Differential Liberation Test


The above figure represents the schematic of the differential liberation test. The test is conducted through the use of oil mixtures.

  • At the first phase of the test based on the diagram above, the fluid needs to be constantly at the room temperature which is known as reservoir temperature of the supplied chain.

  • As the experiment is on the process, the differential liberation test is designed to have value on top purposefully to allow depletion of gas.

  • It is the saturation pressure or above that enables the experiment to take place.

  • The next phase, the reducing of volume is observed in each step hence it’s a requirement to note down the corresponding values of volumes and pressure at each step.

  • The observation of the formation of gases bubbles that is incipient indicates that the saturation point of the experiment has been obtained.

  • During the procedure, gases undergo depletion at every pressure stage before attaining saturation.

  • An equation is developed to determine the compressibility aspects of gas at the cell condition which based on the formula
    Paraphrasing 1

  • The formula
    Paraphrasing 2is applicable to measure the quantity of the collected gas in a standard condition and identify the gas formation aspects

  • The stages of conducted experiment involving ratio of gas/oil is calculated summing up the rated quantity of the liberated gas liberated in all segments of ongoing experiment hence dividing the total of the gas quantity by the residual quantity of oil.

Applications of the Differential Liberation Test

  • The agenda of conducting the any PVT experiment is to understand the way reservoir fluids react at the reservoir conditions.

  • The secondary generated information from the differential Liberation Experiment especially in volumetric changes in well stream in standard condition is essential for use.

  • Another essential element positioned at the differential liberation is the quantity measured in the solution of the gas/oil ratio, RS.

Flash test

  • The first phase of the flash test is to change the oil sample into the PVT cell through standardize resiouviour temperature based on its bubble point pressure.

  • A measurable sample of oil, of volume (Vo)pb is evacuated from PVT after which the cell at stated pressure is removed using a multi-stage separator object. The process is maintained at a standard temperature and pressure

  • The gas which is released from the segments of separator is measured and noted down based on its identified gravity and volume. The additional oil quantity at last phase indicated as (Vo)st.

  • The sum of the collected solution gas to oil ratio, oil formation aspect for the fluid at bubble point, pressure is calculated as

Paraphrasing 3

Paraphrasing 4

  • Where
    Paraphrasing 5 is the bubble temparature formation oil aspect in bbl of bubble point oil / STB,
    Paraphrasing 6 is the bubble point solution gas oil ratio as calculated through the flash liberation in scf/STB.

  • The above steps reoccur at a series of different separator pressures and maintained at a specified temperature [CITATION Tar89 p 394-395 l 3081 ].

Application of Flash Tests

  • Flash test is conducted basically to identify the fluctuations in volumetric behavior of the reservoir liquid and gas that goes through different sections and lastly into the stock.

  • The main agenda of the separator examination is to determine to the lab PVT data which is required for determination of the optimum surface separation conditions which is used to optimize the stock tank oil production [CITATION Tar89 p 394 l 3081 ]

Paraphrasing 7

The above diagram indicates a presentation of schematic regarding the mass increase experiment involving the oil mixture

  • Measured quantity of single phase fluid based on the experimental environment is heated to a specified experimental environment.

  • When pressure rise above the noted reservoir pressure, the fluid tends to stabilize at the single phase condition.

  • Through stabilization, the volume of the sample is noted.

  • Through heating, the noted sample indicates the ability to expand hence spearheads an increase in the volume fluid that contributes towards a reducing pressure.

  • The procedural of determining a PV relationship is achieved through repetitive steps. The procedural requires the pressure to rise beyond reservoir pressure.

  • As for oil mixture, its saturation point is determined at bubble point.

  • Paraphrasing 8based on definition, identifies the volume at the saturation point of the project

  • At every phase of the test, the relative quantity
    Paraphrasing 9 is recorded, inclusive of ratio of actual quantity
    Paraphrasing 10 and saturation pressure quantity
    Paraphrasing 11. Below is its equation

Paraphrasing 12

  • Additionally, where V as the volume of oil, the isothermal compressibility
    Paraphrasing 13 is also listed down above the saturation with a representation of the following equation
    Paraphrasing 14

  • In phase 2, the Y-factor which is a measure of the ration of the relative pressure changes to the total volume is recorded using the below saturation point

Paraphrasing 15

  • The constants mass expansion experiment is basically stopped when the pressure is between the range of 50-100 bar [CITATION Ped14 p 50-52 l 3081 ]

Paraphrasing 16

Paraphrasing 17

Paraphrasing 18

The diagram above indicates the schematic of the constant mass expansion experiment for a gas condensate.

  • The cell is a basic requirement for the condensate cell in a Sloane-type gas for accurate measurements.

  • At a PVT cell, a Known volume of single phase same is charged and heated the required experimental temperature.

  • When the pressure is above the reservoir pressure and saturation pressure the fluid stabilizes.

  • At a pressure of about 50 bar, the A CCE is performed as per earlier description for an oil mixture.

  • The dew point pressure is measured visually and recorded

  • The relative volume is noted down for all pressures

  • When the pressure values are above pressure of saturation, the gas phase compressibility is noted down.

The liquid dropout is analyzed as a percentage of the saturation point volume, at below saturation pressure regarding the calculation below

Paraphrasing 19

  • Regarding the method used in measuring the oil mixture, a similar procedure is used in determining the single phase density of the fluid.

  • By using the measured relative volume data, the measured density is used as the reference, and used for the calculation of compressibility factor and density at other pressure [CITATION Ped14 p 51-53 l 3081 ].

Applications of the constant mass expansion test

  • The main agenda of the constant mass expansion test is to identify the PVT properties of the reservoir fluid

Constant Volume Depletion (CVD)

The schematic of the constant volume depletion (CVD) experiment is shown above.

  • A fixed amount of reservoir fluid (volatile oil and gas condensate) is moved to a cell which is maintained at a reservoir temperature.

  • The cell for the CVD is equipped with a value on the top which allows of depletion of gas while the experiment is being conducted

  • The experiment begins whereby the saturation point volume Vsat and saturation point pressure Psat is recorded.

  • Now, the volume is increased which causes the pressure to decrease, leading to formation of two different phases in the cell

  • The volume of the mixture is gradually reduced to Vsat by allowing excess gas to escape through the top value, while a constant pressure is maintained.

  • The volume of the liquid as a percentage of the saturation point volume and the molar amount of the depleted gas as a percentage of the gas initially present in the cell are made note of

  • The compressibility factor at the cell condition is calculated using the formula
    Paraphrasing 20

  • The molar composition of the depleted gas is also measured.

  • The quantity rises and the excessive quantity is depleted gradually till the pressure is between 100 to 140 bar.

Applications of the test

  • The above test gives us knowledge of the change of PVT properties with respect to time, the PVT properties being that of the produced well streams from the volatile oil reservoirs and gas condensate [CITATION Kar07 p 46-48 t l 3081 ][ CITATION Ste15 l 3081 ]