中文：

天然气是一种主要由甲烷组成的烃类气体混合物，通常与石油在同一地层中同时形成。它是一种清洁、高效的能源，被广泛用于民用和工业领域。

天然气的组成成分中，甲烷的含量最高，通常占80%以上。此外，还含有少量的乙烷、丙烷、丁烷等烃类气体，以及氮气、二氧化碳等非烃类气体。不同地区、不同气田的天然气组成成分有所不同，因此其热值、密度等参数也会有所不同。

天然气主要由古生物在地下经过长时间的高温和高压作用形成的。在古生代，大量植物和动物死亡后沉积在湖泊或海洋中，并逐渐被泥沙掩埋。随着时间的推移，这些有机物质逐渐被细菌分解，产生甲烷等气体，并逐渐积累在地下深处。当这些气体达到一定压力时，它们会通过地层裂缝向上渗透，最终聚集在一起形成天然气田。

英文：

Natural gas is a mixture of hydrocarbon gases mainly composed of methane, usually formed simultaneously with oil in the same strata. It is a clean and efficient energy source, widely used in civil and industrial fields.

Among the natural gas components, methane usually accounts for more than 80%, and is accompanied by small amounts of ethane, propane, butane and other hydrocarbon gases, as well as nitrogen, carbon dioxide and other non-hydrocarbon gases. The composition varies in different regions and different gas fields, so its parameters such as calorific value and density may also vary.

Natural gas is mainly formed by ancient organisms after long-term high temperature and high pressure underground. In the Paleozoic era, a large number of plants and animals died after sedimentation in lakes or oceans and were gradually buried by silt. With the passage of time, these organic substances were gradually decomposed by bacteria to produce gases such as methane, which gradually accumulated in the deep underground. When these gases reach a certain pressure, they will penetrate upward through the strata to form natural gas fields.