The formation of hydrocarbon reservoirs is controlled by three major factors;lithological architecture, geological processes and energy-field environments. Among the three major factors, lithological architecture provides the storing medium for hydrocarbon; geological processes include hydrocarbon generation, migration, accumulation, preservation and modification; and energy-field environments refer to the various geothermal and geodynamic forces that affect the lithological architecture and drive the geological processes. In this study, we take Kela-2 and Sulige gas reservoirs as two examples to study relationships among the three major factors, and explain how these factors influence the scale and quality of hydrocarbon reservoirs. The formation of hydrocarbon reservoirs is controlled by three major factors; lithological architecture, geological processes and energy-field environments. Among the three major factors, lithological architecture provides the storage medium for hydrocarbons; geological processes include hydrocarbon generation, migration, accumulation, preservation and modification; and energy-field environments to to various geothermal and geodynamic forces that affect the lithological architecture and drive the geological processes. In this study, we take Kela-2 and Sulige gas reservoirs as two examples to study relationships among the three major factors , and explain how these factors influence the scale and quality of hydrocarbon reservoirs.