Oil and fossil fuel were shaped from the remains of prehistoric plants and animals. That is the only reason we do refer them as fossil fuels. Long time ago, the prehistoric plants and animal remains both were settled into the seas beside the sand silt and the rocks. As the rocks and silt both were settled down layer by layer amassed in rivers on coastlines and on the bottom layer of the ocean manufacturing the organic material.
With the passage of time, increasing pressure and temperature modifies the mud sand and silt into rock and slowly cooks the organic matter into fossil fuels. Fossil fuel is controlled within the rock forming exactly the same way a sponge is holding the water.
The oil explorers hunted for oil seeps at the surface sure forms of rock outcrops and different surface signs that oil may exist below ground. this was a haphazard methodology. However, science and technology,in no time, was developed to boost the industries ability to see what lies under the earths surface.
Moreover,the geologists studied rocks on the earths surface and underground. They created a map of the rocks wherever they thought oil and gas might be found. Engineers use this natural science map to drill a well below the earths surface.