Gas condensate properties
Gas condensates are liquids, generally straight chain alkanes in the C2 to C6+ range, that can condense from gas when the temperature and pressure drop sufficiently low.
Condensate versus distillate
The terms "condensate" and "distillate" are used interchangeably to describe the liquid produced in tanks, but each term stands for a different material.  Along with large volumes of gas, some wells produce a water-white or light straw-colored liquid that resembles gasoline or kerosene. The liquid has been called "distillate" because it looks like products obtained in refineries by distilling the volatile components from crude oil. But it has also been called "condensate" because it is condensed out of the gas produced by the well.
Lease condensate, called so because it is produced at the leas level from oil or gas wells, is the most commonly discussed type of gas condensate. This condensate is generally recovered at atmospheric temperatures and pressures from wellhead gas production and can be produced along with large volumes of natural gas.
The API gravity of lease condensate ranges between 45 and 75 degrees, and lease condensates with higher APIs contain more NGIs, which include ethane, propane and butane, but not many heavy hydrocarbons. Higher API lease condensate is also clear or translucent. On the other hand, lease condensates with a lower API gravity are a black or near black color, like crude oil, have higher concentrations of heavier compounds.
Importance of measuring condensates
When a hydrocarbon reservoir is found, knowing the types of fluids that are present, along with their main physicochemical characteristics, is important. Generally, that information is obtained by performing a PVT analysis on a fluid sample of the reservoir. Normally, a PVT analysis can take several months, which limits the number and type of reservoir studies that can be conducted.
Conventional production measurements, such as a DST (drill stem test) are the only parameters that can be measured almost immediately after a well is completed. Obtaining preliminary values of properties such as: molar percentage of heptane and heavier components (% mole of C7+), molecular weight of the original fluid (MW), maximum retrograde condensation (MRC) and dew point pressure (Pd). Most of these properties are very important for exploitation of gas condensate reservoir and their early early availability will allow engineers to carry out reservoir studies that will ensure an efficient exploitation and maximize the final recovery of the liquids present in the reservoir.
The only parameter needed to use these correlations is the value of the gas condensate ratio (GCR) of the fluid during the early stage of production. These empirical equations should be valid for any gas condensate reservoir worldwide; although a range of usability is proposed for a better performance of the correlations.
- Thornton, O.F. 1946. Gas-Condensate Reservoirs-A Review. Presented at API Drilling and Production Practice, New York, 1 January. API-46-150. https://www.onepetro.org/conference-paper/API-46-150.
- Braziel, R. 2012. Fifty Shades of Condensates--Which One Did You Mean? Oil & Gas Financial Journal. October 23, 2012. http://www.ogfj.com/articles/2012/10/fifty-shades.html.
- Paredes, J.E., Perez, R., Perez, L.P., and Larez, C.J. Correlations to Estimate Key Gas Condensate Properties through Field Measurement of Gas Condensate Ratio. 2014. Presented at the SPE Annual Technical Conference and Exhibition, Amsterdam, 27-29 October. 170601-MS. SPE-170601-MS-
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