Reservoir Characteristics and Exploration Implications of Gas Hydrate Enrichment Area, Qiongdongnan Basin
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摘要: 天然气水合物是海洋新能源的重要开拓领域,南海琼东南盆地是水合物富集区和热点研究区.为进一步摸清琼东南水合物富集区储层特征,选取国产自主技术装备收获的水合物岩心开展分析并获得第一手资料.通过粒度、岩矿分析(含扫描电镜)、随钻测井、红外热成像、氯离子饱和度法等综合分析,测得储层主要是由石英(含量23%)、斜绿泥石(含量17%)、绢云母(含量15%)、钠长石(含量14%)等组成的硅铝质粘土沉积,储层粒度中值15.1~34.1 μm,饱和度分布3%~54%,揭示了水合物储层“细粒性、未成岩、易溃散、高电阻、高声速、强非均质性”等六大特征;结合气源、储层分析和勘探认识,建立了“异地热成因气充注、本地微生物成因气补充、气烟囱顶部运移聚集、海底扇内横向成藏”的成藏模式,重点对123 mbsf和153 mbsf(mbsf全称为meter below seafloor,表示海底以下深度,以“m”为单位)两件原位保压岩心进行X射线和CT扫描,识别出泥质粉砂孔隙型储层(海底扇横向为主)和南海新发现的水合物储层类型泥质粉砂微裂缝型储层(气烟囱垂向为主)两类主要储层;提出了“以古气候-地质事件为节点关注珠江口-琼东南第四系大型砂体的赋存条件和资源潜力、加强传热传质在水合物成藏机理和资源评价中的研究”勘探启示.研究可为中国南海天然气水合物勘查和试采提供重要科学参考.Abstract: Gas hydrate is an important development of marine new energy, and the Qiongdongnan basin of the South China Sea is a hydrate enrichment and hot research area. In order to further understand hydrate reservoir characteristics of the Qiongdongnan area, thermal insulation and pressuring coring sampled by domestic technical equipment were selected for analysis and first-hand data were obtained. By comprehensive analysis of grain size, rock and mineral analysis (including electron microscope scanning), LWD, thermal imaging, chloride ion saturation method, etc., it is measured that the reservoir is mainly composed of siliceous and aluminous clay deposits composed of quartz (23% content), plagioclase (17% content), sericite (15% content), albite (14% content), etc., and the median grain size of reservoir is 15.1 μm to 34.1μm and the saturation distribution is 3% to 54%. It reveals six characteristics of hydrate reservoir: "fine-grained, unconsolidated, easily disintegrate and disperse, high resistance, high acoustic velocity, and strong heterogeneity". Combined with gas source, reservoir analysis and exploration knowledge, a reservoir formation model of "off-site thermogenic gas injection, local microbial gas supplement, accumulation at top of gas chimney, and horizontal formation in the submarine fan reservoir" has been established. Focusing on the X-ray and CT scanning of 123 mbsf and 153 mbsf in-situ pressure-retaining cores, two main types of reservoirs are identified: argillaceous silt pore-type reservoir (submarine fan) and argillaceous silt micro-fractured reservoir (gas chimney fluid reconstruction), a new discovered type of hydrate reservoirs in the South China Sea. Exploration inspirations are put forward, "study the occurrence and resource potential of shallow scaled sand-bodies of geological events in the Zhujiangkou and Qiongdongnan sea, and strengthen research on heat and mass transfer of reservoir formation mechanism and resource evaluation".The research will provide important scientific reference for hydrate research and production test of the South China Sea.
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表 1 琼东南盆地H1井水合物储层中位粒度
Table 1. Median particle size distribution of reservoir samples of Well H1 in the Qiongdongnan basin
深度(m) 粒度中值(μm) 0.10 24.856 0.50 27.641 0.80 34.112 0.95 24.600 11.20 24.760 12.30 21.312 27.20 15.055 87.20 16.710 100.70 17.946 123.00 30.642 127.20 27.784 129.70 28.944 137.20 21.804 153.00 15.962 172.00 25.555 表 2 琼东南盆地水合物样品饱和度估算结果
Table 2. Saturation estimation results of hydrate reservoir in the Qiongdongnan basin
样品号 取样深度(m) 氯离子浓度(104 mg/L) 电导率(ms/cm) 氯离子估算饱和度(%) 1 11.2 1.66 58.63 18.10 2 27.2 1.49 53.82 27.16 3 67.2 1.85 53.20 7.30 4 87.2 1.76 52.42 12.35 5 97.2 1.98 51.00 饱和度基准 6 100.7 3.43 68.19 饱和度基准 7 123 2.28 38.28 37.25 8 129.7 2.82 39.67 19.76 9 137.2 3.08 62.3 11.34 10 153 1.74 82.86 54.75 注:氯离子浓度计算公式为S=(1-Clpw/Clsw)/ρh,其中ρh指天然气水合物密度,Clpw指实测氯离子浓度,Clsw指基线氯离子浓度. -
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