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

Abstract

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.