# Parametric study

A parametric study is carried out to investigate the influence the inlet and the outlet on the oil recovery ratio. For the same geometry, the parametric study investigates:

- the influence of the position of the inlet/outlet

- the influence of the size of the inlet/outlet

- the influence of the initial quantity of oil in the domain

The objective is to observe if the inlet and the outlet have a major impact on the flow behavior and which configuration would provide the greater oil recovery ratio.

Simulations are carried out with Fluent at a velocity inlet of 0.6m/s, using real physical properties and a first order explicit scheme.

The oil viscosity value is increased in order to reduce convergence issues and to help Fluent to handle topology changes. Indeed, as a crude oil viscosity value can vary from 1 to 1000mPa.s,  the oil viscosity  is increased to 420mPa.

# Optimization of gas injection

The first part of the parametric study investigates how the position and size of the injection well can influence the results.

Two positions are tested, on the bottom and lateral  wall of the domain, with an intlet lenght constant equals to 0.025m. Then the size of the inlet is reduced by two as it is shown in the pictures below:

Simulation parameters are listed in the table below:

 Velocity Inlet Percentage of gaz injection Percentage of oil recovered Inlet 1 0,6 m/s 75% 68,5% Inlet 2 0,6 m/s 75% 77% inlet 3 1,2 m/s 75% 66%

The graph below represents the percentage of oil in the domain in function of time. We can observe that after injecting 70% of gas in the domain, the quantity of oil remains constant: the oil recovery ratio is maximum. There is a maximum quantity of gas injected after which oil viscosity ratio can not be increased.

After an injection of 75% of nitrogen, the same amount of oil is recovered in the case of Inlet 1 and 3 . Therefore, the size of the injection well does not  influence the oil recovery ratio.

On the contrary, the percentage of oil recovered by Inlet 2 is increase by 12.6% compared to Inlet 1. The position of Inlet 2 is more efficient than the position of Inlet 1 to recover oil. Thereforethe position of the injection well have an impact on the oil recovery ratio.

We recommand to investigate carefuly the position of the injection well before developping the nitrogen injection recovery method in the Tarim Basin, as it impacts the oil viscosity ratio.

# Influence of the outlet

The influence of the oulet is also investigated. Indeed, connexions between caves can be completly differente. Thus, it is important to see how the flow behaves for a different outlet.

Two positions are tested, with an outlet lenght of 0.05m. Then,  the size if the outlet is increased by two as it is shown in the pictures below.

In these configurations, the inlet is the same used in the reference geometry.

Simulation parameters are listed in the table below:

 Velocity Inlet Percentage of gaz injection Percentage of oil recovered Outlet 1 0.6 m/s 75% 68,5% Outlet 2 0.6 m/s 75% 69% Outlet 3 0.6 m/s 75% 70%

The graph below represents the percentage of oil in the domain in function of time. We can observe that after injecting 75% of gas in the domain, the quantity of oil remains constant: the oil recovery ratio is maximum. There is a maximum quantity of gas injected after which oil viscosity ratio can not be increased.

After an injection of 75% of nitrogen, the same amount of oil is recovered in the case of Outlet 1, 2 and 3 . Therefore, the size a,d the position of the injection well does not  influence the oil recovery ratio.

# Influence of the initial amount of oil

Finally, the parametric study investigates how the initial quantity of oil in the domain can influence the results.

Two simulations are carried out: one with the size of the inlet is reduced by two as it is shown in the pictures below:

37% of  oil initialy in the domain                                18% of  oil initialy in the domain

Simulation parameters are listed in the table below:

 Velocity Inlet Percentage of gaz injection Percentage of oil recovered 37% oil initial 0.6 m/s 75% 78% 18% oil initial 0.6 m/s 75% 66.5%

After an injection of 75% of nitrogen, the percentage of oil recovered in function of the initial quantity of oil is higher when the initial quantity of oil is important.

These results were expected as every recovery method have difficulties to recover oil when the initial quantity is really small.

Therefore, the initial amount of oil in the domain impact the efficiency of the recovery method. The oil recovery ratio will not be the same for every cave and will depends on the initial amound of oil present in the cave.