PVT Analysis [Shale Fluid Systems]

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PVT

PVT: Individual Services Analysis

Sampling
Separator oil and separator gas samples are taken on location, directly from the separator.
Sampling Personnel Charge
Transportation Charge


Compositional Analysis
The compositions of the separator gas and separator oil are determined by gas chromatography. The molecular weight of the separator oil is determined by cryoscopy. The recombined reservoir fluid composition is calculated using the measured separator compositions and the separator GOR. Molecular weights of the separator oil plus fractions are calculated.

 

Recombination of Separator Fluids

The separator to stock tank shrinkage factor for oil is obtained by flashing a known volume of separator oil at separator conditions to stock tank conditions. This shrinkage factor is then used to convert the produced GOR to separator GOR. Using the separator GOR, the separator fluids are recombined in a PVT cell at reservoir temperature and pressure and mixed until a single phase is achieved.


Density and Viscosity Measurement

The density and viscosity of the recombined reservoir fluid are measured at reservoir temperature and a range of pressures, both above and below the bubble point. These measurements are performed using a high pressure densitometer and viscometer.


Constant Composition Expansion

The recombined reservoir fluid is loaded into a PVT cell at reservoir temperature and a pressure higher than the bubble point. The total fluid volume is measured as pressure is reduced in steps. The total volume is plotted against pressure for determination of the saturation pressure. Properties reported from this test include Saturation Pressure, Y-function, and Single Phase Compressibility.

 

Differential Liberation Expansion

The recombined reservoir fluid is loaded into a visual PVT cell at reservoir temperature and saturation pressure. The pressure is lowered, and evolved gas is measured at cell pressure and temperature, as well as standard conditions. The gas is then evacuated from the cell while maintaining the current cell pressure, and keeping the observed gas-liquid interface in the visual cell window. The composition of the evacuated gas is measured by gas chromatography. This process is repeated until the cell pressure reaches the atmospheric value. Properties reported from this test include Solution GOR, Relative Oil Volume, Relative Total Volume, Deviation Factor, and Gas Formation Volume Factor.


2-Stage Flash Separator Test

In the first stage, a volume of recombined reservoir fluid is flashed from reservoir conditions to separator conditions. After the fluid reaches equilibrium, the volumes of gas and liquid are measured. Gas composition is then measured by gas chromatography. In the second stage, the first-stage separator oil is flashed from separator conditions to stock tank conditions. The volumes of oil and gas are measured. The composition of the second-stage gas is measured by gas chromatography. This test is performed at various conditions for separator optimization. Properties reported from this test include GOR, API Gravity of stock tank oil, Formation Volume Factor, and Separator Oil Shrinkage Factor.

PVT

Complete PVT Study

The complete PVT study includes all of the aforementioned services.
Complete PVT Study
Sampling Personnel Charge
Transportation Charge

 

Slim Tube Test (MMP)

The separator to stock tank shrinkage factor for oil is obtained by flashing a known volume of separator oil at separator conditions to stock tank conditions. This shrinkage factor is then used to convert the produced GOR to separator GOR. Using the separator GOR, the separator fluids are recombined in a PVT cell at reservoir temperature and pressure. A 40 ft sand packed slim tube equipped with a high-pressure glass capillary and a dome loaded back pressure regulator is used for the multiple contact miscibility study. The porosity of the sand pack is 35% and the permeability is approximately 1.5 Darcy. The cleaned slim tube is saturated with toluene. The back-pressure is set at the desired test conditions and the toluene is displaced by a minimum of 2 pore volumes of crude oil before each displacement test. The CO2 is injected at constant rate of .125 cc/min using a motorized high pressure pump. The oil produced in the separator at the end of the test is recorded and the oil recovery as function of the original oil in place is calculated. The data is plotted, the lines representing recovery versus pressure below and above the MMP are identified. The intersection of these two lines represents the MMP.

Minimum Miscibility Pressure Determination
Sampling Personnel Charge
Transportation Charge

 

 

 

 

 

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