PanTerra will assist the customer in the preparation of wells for sampling. PanTerra sampling engineers will collect the separator samples using piston and gas cylinders. If required, H2S inert cylinders will be used. A basic quality control check will be done on-site, measuring opening pressures and sample volumes. H2S and Mercaptan content can also be measured onsite.

The reservoir fluid is flashed in a controlled environment into vapor and liquid components. The flashed oil and gas volumes, separation temperatures and atmospheric pressures are accurately recorded. The resulting fractions are analyzed using the gas chromatography procedure. The gas and oil compositions are recombined on a mass basis.

The separator oil and gas samples are recombined in the laboratory using the separator GOR or a target bubble/dew point to re-create the original reservoir fluid. Once the mixture is stable, a flash procedure will be run to certify the composition.

The experiments performed are Constant Composition Expansion, Differential Liberation, Separator Tests, Constant Volume Depletion and Viscosity studies. The Constant Composition Expansion employs expanding a known amount of sample from the chosen cylinder in the PVT cell, from the working pressure to ambient pressure at reservoir temperature, with sample volumes measured at each step. The data generated from the experiment is: thermal expansion, saturation pressures, relative volumes, compressibility, Y factor, density at various pressures and reservoir temperature. During the Differential Vaporisation experiment, the analysis will be carried out at reservoir temperature to simulate the volumetric and compositional changes in the reservoir during production. The fluid is charged to a cell at reservoir conditions then expanded stepwise down to atmospheric conditions, with the gas liberated at every step. The output includes GOR, Relative Oil Volume, FVF, gas gravity, gas compressibility factor and liquid density. The Separator Tests are run at stages of temperature and pressure as requested by the client. The fluid at bubble point pressure is flashed from a PVT cell into a separator unit at the first stage conditions. Once the sample is stable, the gas is removed from the cell. The resulting data includes gas volume at Pstage and Tstage, gas volume at standard conditions, separator solution gas oil ratio, Z-factor and relative oil volume at Pstage and Tstage. The Viscosity studies involve fluids charged to an electromagnetic viscometer measurement chamber and then depressurized stepwise. Two coils inside the EMV magnetically force a piston back and forth. Viscosity values are calculated as a direct function of the piston round travel time. The Constant Volume Depletion experiment simulates the behavior of the gas condensates in the reservoir during production.

A mole % gas/liquid ratio will be recommended by the client. The working pressure selected will be higher than the highest expected saturation pressure. An amount of reservoir gas corresponding to a n% molar ratio to the liquid is mixed thoroughly in the PVT cell with reservoir oil, until completely dissolved. The sample is then stabilised above working pressure. A bubble point measurement is then performed on the swollen sample. The volume reading is taken a Pwork and Tres. The procedure is repeated adding increments of m% mole reservoir gas, i.e. the total amount of gasto be dissolved is n, n+m, n+2m etc. The composition of the fluid at every swelling stage in calculated, having as an input the composition of the original reservoir oil and the injection gas. The final data includes the bubble points at each stage (pressure required to dissolve the stage gas), stage relative volume and swelling factor Xs (stage saturation volume relative to the original reservoir fluid volume at saturation pressure),stage GOR, stage composition, densities at bubble point.