Kerogen type and maturity
Exploring for Oil and Gas Traps | |
Series | Treatise in Petroleum Geology |
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Part | Critical elements of the petroleum system |
Chapter | Evaluating source rocks |
Author | Carol A. Law |
Link | Web page |
Store | AAPG Store |
Each kerogen type has its own relationship to maturity parameters. Maturity measurements are made on materials other than kerogen; therefore, they are not a direct measure of the hydrocarbon generation stage of the source intervals. A relationship must be established between maturity of the geologic section and hydrocarbon generation for each kerogen type in a basin. This relationship can be derived using 1-D basin modeling techniques.
Hydrocarbon generation and maturity
The hydrocarbon generation-depth curve in Figure 1 indicates where various phases of hydrocarbons would be generated today in the geologic section if a uniform kerogen existed throughout. We would use the following steps to compare the relationships.
Step | Action |
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1 | Define the hydrocarbon generation stage for a calibrated well based on the depth vs. hydrocarbon yield plot (left figure). For example, the onset of oil generation occurs at approximately length::2.1 km. Then transfer to the depth versus maturity plot (in this case vitrinite reflectance, right figure) and follow across at length::2.1 km until you reach the maturity profile. This vitrinite reflectance value (0.55 %Ro ) would indicate the onset of hydrocarbon generation in this well. |
2 | Apply this relationship to predict the generation zones for this specific kerogen in wells with similar thermal and burial histories in the basin for which maturity data are available. |
Comparison and maturity measures
The table below shows examples of the relationships between hydrocarbon generation zones, maturity, and transformation ratio for standard types II and III kerogens, based on a specific burial and thermal history model. The most significant difference is in the depth to the onset of oil generation, where depth::1000 m separates the top of the oil windows of these two kerogen types.
Hydrocarbon generation zone | Vitrinite refl., % Ro, Type II | Vitrinite refl., % Ro, Type III | Transformation ratio, %, Type II | Transformation ratio, %, Type III | Present-day depth, m, Type II | Present-day depth, m, Type III |
---|---|---|---|---|---|---|
Onset oil | 0.55 | 0.85 | 5 | 12 | 2200 | 3200 |
Onset peak rate generation | 0.65 | 1.00 | 17 | 31 | 2600 | 3500 |
Onset gas/cracking liquids | 0.95 | 1.35 | 88 | 64 | 3400 | 4050 |
See also
- Relationships between maturity and hydrocarbon generation
- Kerogen type and hydrocarbon generation
- Kerogen type and transformation ratio
- Kerogen types: comparison of maturity measures
- Open- vs closed-system generation modeling