Oil wells are expensive to drill and there is no guarantee that they will hit oil. In order to increase the chances of finding oil, geologist need to know as much as possible about the geology of an area. Geologist look for areas where the characteristics described in the previous section occur, favorable source rocks, reservoir rocks and traps.
The first thing a geologist would do when exploring for oil and gas in a new area is map the surface geology. Remote sensing, such as satellite images is useful in understanding the regional geology of a large area, especially in remote parts of the world. This image of the Appalachian Mountains near Harrisburg PA shows the Valley and Ridge Province, an area of folded and thrust faulted sedimentary rocks.
For a closer look, geologist may rely on aerial photographs. Due to differential erosion sandstones occur as ridges and shales as valleys. This photo of Little Dome WY shows a doubly plunging anticline.
Geologist often use topographic maps as base maps, because, they are very accurate, readily available, and much of the geology can be interpreted from the topography.
Although, remote sensing techniques such as satellite photos and aerial photography yield a significant amount of information, to get a true picture of the geology one must conduct field studies. Field studies consist of identifying the rock type, measuring strike and dip of beds, and measuring the thickness of formations. Samples may be collected for petrographic, geochemical or paleontological studies back at the lab.