Surface sampling of reservoir fluids is taken from individual gas and liquid streams from a production separator or similar installation. Other than methods used for new offshore wells, it is by far the most common method of sampling pressurized hydrocarbon fluids.
Samples of gas and liquid exiting the separator are acquired, along with separate flow rate measurements of each, providing the gas-oil ratio (GOR). The fluids are then recombined in the laboratory to recreate representative reservoir fluids for accurate analysis. Refer to PVT Laboratory Testing – Best Practices.
Applications
PVT analysis is the scientific process used to determine phase behavior and fluid properties of oil and gas samples from your well—both in the reservoir (downhole) and at the surface. This analytic testing information gives you a better understanding of your hydrocarbon reserves, so you can apply the most cost-effective extraction methods to optimize production. Refer to PVT Lab Testing – Best Practices.
Data in Context
GeoMark maintains a database of thousands of onshore, separator fluid PVT reports (www.rfdbase.com) for easy reference. This data provides excellent context when considering the behavior of new fluids. For example, unconventional fluids often have PVT properties that track well with thermal maturity.
FAQ
Q. Are the separator gas and oil samples reliable?
A. This question is answered by the opening pressures and initial flash validations. Opening pressures should correspond to the reported pressures from the field. The flash validations should show consistency between duplicate samples.
Q. What is the correct recombination GOR?
A. This is often the most difficult, but key question, in conducting recombined PVT studies. Ideally, the GOR should be stable for an extended period. Also, geochemical analyses are often used to confirm, or question, the validity of the planned GOR for a PVT study.
Q. Why is the bubble point pressure so critical in unconventional oil wells?
A. Dropping below the bubble point pressure dramatically reduces oil production in unconventional wells. PVT studies are used to determine this pressure and identify any corresponding gap to the reservoir pressure.
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