Engineered waterflooding modifies chemistry of injected brine to efficiently and environmentally friendly enhance oil recovery. The common practice of engineered waterflooding includes low salinity waterflooding (LSW) and carbonated waterflooding. Among these oil recovery methods, wettability alteration has been perceived as a critical physicochemical process for additional oil recovery. While extensive work has been conducted to characterize the wettability alteration, the existing theory cannot explain the conflict oil recovery between secondary mode (injecting engineered water at the very beginning of flooding) and tertiary mode (injecting engineered water after conventional waterflooding), where secondary engineered waterflooding always gives a greater incremental oil recovery than tertiary mode. To explain this recovery difference, a preferential flow channel was hypothesized to be created by secondary flooding, which likely reduces sweep efficiency of tertiary flooding. To test this hypothesis, computational fluid dynamic simulations were performed with finite volume method coupled with dynamic contact angles in OpenFOAM to represent wettability characteristics (from strongly oil-wet to strongly water-wet) at pore scale to quantify the role of pre-existing flow channel in the oil recovery at different flooding modes. The simulation results showed that secondary engineered waterflooding indeed generates a preferential flow pathway, which reduces recovery efficiency of subsequent tertiary waterflooding. Streamline analysis confirms that tertiary engineered waterflooding transports faster than secondary engineered waterflooding, implying that sweep efficiency of tertiary engineered waterflooding is lower than secondary engineered waterflooding. This work provides insights for a greater oil recovery at secondary mode than tertiary mode during engineered waterflooding at pore scale.
In this paper, the finite volume method was used to numerically study the
heat transfer and flow of double-pipe heat exchangers(DPHE)under static and
ocean motion conditions. The ocean motion is simplified as a harmonic
oscillation with the center of the DPHE as the axis of rotation. In addition
to the flow direction and the inlet Reynolds number, the effects of amplitude
and period on total heat transfer coefficient, pump power and thermal
performance factor were also analyzed quantitatively. The results showed that
as the heat exchanger oscillates, the total heat transfer coefficient and pump
power exhibit a periodic change and the period is half of the oscillating period
of the heat exchanger. The total heat transfer coefficients for all oscillating
DPHEs are higher compared to static conditions, reaching a maximum improvement
of 9.84% at low Reynolds numbers. The total heat transfer coefficient and pump
power of DPHE under oscillation are significantly regular, positively
correlated with amplitude and negatively correlated with period. When the
amplitude exceeds 0.5 rad/s, the oscillatory condition has thermal
performance improvement for the oscillating DPHE with the inner tube with low
Reynolds number and the outer tube with high Reynolds number. In the optimum
condition, the thermal performance of the inner and outer tubes is improved by
5.01% and 1.48%, respectively. The thermal performance coefficient of DPHE
hardly changed when the period exceeded 5s.The results here in provide a
theoretical basis for predicting the development of off shore double-pipe heat
exchange equipment.
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