Above is a photograph through a microscope of actual sandstone, which is a porous rock.  The photograph shows the pores between the grains.  It is in these pores that the gas migrates or collects.

Previous - Slide 6 - Next

We now know that gas does not flow in rivers underground.  Over eons, gas occurs in, or migrates upwards through, porous and permeable rocks until it hits a layer of “cap rock” that is not porous or permeable.  The gas is “trapped” beneath that cap rock in a pool from which it can be produced.

(At that time natural gas was not considered valuable, and was released or lighted and flared into the atmosphere so that the oil could be produced.  Now, gas is the predominant hydrocarbon for which wells are drilled in West Virginia.  For the most part, the remainder of this slide show will usually talk about gas wells, but the principles apply to both.)