Nontechnical Guide to Petroleum Geology, Exploration, Drilling and Production / Нетехническое руководство по нефтяной геологии, разведке, бурению и добыче

Both crude oil and natural gas occur naturally in subsurface deposits. Crude oil is a black liquid that is sold to refineries to be refined into products such as gasoline and lubricating oil. Natural gas is a colorless, odorless gas that is sold to gas pipelines to be transported and burned for its heat content. There are many different types of crude oils and natural gases, some more valuable than others. Heavy crude oils are very thick and viscous and are difficult or impossible to produce. Light crude oils are very fluid, relatively easy to produce, rich in gasoline, and more valuable. Some natural gases burn with more heat than others and are more valuable. Some natural gases also contain almost pure liquid gasoline called condensate that separates from the gas when it is produced. Condensate is almost as valuable as crude oil. Sulfur is a bad impurity in both natural gas and crude oil. Sour crude oils contain sulfur, and sour natural gases contain hydrogen sulfide and are less valuable. Crude oil is measured by volume in barrels (bbl). Natural gas is measured by volume in thousands of cubic feet (Mcf) and by heat content in British thermal units (Btu). <...>