Difference between revisions of "Selecting a surficial geochemistry survey method"

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* 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 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 ([[Remote sensing|satellite imagery]], [[Magnetics#Aeromagnetic_surveys|aeromagnetics]], [[Gravity basics|gravity]], [[Seismic data|seismic]], etc.)?
+
* What other data are presently available for the area of interest ([[Remote sensing|satellite imagery]], [[Magnetics#Aeromagnetic_surveys|aeromagnetics]], [[gravity]], [[Seismic data|seismic]], etc.)?
 
* What geochemical methods have previously been used successfully in the area of interest or in a geologic analog area?
 
* 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)?
 
* 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)?

Revision as of 19:48, 22 February 2016

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]

External links[edit]

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