Sedimentary characteristics and accumulation model of sand-rich gas hydrate reservoir in the Qiongdongnan Basin, northern South China Sea

doi:10.13745/j.esf.sf.2024.6.52

Abstract

Abstract:

Sand-rich gas hydrate reservoirs are prime targets for hydrate exploration and test production worldwide. Concentrated hydrate in sand-rich reservoirs has been drilled in the Qiongdongnan Basin, northern South China Sea. Based on 3D seismic data, well logging, core samples, and test analysis, the large-scale accumulation of sand-rich gas hydrate has been confirmed. The sand-rich hydrate reservoir is characterized by low gamma ray, low sigma, high resistivity, increased P-wave and S-wave velocities, and a sharp reduction in T₂ spectrum signal amplitude. Additionally, high attenuation of P- and S-waves is observed in hydrate-bearing zones. The sand layer is distributed in a wedge-shaped horizontal sheet. The lithology is mainly coarse silt to fine sand, developed in the terminal lobe of deep-water turbidite systems. In vertical sections, gas hydrate and free gas exhibit co-layered distribution and lateral transition characteristics. In map view, the gas hydrate reservoir shows an elliptical distribution, with free gas concentrated in the center and gas hydrate developed in the periphery. Unlike gas hydrate reservoirs in dipping sands of other regions worldwide, the gas hydrate reservoir in the Qiongdongnan Basin was formed in a horizontal sand layer near the base of the hydrate stability zone. The formation of highly saturated hydrate was driven by locally high heat flow at the top of the underlying gas chimney and capped by overlying fine-grained sediments. A large area of hydrate was formed through radially lateral, long-distance migration of sufficient free gas from the center to the periphery.

Key words: sand-hosted hydrate, gas chimney, deep-water lobe deposits, lateral accumulation, Qiongdongnan Basin

CLC Number:

P618.13

REN Jinfeng, CHEN Yuhe, XU Mengjie, LI Tingwei, WANG Xiaoxue, LAI Hongfei, XIE Yingfeng, KUANG Zenggui. Sedimentary characteristics and accumulation model of sand-rich gas hydrate reservoir in the Qiongdongnan Basin, northern South China Sea[J]. Earth Science Frontiers, 2025, 32(2): 94-112.

Figures/Tables 14

Fig.1 Regional geological map and gas hydrate distribution of Qiongdongnan Basin

Fig.2 Sequence stratigraphic framework and associated sedimentary system in the study area

Fig.3 Logging characteristics of sand-rich hydrate-bearing formation and water-bearing formation in Well GMGS8-W05

Fig.4 Core photos of sand-rich hydrate-bearing reservoir and associated infrared measurement

Fig.5 The lithological classification and grain fraction of sediment cores obtained from 127.1-132.3 mbsf of Well GMGS8-W05

Fig.6 Calibration of well-seismic section in Well GMGS8-W05 and associated division of seismic stratigraphic units

Fig.7 Development features of sand-rich gas hydrate reservoir

Fig.8 Calibration of well-seismic section in Well GMGS6-W09 and associated division of seismic stratigraphic units

Fig.9 Calibration of well-seismic section in Well GMGS8-W22 and associated division of seismic stratigraphic units

Fig.10 The spatial distribution of the gas hydrate reservoir in relation to the channel-levee system

Fig.11 The horizontal distribution of the sand layer

Fig.12 Comparative analysis of Wells GMGS5-W07 and GMGS8-W05

Fig.13 Accumulation model of a co-layered distribution and a lateral transition of gas hydrate and free gas in the background of a gas chimney

Fig.14 Comparison of sedimentary characteristics of typical sand-rich gas hydrate reservoirs in the world sea (b) Modified after [9]; (c) Modified after [8]; (d) Modified after [39]; (e) Modified after [11].

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