Subtle hydrocarbon reservoirs in Liu-1 Member of the Weixi'nan Sag,Beibuwan Basin,China

After high-resolution sequence stratigraphy was built,the authors studied the fine sedimentary facies and the oil source,trap conditions and formation of non-structural traps in the Liu-1 Member.The Liu-1 Member has abundant oil source,sufficient migration and charge of oil and gas,and excellent reservoir and cap association.The reservoirs include four types: fault-lithologic reservoir,unconformity reservoir,sandstone updip thinning out reservoir,and sand lens reservoir.The major reservoir layers are fan delta or delta sandy conglomerates.The characteristic of fault-lithologic traps is that fault strikes are normal to or intersect the direction of fan delta sources.The upriver sand bodies are eroded in unconformity traps.The downriver sandbodies uplift in sandstone updip thinning out traps.Sand lens lithologic traps are mainly formed by turbid sand distributed in deep lakes in the front of deltas.According to these characteristics,favorable targets are predicted.