Dynamic Behavior of Asphaltene Deposition and Distribution Pattern in Fractured Porous Media during Hydrocarbon Solvent Injection: Pore-Level Observations

Precipitation and deposition of asphaltene in reservoir rock can cause formation damage and reduce the fluid mobility, resulting in significant loss of hydrocarbon production. A detailed study on asphaltene deposition behavior in porous media improves the understanding of asphaltene-induced formation damage and provides the possible solutions for preventing and/or controlling formation damage. For advancements in understanding asphaltene deposition in fractured porous media, asphaltene deposition behavior was analyzed with the help of pore level observations during hydrocarbon solvent injection. Three types of hydrocarbon solvents (nC5, nC7, and nC12) were used for solvent injection for extra-heavy oil recovery (30 000 cP at 22 degrees C). A uniquely designed heterogeneous-fractured micromodel imitating the fractured porous media was used for pore level observation. A high-quality camera along with a microscope was utilized to capture images. SEM analysis was also performed on precipitated asphaltene to visualize the difference in the structure of the asphaltenes precipitated with different solvents. Observation through this study revealed that besides the amount of asphaltene deposition, the distribution pattern of asphaltene deposition could also be different when using various types of solvent. Besides decreasing the amount of asphaltene precipitation, the deposited asphaltene distributed more widely in the studied porous medium as carbon number of solvent increased (C5-C12). Moreover, it was noted that asphaltene could be deposited in different shapes that may or may not block the pore throat. The dominant flow mechanism (either diffusion dominant or viscous dominant) will affect the shape of deposited asphaltene. Asphaltene can be deposited perpendicular or parallel to the flow direction, which is in the form of parallel rope-shaped deposits. The perpendicular deposits (usually in dominant diffusion flow), mainly observed in small pore throat, can block the diffusion path. However, the parallel deposits (typically in viscous dominant flow) will not significantly impede the flow path. The results of this study improve our understanding of different aspects of asphaltene-induced formation damage in the fractured reservoirs such as susceptible locations of asphaltene deposition, different shapes of deposition which may or may not result in pore blocking, and the effect of flow behavior and heterogeneity on asphaltene deposition and formation damage.