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Separator shrinkage

\label{sep_shrinkage}

The separator production data and daily wellstream compositions are used to calculate daily

  • Separator Oil Shrinkage Factors
  • Separator Oil Flash Factor
  • Total Producing GOR

Separator Oil Shrinkage Factor

Separator-oil shrinkage factor, or just shrinkage factor (SF), is the fraction of metered separator oil rate that remains (transforms into) stock-tank oil after further processing down to standard conditions of 1 atm and 60 °F (Hoda & Whitson 2013). In layman's terms, the shrinkage factor quantifies the decrease in oil volume from separator conditions to stock tank, and the magnitude can range from <0.65 - 0.99.

Flash Factor

Separator-oil flash factor, or just flash factor (FF), is the ratio of liberated gas from metered separator oil after further processing down to standard conditions of 1 atm and 60 °F. In layman’s terms, the flash factor accounts for the increase in gas volume from separator conditions to stock tank. It is the exact reason why oil is shrinking, i.e. gas is coming out of solution. The magnitude of the flash factor can range from 5 scf/STB–1000 scf/STB (and even more).

Total GOR

Total producing GOR, \(R_p\), can be calculated easily when knowing shrinkage factor and flash factor: \(R_p = R_{p,sep}/SF + FF\). A shrinkage factor is always associated with a flash factor and is literally the solution GOR of the separator oil (\(R_{s,sep}\)).

Requirements to Estimate Wellstream Compositions:

  • A properly tuned EOS model
  • An estimate of a wellstream comp – “seed feed”
  • Separator volumetric rates (GOR)
  • Separator conditions (Tsep, psep)

Requirements to Calculate Shrinkage Factor and Flash Factor Daily:

  • Consistent fluid description
  • Fundamental physical and thermodynamic principles

Want to know more? Here is a presentation on separator oil shrinkage and flash factors.