南海北部天然气水合物气源系统与成藏模式

摘要

天然气水合物成矿成藏条件与油气成藏条件虽然存在差异，但亦存在共同之处，即均需要有充足烃源供给及烃源供给系统输送与有利聚集场所的时空耦合配置。为了深入研究天然气水合物与常规油气运聚成藏条件之差异，根据南海北部陆坡深水区构造沉积演化特点及油气地质条件与多年来油气及水合物勘探成果，综合剖析了油气及天然气水合物气源构成特点与流体运聚输导系统特征，同时根据地质地球物理及地球化学分析，初步研究了气源供给运聚通道系统类型与高压低温天然气水合物稳定带的时空耦合配置关系，并结合油气地质及天然气水合物成矿成藏基本地质条件，总结和建立了南海北部陆坡深水区“生物气源自生自储扩散运聚型”、“热解气源断层裂隙输导下生上储运移渗漏型”和“热解气源底辟及气烟囱输导下生上储运移渗漏型”等3种成因类型的天然气水合物成矿成藏模式，以期能为南海北部深水区天然气水合物资源预测及有利勘查目标评价优选等提供决策依据与指导。%Although differences exist in formation conditions between natural gas hydrate reservoirs and petroleum accumu-lation, they also have some requirements in common. Both of them need the spatiotemporal coupling configuration between sufficient hydrocarbon source supply, source supply transportation system and favorable gathering places. In order to further study the differences in formation conditions, this paper deeply analyzes the gas sources composition of petroleum and gas hydrate, and the characteristics of fluid migration transporting system, based on the tectonic sedimentary evolution, petroleum geological conditions, and oil, gas and gas hydrate exploration results of the northern South China Sea continental slope areas in the past. In addition, according to the analysis results of geology, geophysics and geochemistry, the space-time coupling con-figuration relationship between the types of gas migration channel system and the gas hydrate stability zone characterized by high pressure and low temperature are also dissected synthetically. Based on the basic geological conditions of oil/gas and gas hydrate reservoir, three models of natural gas hydrate formation and accumulation in northern slope deep-water area of South China Sea are summarized and established,“biogenic gas accumulated in place by way of self-generation and self-bearing”,“thermal gas accumulated offsite through faults and fractures by way of lower-generation and upper storage”, and“thermal gas accumulated offsite through mud diapir and gas chimney by way of lower-generation and upper storage”. This paper hopes to provide decision-making basis and guidance for the prediction of natural gas hydrate resources and the favorable exploration target evaluation in the deep water area of the northern South China Sea.