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.