珠江口盆地揭阳凹陷珠海组海底扇含气性检测与分析

揭阳凹陷是珠江口盆地近年划分出的无井新凹陷，烃类检测研究还是空白，多种技术的综合使用有利于提高地震烃类证据的可靠性.邻区白云凹陷的研究成果和揭阳凹陷三维地震资料解释出的构造、沉积和地层压力特征反映出该凹陷具有较好的油气生成和成藏条件.本文依据白云凹陷已发现的荔湾3-1气田所表现出的主频变化特征继而提出利用能量提前衰减来确定含气异常层位和异常区域的方法，即应用短时傅里叶变换，以5 Hz为间隔，将数据体分解成5 Hz、10 Hz、15 Hz、20 Hz、25 Hz、30 Hz的单频数据体；在了解含气层的主频与不含气层主频差异的前提下，通过比较相邻两个分频体的能量差异来获取异常衰减区域；以此检测出的含气能量衰减区域与荔湾3-1气田的分布范围颇为吻合，表明了该方法的有效性.地震资料解释出的揭阳凹陷珠海组底部海底扇在该方法的检测下亦表现出含气衰减，同时，检测出的衰减异常得到了AVO响应和正演模型的支持，它们一致反映出揭阳凹陷珠海组底部海底扇是一个具有勘探潜力的目标.

Detection and analysis to gas-bearing of seafloor fans in the Zhuhai Formation of the Jieyang sag,Pearl River Mouth Basin

The Jieyang sag is a new one divided recent years in the Pearl River Mouth Basin where no drilling well exists, and detection and research of hydrocarbon remain a blank. The reliability of seismic evidence of hydrocarbon indictors can be enhanced by integrated application of multiple technologies. With reference to the neighboring Baiyun sag, the structure, sediment and stratum pressure from interpretation of 3D seismic data show good hydrocarbon generation and accumulation conditions in the Jieyang sag. This paper proposes a method of identifying gas-bearing members and regions by energy attenuation in advance based on the variation of frequency in the Liwan 3-1 gas field. First, seismic data is decomposed into 5 Hz, 10 Hz, 15 Hz, 20 Hz, 25 Hz, and 30 Hz single frequency data volumes by short time window Fourier transform. Subsequently, relying on the diversity between dominant frequency of the gas-bearing layer and non-gas-bearing layer, the gas-bearing regions are identified by energy contrasts between the previous single frequency data and the later single frequency data. The abnormally attenuated area recognized through this method is turn out to be well consistent with the edge of the Liwan 3-1 gas field, which indicates this method is effective. The submarine fans of the lower member of Zhuhai Formation interpreted by seismic data in the Jieyang sag also exhibit obvious gas-bearing attenuation anomalies detected by this method. In addition, it is also supported by the analysis of the forward model and AVO response. These three pieces of gas-bearing evidence indicate the seafloor fans in the Jieyang sag are a target with exploration potential.