Information from remote sensing and field studies are compiled onto a geologic map. This map of Calgary Alberta shows anticlines and thrust faults which are potential hydrocarbon traps.
On the generalized geologic map of Ohio the different colors represent rocks of different geologic age. The surface geology can be used to interpret the subsurface geology.
Seismic surveys are used to determine the structure of rocks in the subsurface. A vibrator truck or small explosion is used to generate seismic waves. Sedimentary layers reflect the seismic waves which are recorded on geophones. The travel times are recorded and used to interpret the rock structure.
This is an actual seismogram that has been processed by a computer to enhance the geologic structures. Structural traps occur below the A and B.
Detailed records are kept whenever a well is drilled. This way, even if a well is a dry hole, geologist still get significant data that can be used to determine where to drill the next well. After a well is drilled geophysical tools, that measure properties such as resistivity or gamma rays, are dropped down the bore hole and slowly brought to the surface, resulting in a bore hole log. By compiling data on the production history of a field and studying the available geophysical logs the petroleum geologist can get a three dimensional view of the subsurface geology.
Sometimes samples of rock are collected as the well is drilled. These samples are used for detailed petrographic studies such as determining the reservoir rocks porosity and permeability.
The final tool in the petroleum geologist bag is geochemistry. Geochemical analyses are often done to determine if there is a potential source rock present.