Effect of Crude Oil Composition on Microwave Absorption of Heavy Oils

Abstract

Heat generation in the reservoir by means of electromagnetic wave stimulation offers innate advantage with efficient energy introduction. Transmissibility of heavy oil and bitumen are predicated on decreased viscosity through temperature rise, which makes microwave heating a plausible candidate. This study focuses on identifying the components of the crude oil which primarily contribute to heat generation under the influence of the microwave. Pinpointing what makes the oil a more effective microwave receptor enables the optimization of desirable traits in the oil phase. Three different oil samples were selected due to variations in both physical and dielectric properties. Fractionations were then performed on each oil to isolate the contribution of each SARA (saturates, aromatics, resins, and asphaltenes) constituent. Dielectric constant and loss index, which together represent complex permittivity, were measured by utilization of a vector network analyzer (VNA) with a dielectric probe. Complex permittivity of both the bulk oil as well as each fraction were measured for all three oil samples. Also, investigation into asphaltenes behavior in the oil, either precipitated or dispersed, was performed by introducing varying dosages of both precipitating agents (nC5, nC7) and a dispersant (toluene). Within the oil phase, the mutual attraction that is realized by the more polar components, namely the resins and asphaltenes, creates complexities in the absorption behavior. Net cancellation of the individual polarity is evidenced by the non-additive nature of the deasphalted oil and asphaltenes. The attraction between the resins and asphaltenes is further illuminated by inspection of the dielectric response in the presence of the precipitating agents. Removal of asphaltenes through precipitation corresponds to the freeing of interacted resins. The contribution in polarity of the previously cancelled resins is evidenced by an increase in the dielectric constant with increasing precipitating dosage. Both oil C2 and C3 achieve the identified behavior stemming from an asphaltene weight percent comparable to that of the resins. However, upon analysis of the oil C1, the opposite trend is achieved. Unique to oil C1 is a very large weight percent of asphaltenes. Therefore, the oil has excess asphaltenes which aren't interacting with the resins. Precipitation preferentially occurs from those asphaltenes not being interacted as they are relatively less stable. Net cancellation of all resins remains untouched and no resins are freed as a function of the precipitation for oil C1. The foundational impact of polarity on absorption characteristics provides the potential to investigate the efficacy of microwave introduction specific to each fractionation. Experimental results from dielectric property measurements showed that the polar fractions of the crude oil, resins and asphaltenes, heavily influence the effectiveness of microwave heating. For the first time, the contribution of individual SARA fractionations to microwave efficiency was investigated.