Discontinuous Displacement at Solvent–Immobile Hydrocarbon Interfaces

Abstract

Concerns over the environmental impacts of thermal production methods for bitumen and heavy oil have led to the exploration of alternative technologies including solvent-assisted production methods. While solvent-assisted production methods have been studied extensively, apparent diffusion rates of the penetrating solvent one to two orders of magnitude greater than those predicted from the Fickian diffusion are required to match production histories. “Surface renewal” and “sloughing” mechanisms have been suggested to explain such abnormally high solvent penetration rates during production but have not been observed directly or included in process models. In this work, high-resolution X-ray videography is employed to investigate solvent penetration at interfaces between a model solvent (n-pentane) and a model immobile reservoir fluid (octacosane) over time and observe “surface renewal” and “sloughing” directly for the first time. Solvent and wax are sealed in shell glass vials in contact with each other creating solvent-wax interfaces. Various solvent-wax interfaces, including the horizontal interface with the wax below, horizontal interface with the solvent below, as well as the vertical interface, are studied. The interface progressions are analyzed by using the software ImageJTM to track intensity changes over time. The experimental results show that for horizontal interfaces (octacosane below), interface displacement arises solely from diffusion and rates of displacement are slow (~ 10-2 µm/s). For vertical pentane-octacosane interfaces and horizontal pentane-octacosane interfaces (pentane below) steady displacement rates, an order of magnitude greater than for diffusion alone, are punctuated by rapid detachments of ~ 30 µm layers of octacosane-enriched liquid from the interface at ~ 150 s intervals. For vertical interfaces, that dominate production processes especially in thin reservoirs, average interface displacement rates approaching 1 µm/s are realized. These findings highlight the impact of interface orientation on interface displacement rate. They also provide quantitative insights into the kinetics of solvent-assisted bitumen and heavy oil production processes in high-permeability reservoirs, needed as inputs for modeling “surface renewal” and “sloughing” mechanisms directly in these processes.