天然气成因类型及其鉴别

中国经过20年天然气科技攻关，已形成天然气成因类型及其鉴别标志的理论体系和方法。天然气成因类型可划分为有机成因气、无机成因气、混合成因气3大类。有机成因气根据演化程度划分为生物气、生物一热催化过渡带气、热解气和裂解气，根据母质类型划分为煤成气（包括煤成热解气和煤成裂解气，在天然气资源中占主导地位）和油型气（主要是原油伴生气，包括油型热解气和油型裂解气）；无机成因气以二氧化碳为主，分为岩石化学成因和幔源成因两种主要类型；混合成因气是两种或两种以上成因类型气混合而成的天然气，常见的主要有3类（同一烃源岩不同热演化阶段生成天然气的混合，不同烃源岩生成天然气的混合，有机成因气和无机成因气的混合）。常用的天然气成因类型鉴别指标有天然气组分、烷烃气碳同位素、二氧化碳碳同位素和轻烃参数，其中，碳同位素是判别各类成因天然气最有效和最实用的指标。图1表2参41

Origin and identification of natural gases

In the past 20 years, many researchers were engaged in tackling the key problems about natural gases, and brought about the theory and methods on origins and identification marks of natural gases. The natural gases include organic gases, inorganic gases and hybrid gases according to their origins. Gases of organic origin can be subdivided into biogenic, biogenicthermal catalyzed, pyrogenic, and cracked gases, and can also be subdivided into coal derived gases and petroliferous gases according to the types of parent material. Coal derived gases include coal derived pyrogenic gases and coal derived cracked gases, which play a dominant role in natural gas resources. Petroliferous gases mainly refer to the associated gas of crude oil, including petroliferous pyrogenic gases and petroliferous cracked gases. Inorganic gases give priority to CO2 , including petrochemistry gases and mantle derived gases. Hybrid gases are the mixture of gases from two or more origins., mixture of gases generated during different thermal evolution stages from the same source rock; mixture of gases generated from different source rocks; and mixture of inorganic gas and organic gas. The identification marks in common use for genetic types of natural gases mainly refer to the composition of natural gas, carbon isotopic composition of alkane and CO2, and parameters of light hydrocarbon. The carbon isotopic compositions are the most efficient tool and widely applied in gas typing.