Upgrading Athabasca Tar Sand Using Toe-to-Heel Air Injection

Abstract

The unique operation of the THAI (Toe-to-Heel Air Injection) process, enables very high oil recovery and substantial in situ upgrading. Both thermal upgrading (non-catalytic) and also catalytic upgrading, in which a catalyst is emplaced along the horizontal producer well, were investigated. 3D physical model experiments were conducted on virgin Athabasca tar sand bitumen to investigate dry and wet combustion performance. These results were compared against those from a steamflood test, which was subsequently followed by air injection. Excellent ignition, very stable combustion propagation and thermal upgrading of nearly 10 ° API were achieved using Athabasca tar sand. Additional upgrading was achieved using an in situ catalyst. THAI has the extra advantage that some hydrogen is generated in situ, providing further significant upgrading via hydroconversion. There are also substantial environmental benefits because of the large reductions in sulphur and heavy metals in the produced oil. Furthermore, oil is produced without "displacement delay," immediately ahead of the combustion front. The oil recovery using THAI was greater than 75% OOIP. Introduction The world's conventional crude oil production is expected to reach its peak in the second decade of this century and enter a permanent decline phase(1). The composition of the oil barrel is getting heavier, and diluent blending "stop-gaps," assisted by very limited coker upgrading capacity will, eventually, be insufficient to cope with the increasing demand for light oil. Historically, heavy oil trades at a substantial discount to that of premium light crude oil. Therefore, it has lower economic value and also market potential, unless new technology is developed to upgrade it to lighter oil, in an economic manner. The Athabasca Tar Sand deposit of northeastern Alberta, Canada, is one of the largest reserves of bitumen in the world. These are estimated to be 212.9 ??109 m3 (1,339 ?109 bbl)(2). Although about 10% of the bitumen reserves are mineable, the rest of the Athabasca Tar Sands have to be exploited by in situ recovery technology. A number of in situ oil recovery methods, such as steam assisted gravity drainage (SAGD)(3) and in situ combustion (ISC)(4, 5), have been extensively studied, both in the laboratory and in field tests. In situ combustion (ISC) is a thermal EOR method, in which a small fraction of the oil (or coke) in the oil layer is burned in order to mobilize the unburned fraction. Due to the strong exothermic oxidation reactions between hydrocarbon (or coke) and oxygen, the temperature of the oil-bearing matrix in the combustion zone is 500 to 700 °C, which is much higher than in steam flood processes (150 to 250 °C). High temperatures are very favourable for tar sands and heavy oil reservoirs, because not only is the oil viscosity reduced by several orders of magnitude, but the heavy residue is also thermally cracked to lighter compounds.

Dynamic Simulation of the Toe-to-Heel Air Injection Heavy Oil Recovery Process

“…Further, Xia and Greaves 8 did not report any problem of this sort during the experiment. However, because the dry combustion experiment lasted for only another 10 minutes (to 320 minutes), it is impossible to conclude this with any certainty.…”

“…The findings from a 3D THAI experiment, using natural, virgin Athabasca bitumen, as reported by Xia and Greaves 8 , has been used to validate the model developed in this work.…”

“…The frequency factors and activation energies for Reactions 3 and 4 were 'tuned' using a trial and error search, in order to match the experimental parameters reported by Xia and Greaves 8 .…”

“…Thus THAI is a gravity-stabilised process. Experiments [8][9][10][11] , and also field scale developments 12 , have consistently demonstrated robust and stable combustion front propagation. Turta and Singhal 13 , Xia et al 11 , and Greaves et al 14 have highlighted the advantages of THAI as a heavy oil recovery technique over conventional ISC and Steam Assisted Gravity Drainage (SAGD).…”

Laboratory screening tests on the effect of initial oil saturation for the dynamic control of in-situ combustion

“…The chemical reactions occurring at elevated temperatures during ISC lead to the production of a better quality oil than the original oil [12][13][14]. Therefore, the upgrading mechanism is accomplished through cracking reactions and the hydrocarbons at gas-state at the cracking region temperatures condense at adequate temperature ranges while traveling towards the production end [3,14].…”