Page 85 - Enhanced Oil Recovery in Shale and Tight Reservoirs

72 Enhanced Oil Recovery in Shale and Tight Reservoirs

respective Winprop and GEM simulators developed by Computer
Modeling Group.
The Winprop simulator uses the asphaltene precipitation model pro-
posed by Nghiem et al. (1993). The model splits the heaviest component
into two components: the nonprecipitating component and precipitating
component. The two components have the same critical properties and
acentric factors but different interaction coefficients with light components.
The precipitating component has relatively larger interaction coefficients
with light components, which leads to greater incompatibility between
the precipitating component and the light components. As a result, the
precipitating component will transfer to a solid phase, and thus precipitate.
The nonprecipitating component includes heavy paraffin, resins, asphal-
tene/resin micelles that will not dissociate. The precipitating component
is asphaltenes and asphaltene/resin micelles that could dissociate and precip-
itate. The precipitating asphaltene component in crude oil is considered as a
pure dense phase which can either be a liquid or solid. This phase is referred
to as the asphalt phase.
Shen and Sheng (2018) lumped together 24 components of an oil into
five pseudocomponents: C 3 4 ,C 5 8 ,C 9 19 ,C 20 40 ,C 41þ . The heavy
precipitating component was C 41 asphaltene . The interaction coefficients of
the split precipitating asphaltene component with the light components
and the molar volume of asphaltene phase were tuned to match the asphal-
tene precipitation data from the model with the experimental data. The
tuned parameters are listed in Table 3.1. The predicted asphaltene precipi-
tation data and the experimental data are compared in Fig. 3.13. The molar
volume of precipitating asphaltene component was tuned to be 0.92 L/mol.
The GEM simulator uses the asphaltene deposition model developed by
Wang et al. (1999):

vE A
¼ aC A f bE A ðv L v Lc Þ þ gu L C A (3.1)
vt
The first term on the right side of the above equation is the surface depo-
sition. a is the surface deposition rate coefficient that should be a positive

Table 3.1 Binary interaction coefficients between asphaltene component and other
components used in the precipitation model.
Components CO 2 CH 4 C 3L4 C 5L8 C 9L19 C 20L40 C 41D C 41 asphaltene
0.27 0.2 0.2 0.04 0 0 0 0
C 41 asphaltene