Dynamic Behavior of Asphaltene Precipitation and Distribution Pattern in Carbonate Reservoirs During Solvent Injection: Pore-Scale Observations
Authors: Telmadarreie Ali , Trivedi Japan 
Published: February 2017

Precipitation and deposition of asphaltene in reservoir rock can cause formation damage and reduce the fluid mobility, resulting in significant loss of the 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. Carbonate reservoirs in Western Canadian Sedimentary Basin (WCSB) have several challenges for enhanced oil recovery process (i.e. heterogeneity, the high viscosity of oil). Asphaltene-induced formation damage makes it more difficult for any process to recover heavy oil from such complex reservoirs.

For advancements in understanding asphaltene deposition in fractured carbonate formations, asphaltene deposition behavior was analyzed with the help of pore scale observation during hydrocarbon solvent injection. Three types of solvent (nC5, nC7, and nC12) were used for solvent injection for extra-heavy oil recovery (30,000 cp at 22 °C). A uniquely designed heterogeneous-fractured micromodel imitating the fractured carbonate reservoirs was used for pore scale 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. By increasing carbon number of solvent from C5 to C12, the amount of precipitation decreased while the wider distribution of deposited asphaltene was observed in a fractured-heterogeneous porous media. 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 deposit perpendicular or parallel to the flow direction which is in the form of parallel rope-shape deposits. The perpendicular deposits (usually in dominant diffusion flow), mainly observed in small pore throat, can block the diffusion path. However, the parallel shape 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 carbonate reservoirs such as; susceptible locations of asphaltene deposition, different types/shapes of deposition which may or may not result in pore blocking, and effect of flow behavior and heterogeneity on asphaltene deposition and formation damage. The more we know about the asphaltene deposition in such heterogeneous reservoirs, the better we can control the formation damage and increase the effectiveness of heavy oil recovery processes.