关键词: 中国, 大中型, 气田, 地化特征, 地质特征

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