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A molecular dynamics study on wettability alteration of calcite nanopores by crude oil’s polar components

Advancements in horizontal drilling and hydraulic fracturing technologies have made hydrocarbon production from tight formations (e.g. carbonate, tight sand, and shale) an attractive alternative to conventional methods. However, understanding the fundamentals of multiphase flow in nanoporous media is a challenge due to potential non-Darcy effects during production. To better account for wall effects, which are important in nanoscale confinements, one should combine molecular simulations with pore-scale and meso-scale models. Very few molecular dynamic studies currently exist on multiphase flow in nanopores [1-3]. A major limitation of these studies is the fact that they used the course-grained approach, neglecting the electrostatic interactions involved in systems containing water and minerals.

The goal of this study was to investigate for the first time the flow of oil and brine in calcite nanopores and the impact of wettability alteration and pore geometry on flow using advanced molecular dynamics simulations and high performance computing. A flexible calcite model was adopted that accounts for both dissolution and precipitation and the force field parameters of Raiteri et al. [4] were employed. SPC/E model was used for water and the OPLS_AA force field was applied for the oil phase, which consisted of mixtures of asphaltene and resin model molecules in dodecane.

Fluid displacement was simulated by applying external forces on two pistons placed at each end of the fluids. The threshold capillary pressure (P_c^th) during drainage/waterflooding was determined as the pressure difference under which oil/water can no longer advance inside the pore. The displacement simulations were then performed under a pressure difference slightly greater than P_c^th and the oil/water/calcite dynamic contact angle (CA) was measured. The variation in P_c^th and CA during drainage and waterflooding was an estimate of wettability alteration. The effects of asphaltene and resin concentrations and their compositions on wettability alteration were examined.

References:
1) Sedghi, Mohammad, Mohammad Piri, and Lamia Goual. 2014. “Molecular Dynamics of Wetting Layer Formation and Forced Water Invasion in Angular Nanopores with Mixed Wettability.” The Journal of Chemical Physics 141 (19): 194703.

2) Chen, Chen, Lin Zhuang, Xuefeng Li, Jinfeng Dong, and Juntao Lu. 2012. “A Many-Body Dissipative Particle Dynamics Study of Forced Water–Oil Displacement in Capillary.” Langmuir 28 (2): 1330–36.

3) Stukan, M.R., P. Ligneul, and E.S. Boek. 2012. “Molecular Dynamics Simulation of Spontaneous Imbibition in Nanopores and Recovery of Asphaltenic Crude Oils Using Surfactants for EOR Applications.” Oil & Gas Science and Technology – Revue d’IFP Energies Nouvelles 67 (5): 737–42.

4) Raiteri, Paolo, and Julian D. Gale. 2010. “Water Is the Key to Nonclassical Nucleation of Amorphous Calcium Carbonate.” Journal of the American Chemical Society 132 (49): 17623–34.

Author(s):

Mohammad Sedghi    
University of Wyoming
United States

Mohammad Piri    
University of Wyoming
United States

Lamia Goual    
University of Wyoming
United States