塔里木盆地古城台缘带寒武系丘滩体气藏形成特征

塔里木盆地古城台缘带寒武系丘滩体风险勘探首次发现气层，开拓了油气勘探的新领域。基于风险探井——城探1井钻探成果，在岩心观察、岩石薄片鉴定、地球化学分析等综合研究的基础上，结合测井和地震响应特征，对古城台缘带发育的4期寒武系丘滩体的油气成藏条件进行了分析。结果表明：寒武系丘滩体中天然气主要为古油藏的原油裂解气，原油成藏时间在加里东中、晚期，天然气成藏期在喜马拉雅期；丘滩体储层发育，主要由风化淋滤或有机酸的溶蚀作用形成，一般核部主体部位储集条件优于翼部；第一，二期丘滩体顶部发育直接盖层，分布稳定，储盖组合配置好，具有独立成藏条件。第三，四期丘滩体顶部具有不整合暴露剥蚀特征，直接盖层封盖能力较差，需要在寒武系上部区域盖层配合下规模成藏；古城台缘带断裂主要形成于寒武纪、中奥陶世、晚奥陶世3个时期，后期构造活动弱，有利于气藏保存。

Evolution of Cambrian mound-beach gas reservoirs in Gucheng platform margin zone,Tarim Basin

Gas has been discovered in the Cambrian mound-beach in the Gucheng platform margin zone of the Tarim Basin for the first time, opening up a new field of oil and gas exploration. The hydrocarbon accumulation conditions of four stages of Cambrian mound-beach in the Gucheng platform margin zone were analyzed based on core observation, cast thin section examination, geochemical analysis as well as logging and seismic data of exploration well CT 1. The results showed that the gas in the Cambrian mound-beach is mainly secondary gas from paleo-oil reservoirs. Oil accumulated during the middle and late Caledonian stage, which was cracked to gas during the Himalayan period. Mound-beach reservoirs formed due to weathering, leaching or organic acid dissolution, and the reservoir pro-perties of the central part is better than that of the periphery. On the top of the first and second stages of the mound-beach, direct caprock developed and configured well with the reservoir, which is favorable for independent accumulations. In the third and fourth stages, the top of mound-beach was exposed and eroded, and the sealing ability of direct cap rock is poor. The Upper Cambrian regional cap rocks are required for a useful reservoir. Fractures in the Gucheng platform margin zone mainly formed in the Cambrian, middle Ordovician and late Ordovician periods. Later tectonic activities were weak, which is favorable for gas accumulation.