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Pore-scale Simulation of the Effect of Pore Geometry and Surface Heterogeneity on Oil Recovery by Low-salinity Water Flooding

Ahmadi Falavarjani, Ali | 2023

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 56112 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Mahani, Hassan; Ayatollahi, Shahabodin
  7. Abstract:
  8. Low-salinity waterflooding (LSWF) is a promising EOR approach that decreases the oil-wetness of reservoir rocks, hence increasing the recovery factor. Despite the importance of the pore-geometry on the performance of LSWF, especially in 3D simulations being affected by corner-flow and roughness, it is not yet investigated, thus in this thesis we aim at studying the aforementioned effects on LSWF. According to the preceding studies, during the drainage phase, the brines in the corners of pores cannot be displaced by oil because of requiring very high capillary pressure; thereby rendering a mixed-wet system. Hence considering this type of wettability is necessary for two-phase flow investigations. In this study, we have evaluated the effect of corner flow and surface heterogeneities (roughness) on the secondary mode of LSWF by direct numerical simulations using OpenFOAM (Open-Source Field Operation and Manipulation) in 2D and 2.5D (quasi-3D) pore-scale models. For this purpose, two models were designed: a simple homogeneous model to investigate the flow regime during LSWF under the influence of corner-flow compared with a 2D version of this geometry which lacks the effect of corner-flow. The second model with a higher level of heterogeneitey (a quarter of five-spot model) was selected to probe the validity of the results of the first model and to investigate the effects of the kinetics of wettability alteration on LSWF performance. In this geometry, we studied the polymer-enhanced LSWF as well. To mimic the initial fluid distribution of reservoirs and observe the corner flow phenomenon, first drainage (displacing water by oil) simulations was performed. After the steady-state condition was achieved, wettability of the regions in contact with oil was altered to oil-wetting state and a system with mixed-wettability was developed. The simulations were then continued by secondary LSWF under capillary-dominated regime (capillary number equal to or less than 10-5). Therefore, in this study a more realistic output of the two-phase flow behavior is presented by incorporating various features of pore-geometry into our model. Based on the findings of this study, since low-salinity (LS) brine is able to move ahead of the primary flow front due to the corner flow, wettability alteration may occur in front of the oil-water primary interface leading to a faster oil relocation and/or oil entrapment by blockage of the oil production path and also through the snap-off process. In this regard, an interplay between corner flow and surface heterogeneities is observed, through which LS water that is flowing in the corners, after wettability alteration (WA) of the oil-wet surfaces, can imbibe along the surface roughness of grains leading to oil break-up (via snap-off) which increases the residual oil saturation. According to the overall outcomes of the simulations, it is concluded that the interplay between the aforementioned phenomena and the time dependency of wettability alteration (kinetics) may adversely affect the LS injection efficiency. Therefore, there will be an optimum point (condition) for LSWF which is assumed to be a function of kinetics of WA and the dispersion of low-salinity water due to the corner flow. Polymer-enhanced LSWF, to some extent may reduce these negative effects in particular the snap-off occurrence during LSWF. The results of this study present a better understanding of the dynamics of two-phase flow in porous media, which can be used to optimize LSWF efficiency in mixed-wettability systems and can potentially explain the failure or success of LSWF results observed in the experiments
  9. Keywords:
  10. Direct Numerical Simulation (DNS) ; OpenFOAM Software ; Low Salinity/Smart Waterflooding ; Mixed Wettability ; Pore-Scale Model ; Surface Heterogeneity (Roughness) ; Corner-Flow ; Pore Geometry

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