Recent Developments in Understanding Gas Behaviour in SAGD Projects

1
Recent Developments in Understanding Gas
Behaviour in SAGD Projects
Thimm Engineering Presents

• Dr. Harald F. Thimm
• Thimm Engineering Inc.

2
Henrys Law and Solubility

• Henrys Law governs the solubility of gases in
  solvents
• Solubility is inversely proportional to Henrys
  Constant (KH)
• Absolute solubility (y 1) of a gas 1/K, where
  K is the equilibrium constant
• Solubility of gases in water is normally reduced
  when temperature rises
• However
• As critical point is approached, solubility
  increases sharply

3
Henrys Law (cont.)

• This increased solubility in water at high
  temperature is followed by
• CH4, C2H6, N2, O2, CO2, noble gases1
• H2S2
• Asymptotic behaviour near critical point governs
  at 180C or even lower in some cases
• This behaviour is important at SAGD conditions
• 1. Harvey Levelt Sengers2. Suleimenov Krupp

4
Henrys Law Constant for Methane in Water
Henrys Law Constant for CH
in H
O
4
2
11.5
11.0
Point of minimum solubility
10.5
At high temperature, solubility increases
dramatically
10.0
/ 1 bar)
H
ln(K
9.5
9.0
8.5
8.0
250
300
350
400
450
500
550
600
650
Temperature (K)
5
K-Values The Solubility of Selected Gases in
Water
K-Values for Selected Gases in Water at
Saturated Steam Temperatures
120000
100000
80000
nitrogen
CO2
K-Value
60000
methane
oxygen
40000
20000
0
160
175
190
205
220
235
250
265
310
100
115
130
145
280
295
Temperature in Degrees C
6
Gases in Petroleum Production by SAGD

• Methane
• Carbon Dioxide
• Hydrogen Sulphide
• Nitrogen (lt2)
• Hydrogen (lt2)
• All become significantly soluble in water (steam
  condensate) in the 180C - 240C steam
  temperature range

7
SAGD Steam Chamber
Ceiling drainage
Slope drainage
Horizontal production well
Horizontal injection well

• Drainage to the production well is essentially
  only bitumen water. Gas production is
  therefore via dissolution in produced fluids
• Henrys Law can be used to predict this gas
  production

8
Typical Results Field vs. Predicted

• Normally GOR 1 8
• H2S varies from 1,000 to 30,000 ppm
• Predictions match field results

9
Flexibility of Predictive Method

• In many cases, gas is injected or steam pressure
  is varied during the life of a SAGD well pair
• Both have the effect of altering the methane to
  carbon dioxide ratio in produced gases
• This method is robust enough to predict the
  effects of these changes on produced gas
  composition, as shown on the following slide

10
Field vs. Theoretical Results
Produced Gas Carbon Dioxide Content
Carbon Dioxide
0
1
2
3
4
5
6
Production Phase

• Field Measurements

Calculated by this theory
11
Applications of Method

• Re-pressurisation of gas caps with another gas
• Greenhouse gas predictions
• Facilities prediction of gas partitioning
• Prediction of hydrogen sulphide - sulphur
  recovery needs for commercial plants
• Carbon dioxide and flue gas injection
• Oxygen breakthrough in firefloods phenomenon is
  a possible contributor?
• Other (corrosion, scaling, etc. - dependent on
  CO2)