Surficial geochemical case history 3: Predrill–postdrill comparison
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It has been suggested that this article be merged with [[::Surficial geochemical case histories|Surficial geochemical case histories]]. (Discuss) |
| Exploring for Oil and Gas Traps | |
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| Series | Treatise in Petroleum Geology |
|---|---|
| Part | Predicting the occurrence of oil and gas traps |
| Chapter | Surface geochemical exploration for petroleum |
| Author | Dietmar Schumacher |
| Link | Web page |
| Store | AAPG Store |
The significance of surface geochemical anomalies in hydrocarbon exploration are often difficult to quantify. Potter et al.[1] summarize one company's experience with a soil gas geochemical method. Their exploration program involved geochemical surveys of 139 prospects located in both mature basins and frontier basins, onshore and offshore, in a wide variety of environments. Targets ranged in depth from 1,000–15,000 ft (300–4,4600 m) and covered the full spectrum of trap styles; survey areas ranged from as small as a few hundred acres to regional programs covering 1,000 mi2 (2,590 km2).
Results
The 139 surveys led to the drilling of 141 wells in previously undrilled prospects. A total of 43 wells were drilled in negative geochemical anomalies, and 41 of these encountered no hydrocarbons. Of the 98 wells drilled in positive geochemical anomalies, 92% encountered reservoired hydrocarbons and 76% were completed as producers. This company's experience is fairly typical and documents that integration of seismic data and geochemical data yields greater definition of exploration targets than provided by either method separately.
Conclusion
Although the discovery of a surface geochemical anomaly does not guarantee the discovery of commercially significant hydrocarbons, it does establish the presence of hydrocarbons in the area of exploration interest. Seeps and microseeps at the surface represent the end of a petroleum migration pathway. Traps and structures along such migration pathways should be considered significantly more prospective than those not associated with hydrocarbon anomalies.
Surface geochemical exploration methods cannot replace conventional exploration methods, but they can be a powerful complement to them. Geochemical and other surface methods have found their greatest utility when used in conjunction with available geological and geophysical information. The need for such an integrated approach cannot be overemphasized. Properly applied, the combination of surface and subsurface methods will lead to better prospect evaluation and risk assessment.
See also
- Surficial geochemical case histories
- Surficial geochemical case history 1: structural traps
- Surficial geochemical case history 2: stratigraphic trap
- Seepage activity and surficial geochemistry
References
- ↑ Potter, R., W., IIHarrington, P., A., Silliman, A., H., Viellenave, J., H., 1996, Significance of geochemical anomalies in hydrocarbon exploration: one company's experience, in Schumacher, D., Abrams, M. A., eds., Hydrocarbon Migration and Its Near-Surface Expression: AAPG Memoir 66, p. 431–439.
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