Quantitative and Visual Characterization of Asphaltenic Components of Heavy-Oil and Bitumen Samples after Solvent Interaction at Different Temperatures and Pressures

摘要

Due to inefficiency of steam injection caused by technical, economic, and operational reasons, solvent methods have received special attention in heavy oil and bitumen recovery recentlyy. A solvent can be injected in the form of vapor extraction process at reservoir temperature. Hot solvent injection can be applied to improve the recovery rrate at lower temperatures than steam injection. These solvent driven recovery processes are quite complex on account of their “asphaltene destabilization” that takes place due to changes in temperature, pressure, and solvent dissolved in oil. As a result of this destabilization, the asphaltene precipitates, flocculates, annd eventually plugs the pores in the reservoir. In this research, the de-asphalting of a heavy oil sample was evaluated in a PVT cell with optical visualization. The experiments were undertaken at different temperature ranges (50?C to 80?C) and pressure (30psig to 500psig), which is the suggested range for hot solvent injection. Three light hydroccarbons (propane, n-hexane, and n-decane) were used as solvents. Applying standard SARA analysis (ASTM D2007 and ASTM D2549), the characteristics of the asphaltene precipitated at the bottom of the PVT cell, were determined quantitatively. Moreover, a methodology for “asphaltene precipitation concentration analysis” was developed in order to determine the effect the temperature, pressure, and solvent type had on asphaltene destabilization. This quantitative analysis was complemented through visual observations of asphaltene characteristics on the PVT cell as well as using optical microscopy. In addition, the refractive index measurements at the onset of precipitation were used to evaluate the changes in the oil after interacting with the solvent at different temperatures and pressures. Finally, a comparative analysis of the results was provided. Basedd on the quantitative and qualitative observations, the characteristics of asphaltene were classified in terms of their shape, size, and amount for different oil/solvent types, pressure, and temperature. This study will eventually lead to the identification of the effects of asphaltene characteristics on pore plugging during heavy-oil/bitumen recovery by gravity drainage from oilsands.