Downhole Catalytic Process for Upgrading Heavy Oil: Produced Oil Properties and Composition
Authors: Greaves M. , Xia T.X. 
Published: March 2010

The level of in situ upgrading of heavy Wolf Lake oil achieved by a downhole catalytic process, which is a catalytic variant of the THAI process-"Toe-to-Heel Air Injection"-has been investigated using various analytical methods. These included gas chromatography (GC), elemental analysis, simulated distillation (SIMDIS), micro-activity test (MAT), plus density and viscosity. The tests were performed on the oil produced from the downhole catalytic upgrading process, which was conducted in semi-scaled 3D combustion cells. The tests employed a standard hydrogen de-sulphurisation (HDS) catalyst, which was "gravel packed" around the horizontal producer well, forming an annular radial inflow type reactor.

Although the analytical measurements made were necessarily selective in their scope, they nevertheless provide a good indication of what the potential may be for downhole upgrading in the field. Downhole catalytic upgrading produces a "light oil, " characterized by a low viscosity of around 60 mPas, or less. The produced oil is readily converted into gasoline and diesel fractions, with a higher conversion on an FCC basis than that obtained with normal virgin bitumen vacuum gas oil. Environmentally, there are also very significant potential benefits regarding in situ removal (and retention) of heavy metals, and reduction of sulphur in the oil.

Introduction

Fireflooding, in situ combustion (ISC), or heavy oil air injection (HOAI) is a process wherein a combustion front is propagated through the formation, vapourizing the oil and water ahead of it. Conventional forward combustion is a long-distance displacement process (Figure 1), so that vapourized oil and water are condensed in the cooler parts of the reservoir and are eventually produced from a producer well. Theoretically, forward combustion is intended to burn the least desirable fraction of the oil, leaving a clean formation behind. Its main drawback is that there must be sufficient mobility for the vapourized oil and water to be producedfter they have condensed ahead of the combustion front. This factor, frequently leading to loss of air injectivity and consequent inability to maintain the process in a high temperature oxidation (HTO) mode, has probably been responsible for the poor performance, or failure, of many field applications of the conventional ISC process.

Short-distance displacement (Figure 1) is a concept that was made possible by the development of horizontal well technology. SAGD (steam-assisted gravity drainage) is the most well-known thermal process in this category. THAI-"Toe-to-Heel Air Injection," is an integrated horizontal wells-thermal process, also fitting into the short-distance displacement category (Figure 1), but with some unique features. Briefly, there is no necessity for communication into, or displacement through, the oil layer downstream of the combustion front. Rather, this is excluded by THAI, since the cold heavy oil region downstream of the combustion front provides a natural "barrier" by virtue of its very high viscosity, as well as providing a seal around the horizontal producer well. Figure 1 illustrates the "moving window" effect in THAI, due to the propagation of the combustion front.