While several theories exist to explain the development of natural gas, the most widely accepted holds that natural gas and crude oil are the result of the decomposition of plants and animals buried deep beneath the surface of the earth. The theory goes something like this. Organic material typically oxidizes as it decomposes. Some organic material, however, was either buried before it decomposed or deposited in oxygen-free water, thereby preventing the oxidation process. Over millions of years, sand, mud and other sediments – along with these decomposed plants and animals – were compacted into rock. As layer upon layer of material covered this rock, the weight of the earth above along with the earth’s heat changed the organic material into oil and gas. Over thousands of years the earth’s pressure pushed these substances upward through permeable material until they reached a layer of impermeable rock where they became trapped. Natural gas accumulates in reservoirs that are typically found between 3,000 and 25,000 feet below the earth’s surface. Gas may be found in “conventional” or “unconventional” formations as shown in the illustration below.
