring in
Athabasca bitumen during ISC and contribute to the creation of a reliable
numerical model that predicts ISC performance under ideal (HTO) and,
importantly, non-ideal (LTO) temperature conditions.
Introduction
ISC is a promising but complex oil recovery process in which thermal energy
is generated inside the reservoir owing to combustion reactions between the
heaviest fractions of the oil and an injected oxygen containing gas. For heavy
oils and bitumens, ignition temperatures above 350°C are required to promote
the combustion reactions (HTO). At lower temperatures, other types of reactions
predominate, involving the addition of oxygen to the bitumen, producing heavier
oxidized compounds. The LTO reactions are detrimental to oil production; hence,
ISC processes are designed to operate under the high temperature combustion
regime (HTO). However, LTO reactions occur if the air flux becomes too low to
sustain the combustion reactions, leading to lower-than-estimated production
yields. It has been proven in laboratory experiments that oil recovery is
considerably reduced when LTO reactions occur to some extent, compromising the
success of the ISC.
© 2010. Society of Petroleum Engineers
View full textPDF
(
1,506 KB
)
History
- Original manuscript received:
29 March 2007
- Meeting paper published:
12 June 2007
- Revised manuscript received:
16 November 2009
- Manuscript approved:
11 December 2009
View Cart
