ABSTRACT

Heavy oil is an immense oil resource that is untapped because its highly viscous nature makes it difficult to produce. Currently, the heavy oil reservoir production challenges are addressed by thermal recovery techniques, CHOPS, chemical injection and miscible gas injection. In this work, the advantages of three different processes viz thermal, chemical and miscible gas injection have been merged together to come up with a novel viscosity reducing process for heavy oil. Metal Nanoparticles are used for thermal conductivity enhancement of super critical-CO2 (sc-CO2) or "Viscosity reducing Injectant" (VRI) for reducing the viscosity of heavy oil rapidly as compared to conventional sc-CO2 or VRI. A sc-CO2soluble surfactant has also been added to the mixture to further enhance the viscosity reduction. Thus the thermal properties of metal nanoparticles, the chemical properties of surfactant and the miscible properties of sc-CO2 and VRI altogether reduce the viscosity of heavy oil.

INTRODUCTION

Crude oil is considered "heavy" if its API gravity is lower than 20 degrees. Heavy oil is asphaltic, dense, and viscous oil that is chemically characterized by its content of asphaltenes. In spite of an immense resource base, heavy oil and natural bitumen accounted for only about 3 billion barrels of the 25 billion barrels of crude oil produced in 2000 (U.S.G.S Fact Sheet 70–03, August 2003).

Currently, producers target heavy oil accumulations having better quality oil in terms of chemistry and density. About 66 percent of the heavy oil produced annually is lighter than 15° API gravity, but about 50 percent of the estimated technically recoverable heavy oil is denser (less than 15° API gravity, see Figure 1).

In conventional production, reservoir pressure from gas and water associated with the oil is generally sufficient to cause light oil to flow to a production well. However, to sustain commercial well production rates, heavy and extra-heavy oil production almost always requires measures to reduce oil viscosity and to introduce energy into the reservoir. When super-heated steam is injected into a reservoir, oil viscosity is reduced and reservoir pressure is increased through displacement and partial distillation of the oil. Steam may be injected continuously to form a flood or it may be injected in cycles so wells are used alternately for injection and production.

EOR, using miscible gas displacement, is a widely used technique and can increase the production of oil beyond what is typically achievable using the conventional recovery methods. Gas injectants are generally injected into the reservoirs either in immiscible or miscible condition. Miscible gas injection, where the gas becomes miscible with the reservoir fluid at reservoir temperature, is amongst the most widely used EOR process in the US today after thermal recovery processes, and it accounts for significant EOR oil production. (U.S.G.S Fact Sheet 70–03, August 2003).

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