Surface geochemical techniques to detect these changes in chemistry have been used with success since the 1930's. First developed by the Russians as a way to compete with the larger budgets of the American oil industry. Their low cost taken together with their significant increase in drilling accuracy yield, make them a powerful tool for petroleum exploration.
Iodine Sampling
Iodine's proposed surface relationship to petroleum accumulations at depth begins with the hydrocarbon gases reaching the soil/air interface. Under infrared and ultraviolet light, the hydrocarbons react, the with the iodine and form iodorganic compounds present.
Trace Elements
Trace and major elements, certain isotopes, and the compounds in which they are incorporated have been used to identify petroleum microseepage.
Soil Gas
Measuring vapor or liquid hydrocarbons occuring in the soil, atmosphere, ocean water column, ocean bottom sediments, and groundwater or surface fresh water is the most common method for detecting and delineating a surface anomaly.
Magnetic Susceptibility
The magnetic susceptibility of soil minerals is discussed, and in particular that of the ferrimagnetic minerals, maghemite, magnetite, and the titanomagnetites since one or more of these usually dominates soil magnetic properties. The magnetic susceptibility of soil depends on the shape, size, and concentration of these minerals as well as on the method of measurement. Measurements performed in a weak alternating magnetic field are the most reliable.
The identification, formation, and occurrence of soil maghemite is considered in detail since it is usually of pedogenic origin and occurs in (magnetically) detectable amounts in most soils. Moderate concentrations (>1 per cent) of magnetite or titanomagnetite in soils may be accurately measured if some of the material is first magnetically separated and its susceptibility determined. An example is given of the use of susceptibility measurements. Pedogenic maghemite may be determined in soils developed from parent materials of low susceptibility. A very rough value of 8.8 × 10−4 m3 kg−1 is suggested for the mass susceptibility of such maghemite (excluding magnetic concretions).
Although susceptibility has been suggested as an indicator of soil forming processes, this is only possible within an area containing fairly uniform parent material.