Abstract

There currently exists a large supply of heavy crude oils which are relatively uneconomical to produce. However, there are processes available which can be used in a downhole environment to upgrade them, resulting in significantly less sulfur and lowered densities and viscosities. A process which is especially favorable for downhole implementation is the use of in situ combustion to generate reactive upgrading gases, such as CO2 and to drive oil over a near-wellbore heated bed of catalyst. Two laboratory combustion tube runs were completed to test this concept. These differed from normal combustion experiments in that they employed a heated processing zone over which combustion gases and fluids passed prior to production. The first run used sand in the processing zone, and the second a bed of catalyst. The Middle Eastern heavy crude oil used was amenable to combustion, and the presence of a heated production-end processing zone did not affect the combustion performance. Passing oil and combustion gases over the catalyst prior to production resulted in substantial upgrading of the produced oil, including a 50% level of hydrodensulfurization and substantial decreases in oil gravity and viscosity. The catalyst efficiently converted CO2 generated at the combustion front, to H2, which then reacted with the oil to effect upgrading. The catalyst-bearing zone appeared to have a very low residual water saturation and was effectively oil wet, thus assuring that good oil-catalyst contacting occurred. However, it was found that the presence of a large amount of coke on the catalyst may indicate the need for periodic regeneration.

INTRODUCTION

Although there exists a large supply of heavy crude oil throughout the world, most of these reserves tie untapped for various reasons, chief among them being the poor economics of recovering heavy oils. The authors have recently described processes that could be used for significant downhole (in situ) upgrading of heavy crude oils1,2, despite previous reports which found that in situ processing has limited potential3. In situ processing has several advantages over conventional surface upgrading technologies. Because in situ upgrading can be implemented on a well-by-well basis, there is no needed for large capital-intensive projects. Rather, the size of an in situ project, for a particular field, can be tailored to available production rates; thus, upgrading is practical even for those fields deemed too small to provide sufficient production for conventional processing. Additional advantages for in situ upgrading include the production of a more desirable and valuable product, increased ease in shipping and pipelining, and less-demanding downstream processing.

The requirements for in situ upgrading include: provision for a downhole bed of catalyst, achieving appropriate reaction temperatures and pressures at the catalyst bed, and mobilization of oil and co-reactants over the catalyst. Although the technologies to accomplish each of these tasks are fairly well known, their combination into a unified process has yet to be demonstrated. A bed of catalyst can be placed by conventional gravel pack or proppant injection methods4,5.

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