Natural gas is a fossil fuel created by thousands of years of strong heat and pressure on layers of buried plants, gases, and animals. Natural gas stores the energy that plants initially acquired from the sun in the form of chemical bonds. Because it cannot be replaced on a human time scale, natural gas is a non-renewable resource. Natural gas is a hydrocarbon gas mixture that mostly consists of methane, but also contains various proportions of other higher alkanes, as well as a small quantity of carbon dioxide, nitrogen, and/or hydrogen sulfide. Natural gas is a common energy source for heating, cooking, and generating electricity. Petroleum refers to both gases and liquid crude oil that are made up of fluid hydrocarbons. Petroleum is nearly exclusively found in sedimentary rocks, as is well known (sandstones, limestones, and claystone). Igneous and metamorphic rocks rarely contain petroleum. As a result, sedimentary rocks play a significant role in petroleum geology. It examines current processes on the earth's surface in order to learn how organic debris can be buried and stored in fine-grained sediments. It addresses where and how porous sands are deposited, as these could later function as petroleum storage reservoirs. It's also crucial to understand the distribution of porosity and permeability in sedimentary rocks.