运用地质、地球化学正反演相互印证的方法，对元坝气田长兴组礁滩相岩性气藏天然气的成因与来源及形成演化进行了系统研究。结果表明：元坝气田长兴组礁滩相岩性气藏天然气主要为古油藏原油裂解气，部分气源直接来自烃源岩；晚三叠世—早侏罗世，原油沿层间缝和节理缝运移至储集层，形成古油藏；晚侏罗世—晚白垩世古油藏裂解，天然气沿裂缝－孔隙型储层二次运移与聚集，形成古气藏；晚白垩世以来，天然气进一步调整运移，现今气藏形成。现今气藏经历了物理调整改造与天然气组分的化学改造，元坝气田西北部小幅度抬升，埋藏深度相对较浅，TSR 反应程度较东部变弱。

The origin, source and evolution of the reef flat facies lithologic gas reservoir of Changxing Formation in Yuanba Gas Field were studied systematically by themethods of geologic and geochemical inversion. The result shows that the gas of the reel flat facies lithologic gas reservoir is mainly from the oil cracked gas of paleo-reservoir, and a small part of the gas is directly from the source rock of Upper Permian. During Late Triassic-Early Jurassic, crude oil migrated to reservoir along the interlayer fractures and joint fissures, and formed paleo-reservoir. During Late Jurassic-Late Cretaceous, the paleoreservoir cracked, gas migrated along fractures and pore reservoir and accumulated, and formed paleo-gas reservoir. Since Late Cretaceous, gas further migrated and formed the present gas reservoir. The gas reservoir experienced physical adjustment and chemical alteration of natural gas component. Small amplitude of uplift in the northwestern Yuanba Gas Field leads to the relatively shallow burial depth and the weak TSR response.