Large Gas Fields and Their Significance in the Natural Gas Industry 1 CHAPTER OUTLINE 1 Large Gas Fields and Their Important Roles 1 1.1 Classification Criteria of Large Gas Fields 1 1.2 Large Gas Field-An Important Foundation for a Great Gas-Producing Country 2 1.2.1 Large Gas Fields Change China from a Poor Gas Producer to a Great Gas Producer3 1.2.2 Large Gas Fields Make Russia the “Saudi Arabia of Natural Gas” 6 2. Geological and Geochemical Characteristics of Large Gas Fields in China 10 2.1 Geochemical Characteristics 10 2.1.1 Natural Gas Components 10 2.1.2 Natural Gas Sources 11 2.2 Geological Characteristics 23 2.2.1 Reservoir 23 2.2.2 Gas Accumulation Stages 27 2.2.3 Gas Reservoir Types 29 References 31