Page 90 - PVT Property Correlations

68 PVT Property Correlations

While
1; 000; 000
R 5 ð4:2Þ
CGR
Specific gravity of oil is related to API gravity by Eq. 4.3, and the molec-
ular weight of stock-tank oil can be calculated from Eqs. 4.4 or 4.5.

141:5
γ 5 ð4:3Þ
o
API 1 131:5
5954
M o 5 ð4:4Þ
API 2 8:811
or
42:43γ
M o 5 o ð4:5Þ
1:008 2 γ o

Option 4—Two-Stage Separation With Full Definition

Wet gases are usually processed with either two (one separator and stock-
tank) or three (two separators and stock-tank) stage separation system. If
two-stage separation is utilized, we can use Eq. 4.6 to estimate the reservoir
gas specific gravity. The equation requires knowledge of both the separator
GOR and the stock-tank GOR (which is usually not available). It requires
also that the specific gravity of both the first stage separator gas and the
stock-tank gas be known. Practically, the stock-tank gas specific gravity is
seldom available. Other quantities in the equation such as specific gravity of
stock-tank condensate can be evaluated from the API gravity and molecular
weight of stock-tank condensate can be estimated from the correlations
above.
R 1 γ 1 4602γ 1 R 3 γ
γ 5 1 o 3
gw ð4:6Þ
R 1 1 133; 310γ =M o 1 R 3
o
Option 5—Three-Stage Separation With Full Definition

As with the option above, for the three-stage separation system (two separa-
tors and stock-tank), the specific gravity of the reservoir gas can be calcu-
lated from the following equation. GORs and specific gravity of separators
and stock-tank gases must be known.
R 1 γ 1 4602γ 1 R 2 γ 1 R 3 γ
γ gw 5 1 o 2 3 ð4:7Þ
R 1 1 133; 310γ =M o 1 R 2 1 R 3
o