PVT Experiment Data
In the following sections the different PVT experiments in whitsonPVT are described. The aim of these sections is to describe the functionality of these experiments in the data entry section of the software. For more information about the methods and guidlines for the PVT experiments, see the methods section or the wiki.
Depletion Experiments
The depletion experiments are the most common PVT experiments, and emulate various parts of the fluid phase behavior throughout the production process. The different depletion experiments alter system variables, pressure, temperature and composition. To develop an accurate fluid model, all three variables should be spanned to avoid poor model extrapolation. Table 1 shows what system variables are changed for the different depletion experiments.
Table 1: Overview of PVT experiments and what variables are changed for each experiment.
| Experiment | Pressure | Temperature | Composition |
|---|---|---|---|
| CCE | x | ||
| DLE | x | x | |
| MSS | x | x | x |
| CVD | x | x |
Constant Composition Expansion (CCE)
The constant composition expansion (CCE) experiment is probably the most common PVT experiment, and it aims to describe the phase behavior of the undersaturated depletion stage during production. The main outputs of the CCE experiment are (1) volumetric behavior for depleting pressure (particularly for the undersaturated region), and (2) an estimate of the saturation pressure. The CCE experiments does not vary the temperature or the fluid composition.
Differential Liberation Expansion (DLE)
The differential liberation expansion (DLE) experiment is a common experiment which was developed to emulate depletion of a black-oil fluid system. The DLE experiment spannes pressure and composition ranges, but is kept at a contant temperature.
Note
Write about what solution GOR and liberated gas is and what the differences are!
There are three datasets for a DLE experiment in whitsonPVT. The first dataset is the stage data which are the saturated properties of the system at each pressure stage. The second dataset is the liberated gas compositions. This table is automatically generated based on the number of stages in the stage data section (the first dataset). We recommend inputting the mole compositions of the liberated gas at each stage, as this data can be useful in the fluid model development and the data quality check throughout the material balance checks. The last dataset is the residual oil composition, which is also useful for the fluid model development and data quality checks. We recommend inputting the mass composition here if the lab reports it.
In whitsonPVT the component slates do not need to be the same for our solutions to work! All the work of splitting and lumping will be handled automatically to make the data entry more convenient and consistent.
In some special cases, the last pressure stage goes directly to standard conditions, without having a last DLE stage at the experiment temperature. In this case, there will be some gas removed when reducing both pressure and temperature. This is handled by allowing for an additional input of the specific gravity in the residual fluids information at standard conditions box.
Multi-Stage Separator (MSS)
The multi-stage separator (MSS) experiment is a less common, but really important PVT experiment. The MSS experiment was developed to emulate the separator process. It is the only depletion experiment that varies all three system variables (pressure, temperature, and composition). The MSS is similar to the DLE experiment, but it differs in that the number of stages is less (three or four) and that the temperature varies for each stage.
Constant Volume Depletion (CVD)
The constant volume depletion (CVD) experiment is a common depletion experiment for gas condensates and volatile oil fluids. The whitsonPVT data structure is the same as for the DLE experiment. One difference is that the residual fluid condition is typically not at standard conditions.