Abstract: This paper focuses on the major characteristics of geochemical and geology in China's ever found medium-large gas fields with proved reserves above 100×10⁸m³.The natural gases can be categorized into three types, namely coal-formed gas, oil-type gas and biogenic gas on gas composition and carbon isotopes,of which the carbon isotopic values of ethane and other higher hydrocarbon gases may act as effective origin indicators.The main geological features are as follows;①strong gas generation inten sity, generally over 20×10⁸m³;②low-medium porosity and permeability, about 70% with porosity below 15%, and 88% with peameability from 0.1×103μm² to 500×10^-3 μm²;③maily structural traps which can be further divided into early-present, contemporary and late structures;④late period of gas generation in large quantity and reservoir formation, chiefly within Quaternary and Tertiary except for those originated from the lower Palaeozoic source rocks.

Key words: China, medium-large gas field, geochemistry geology

摘要： 对中国已发现的探明储量大于100×10⁸m³大中型气田的主要地球化学和地质特征进行了分析和总结;中国大中型气田的天然气可分为煤成气、油型气和生物气三种类型,各类天然气具有各自的组分和碳同位素特征,其中乙烷等重烃气的碳同位素是区分煤成气和油型气的有效指标。中国大中型气田的主要地质特征为:①强烃源充注,生气强度均大于20×10⁸m³/km²;②中、低孔渗储集层,孔隙率<15%的约占70%,渗透率为(0.1～500)×10^-3μm²的占88%;③以构造圈闭型为主,又可细分为早期或同期构造圈闭型和后期构造圈闭型;④生烃高峰期和成藏期较晚,除下古生界源岩形成的气田生烃高峰期和成藏期稍早外,其它气田均在第三纪和第四纪形成。

关键词: 中国, 大中型, 气田, 地化特征, 地质特征