南海北部陆坡天然气水合物钻探发现及成藏特征

doi:10.13745/j.esf.sf.2024.6.56

摘要/Abstract

摘要：

天然气水合物因其潜在的能源价值而备受关注,我国自20世纪90年代开始在南海开展水合物调查,截至目前已实施了9个水合物钻探航次,取得了一系列水合物找矿突破。钻探结果证实,南海北部发育多种类型水合物,神狐海域主要发育扩散型水合物,东沙海域发育复合型水合物,琼东南发育渗漏型及砂质型水合物。本文结合钻探成果,详细阐述了各种类型水合物的地震反射特征以及测井响应特征。扩散型天然气水合物在地震上主要表现为显著的BSR以及BSR之上的强正极性反射,在测井上主要表现为高电阻率、高纵波速度和高横波速度,如出现水合物与游离气共存的混合层则在测井上表现为高电阻、低纵波速度、高横波速度和中子-密度反交等特征。渗漏型水合物在地震上通常不发育典型的BSR,BSR之上发育亮点反射或者浅部地层发育上拉反射以及柱状的空白反射,海底发育显著的异常地貌,如丘状体和麻坑,在测井上表现为极高的电阻率、稍微增高的纵波及横波速度、高角度层理等特征。砂质水合物在地震上表现为极强的BSR和指示砂质水合物的强正极性反射,测井上表现为低伽马、极高的电阻率、极高的纵横波速度、略微增高的密度和略微降低的中子孔隙度等特征。最后总结了神狐及琼东南水合物成藏控制因素,认为神狐海域发育的深大断裂以及倾斜的天然堤沉积控制了神狐海域高丰度天然气水合物藏的发育,而琼东南海域水合物发育受古潜山及差异压实作用控制。

关键词: 水合物钻探, 扩散型水合物, 渗漏型水合物, 砂质水合物, 南海北部

Abstract:

Gas hydrates have garnered significant attention due to their potential as an energy resource. Since the 1990s, China has been conducting gas hydrate investigations in the South China Sea, with the Guangzhou Marine Geological Survey leading nine drilling expeditions that have achieved notable breakthroughs in gas hydrate exploration. These drilling results confirm the occurrence of various types of gas hydrates in the northern South China Sea. Diffusion gas hydrates are prevalent in the Shenhu area, vent and sandy gas hydrates are primarily found in the Qiongdongnan area, and complex gas hydrates are present in the Dongsha area. This paper integrates drilling results to describe the seismic reflection and logging response characteristics of these gas hydrate systems. The diffusion gas hydrate system is characterized by a prominent bottom simulating reflector (BSR) and strong positive polarity reflections above the BSR in seismic data. Logging data reveals high resistivity, high P-wave velocity, and high S-wave velocity. In the mixed layer, where gas hydrate coexists with free gas, logging data show high resistivity, low P-wave velocity, high S-wave velocity, and a neutron-density crossover. The vent gas hydrate system typically lacks a distinct BSR but exhibits bright reflections above the BSR, pull-up reflections, and columnar blanking reflections in shallow strata on seismic data. Additionally, anomalous geomorphological features such as seafloor mounds and pockmarks are commonly associated with vent gas hydrate systems. Logging data for vent gas hydrates shows extremely high resistivity, slightly increased P-wave and S-wave velocities, and significant changes in bedding dip and/or azimuth. Sandy gas hydrates are identified by very strong BSRs and strong positive polarity reflections on seismic data, indicating the presence of sandy reservoirs. Logging data for sandy gas hydrates are characterized by low gamma-ray values, very high resistivity, very high P-wave and S-wave velocities, slightly increased density, and decreased neutron porosity. The study also summarizes the controlling factors for gas hydrate formation in the Shenhu and Qiongdongnan areas. In the Shenhu area, the development of concentrated gas hydrate reservoirs is primarily controlled by deep, large faults and inclined levee deposits. In contrast, gas hydrate formation in the Qiongdongnan area is influenced by paleoburied hills and differential compaction.

Key words: gas hydrate drilling, diffusion gas hydrate, vent gas hydrate, sandy gas hydrate, northern South China Sea

中图分类号:

匡增桂, 任金锋, 邓炜, 赖洪飞, 谢莹峰. 南海北部陆坡天然气水合物钻探发现及成藏特征[J]. 地学前缘, 2025, 32(2): 1-19.

KUANG Zenggui, REN Jinfeng, DENG Wei, LAI Hongfei, XIE Yingfeng. Drilling discoveries and accumulation characteristics of gas hydrate in the Northern Slope of South China Sea[J]. Earth Science Frontiers, 2025, 32(2): 1-19.

图/表 15

图1 南海北部天然气水合物钻探航次位置图 GMGS7航次因天气原因而中止。

Fig.1 Locations of gas hydrate drilling legs in the northern South China Sea. Expedition of GMGS7 was halted due to bad weather.

图2 GMGS1航次过井地震剖面图

Fig.2 Seismic profiles across wells drilled in GMGS1

图3 GMGS3-4航次过井地震剖面图

Fig.3 Seismic profiles across wells drilled in GMGS34

图4 SH-W17-2015井水合物及游离气测井响应特征

Fig.4 Logging response of gas hydrate and free gas in SH-W17-2015

图5 GMGS2航次过井地震剖面图

Fig.5 Seismic profiles across wells drilled in GMGS2

图6 GMGS5航次过井地震剖面图

Fig.6 Seismic profiles across wells drilled in GMGS5

图7 QDN-W09-2018井水合物测井响应特征 a—62-63 mbsf (取样位置见左图红色方框),b—102-103 mbsf为保压岩心样品CT扫描成像。

Fig.7 Logging response of gas hydrate in QDN-W09-2018 a—62-63 mbsf (The location of the sample is indicated as a red box on the left), b—102-103 mbsf are CT images of pressure cores.

图8 GMGS6-9航次过井地震剖面图

Fig.8 Seismic profiles across wells drilled in GMGS6-9

图9 QDN-W20-2021井水合物测井响应特征

Fig.9 Logging response of gas hydrate in QDN-W20-2021

图10 神狐海域深大断裂特征及其流体运移模式

Fig.10 The characteristics of dee-prooted faults and fluids migration model in Shenhu area

图11 神狐海域断层、气烟囱及BSR分布及钻井位置图

Fig.11 The distribution of fault, gas chimney and BSR and the locations of the drilling wells in Shenhu area.

图12 神狐海域试采矿体构造-沉积耦合控矿模式

Fig.12 The coupling structuresedimentary control model in Shenhu gas hydrate accumulation where gas hydrate production test has been carried out in 2017 and 2020

图13 琼东南海域水合物稳定带均方根振幅属性图

Fig.13 RMS (root mean square) seismic amplitude attribution map of the base of gas hydrate stability zone in Qiongdongnan area

图14 琼东南海域W09矿体流体运移模式

Fig.14 The model of fluid flow in W09 gas hydrate accumulation in Qiongdongnan area

图15 琼东南海域W08矿体流体运移模式

Fig.15 The model of fluid flow in W08 gas hydrate accumulation in Qiongdongnan area

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