Selecting a surficial geochemistry survey method
| Exploring for Oil and Gas Traps | |
| |
| 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 |
How does one select a method(s) for a surface geochemical exploration program? The choice of method(s) depends on the kinds of questions you hope the survey results will answer.
- What are the objectives of the survey—to demonstrate the presence of an active petroleum system in a frontier area, to high-grade previously defined exploration leads and prospects, or to determine the type of petroleum (i.e., oil vs. gas) likely to be encountered?
- What other data are presently available for the area of interest (satellite imagery, aeromagnetics, gravity, seismic, etc.)?
- What geochemical methods have previously been used successfully in the area of interest or in a geologic analog area?
- What limitations are imposed by the survey area (onshore or offshore, deep water or shallow, jungle or desert, mature basin or remote area, budget and personnel constraints)?
Direct vs. indirect methods[edit]
As a generalization, direct hydrocarbon methods are preferred over indirect methods (see Surficial geochemistry and hydrocarbon detection methods) because they can provide evidence of the very hydrocarbons we hope to find in our traps and reservoirs. Additionally, chemical and isotopic analysis of these hydrocarbons, especially the high-molecular-weight hydrocarbons, can provide insight into the nature and maturity of the source rock that generated these hydrocarbons.
Offshore methods[edit]
The table below lists the principal geochemical methods used for offshore exploration.
| Medium to be Sampled | Target to be Analyzed | Methods |
|---|---|---|
| Atmosphere | Hydrocarbons | Radar or laser |
| Water surface | Oil slicks or sheens | Satellite, airborne sensors (radar, multispectral imaging, hyperspectral imaging, laser, fluorescence), or direct sampling |
| Water | Dissolved hydrocarbons (low molecular weight (LMW), high molecular weight (HMW), or aromatics) | Marine sniffer, water analysis |
| Sea bottom | Hydrocarbon macro- or microseepage | High-resolution seismic data, side-scan sonar, direct sampling (gravity core, vibracore, piston core, jet core, etc.) |
| Hydrocarbon-induced alteration | Topographic, acoustic, and temperature contrasts; sediment sampling for microbial or geochemical indicators |
Onshore methods[edit]
The table below lists the principal geochemical methods used for onshore exploration.
| Medium to be Sampled | Target to be Analyzed | Methods |
|---|---|---|
| Land surface | Oil and gas macroseeps, stains, impregnations | Geologic mapping; historical records; satellite and airborne sensors (multispectral, hyperspectral); direct sampling of seeps, stains |
| Hydrocarbon microseeps | Soil or sediment sampling for hydrocarbon analysis | |
| Hydrocarbon-induced alteration | Soil or sediment sampling for indirect microbial or geochemical indicators, aeromagnetic, electrical, or radiometric | |
| Soil air | Light hydrocarbons | Probe or adsorptive collectors |
| Nonhydrocarbons | Probe or adsorptive collectors | |
| Soil or sediment | Light hydrocarbons, aromatics | Sample disaggregation and/or acid extraction for chromatography, UV-fluorescence |
| Nonhydrocarbons or diagenetic anomalies | Hydrocarbon-oxidizing microbes, soil salts (i.e., carbonates, chloride, iodine, sulfate, etc.); clay minerals; trace metals; magnetic susceptibility, aeromagnetics, ground magnetics; electrical (induced polarization [IP], controlled source audio magnetotellurics [CSAMT], resistivity, magnetotellurics [MT]); radiometrics |
Recommendations[edit]
Whenever possible, use more than one geochemical survey method, for example, combine a direct method with an indirect method. The use of multiple methods can reduce interpretation uncertainty because seepage-related anomalies tend to be reinforced while random highs and lows tend to cancel each other. If surface conditions or budgetary constraints preclude the use of direct hydrocarbon detection methods, the next best choice is the indirect method most closely linked to hydrocarbons and hydrocarbon accumulations (microbial, helium, and perhaps certain magnetic and radiometric methods).
See also[edit]
- Surficial geochemistry and hydrocarbon detection methods
- Surficial geochemical survey objectives
- Designing a surficial geochemical survey
- Surficial geochemical interpretation guidelines
External links[edit]
| find literature about Selecting a surficial geochemistry survey method |
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