CCE and CVD results

1
CCE and CVD results

• The usual PVT measurements on gas condensates are
  
• Constant Composition Expansion (CCE) sometimes
  called Constant Mass Expansion
• Constant Volume Depletion (CVD)
• A CCE test is used to measure the dew point
  pressure, and to provide volumetric data above
  and below the dew point pressure.
• A CVD test measures data below dew point
  pressure.
• Below dew point pressure, a CVD test is much more
  valuable than CCE as it provides data on the
  equilibrium gas composition.

2
Constant Composition (Mass) Expansion Test

• Data
• Dew point pressure
• Z-factor
• Total volume (rel. to volume at dew point)
• Liquid phase volumes

3
CCE results
4
Constant Volume Depletion Test
P3 lt P2
P1 Pdew
P2 lt Pdew

• Data
• Amount of gas removed (in moles)
• Equilibrium gas Z-factor
• Equilibrium gas composition and C7 properties
• Liquid saturation

5
CVD results
6
Calculated recoveries from CVD results
7
Using CVD results

• The CVD test simulates closely the actual
  behavior of a gas condensate reservoir undergoing
  pressure depletion, and results from the lab
  measurements can be used directly to quantify
  recoveries of surface gas and condensate as a
  function of pressure below the dewpoint.
• Combined with single-phase Z-factors from the CCE
  test, a complete prediction of depletion behavior
  (recoveries and liquid-yield variation) can be
  accurately predicted from initial pressure to
  abandonment.
• Accurate measurement of the removed gas
  composition is very important to the prediction
  of condensate recovery and liquid-yield variation
  much more important than accurate measurement
  of retrograde oil volumes.
• Special laboratory procedures should be followed
  to ensure accurate CVD compositional measurements
  (e.g. appropriate heating of tubing used to
  remove equilibrium gas from the cell).

8
Material Balance Checks of CVD results

• Measurement of the final low-pressure condensate
  composition allows an important material balance
  check of CVD results.
• The best technique is a backward
  material-balance.
• This starts with the final condensate composition
  and amount (using the reported final oil relative
  volume and properties), adding incrementally the
  removed gas from each CVD step, and ending up
  with a check of the original fluid composition.
• Material balance can also be used to calculate
  the liquid phase composition and density at each
  CVD step. Densities and K-values can then be
  compared with results of correlations.