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Reservoir Fluids

Enhanced Oil Recovery - EOR


Forward Multi-Contact

A known volume of reservoir fluid is charged to a high-pressure PVT cell and heated to the reservoir temperature. A measured portion of the injection gas is injected to the cell. The quantity of injection gas is expressed in terms of mole fraction of injection gas as a fraction of total moles in place at the start. The cell contents are pressurised and the contents thoroughly mixed and stabilised in single phase (dependent upon the saturation pressure of the mixture and maximum working pressure of the PVT cell). The mixture is then re-stabilised at the selected test pressure for 24 hours. At this pressure gas and liquid equilibrium phases are formed and the total volume of sample measured.

The equilibrium contact gas phase composition and density are determined.

The composition of the equilibrium contact gas phase is used in conjunction with the correlations of Lee, Gonzales and Eakin to calculate the equilibrium gas phase viscosity at the selected pressure at reservoir temperature.

The remaining gas is then displaced from the PVT cell. The total volume of gas is now known from the total volume pumped from the cell. The liquid volume is equal to the total volume minus the gas volume. During this process the liquid volume can also be visually measured as a cross check.

EOR - Forward Multi-Contact

A partial pressure-volume relation is performed on the liquid phase to confirm the saturation pressure used for the equilibrium contact phase separation. The density and composition of the liquid phase is determined from the cell at a pressure above the contact pressure. The density at saturation pressure is then calculated using the measured relative volumes from the above partial pressure-volume relation.

The viscosity on the liquid phase is performed using a high pressure Electro Magnetic Viscometer at reservoir temperature.

The first contact is between the gas recovered from the original equilibrium contact mixture (usually the final gas addition of the swelling study) and original reservoir fluid. A known volume of reservoir fluid is mixed with the known volume of gas in a second PVT cell and stabilised in single phase. The mixture is then re-stabilised at the selected test pressure for 24 hours and the volumes, compositions and densities of each phase and the viscosity of the liquid phase determined as described previously.

This procedure is repeated using the gas recovered from the previous contact and the original reservoir fluid until the volume of gas formed at the selected test pressure is insufficient for any analyses. When it is determined that this point has been reached a final contact is carried out with sufficient reservoir fluid to produce a mixture which remained in single phase at selected test pressure. The composition and density of the final mixture are determined.

As an internal quality check for each contact a mass and molar balance is performed. The mass and moles of fluid in place are calculated using the densities, molecular weights and volumes of gas and oil contact mixed together. The densities, molecular weights and volumes of gas and oil phases (at the selected test pressure) are then used to calculate the mass and moles and therefore total mass and moles in place. The values are compared and should be within 2%.