【作者】 黄保家；

【导师】 肖贤明；

【作者基本信息】 中国科学院研究生院（广州地球化学研究所） ， 地球化学， 2002， 博士

【摘要】 本文针对制约莺琼盆地油气勘探中的一些关键性的地球化学问题，采用实际资料与模拟实验相结合、宏观与微观相结合的研究方法，深入地研究了天然气的成因类型和高温高压环境天然气的运移特征，进而探讨了超压与成藏的关系。 莺琼盆地至少存在4种主要天然气类型。其中，以产热成因气和无机CO₂为主，同时还有少量的生物气和混合气。细菌调查和生化成气模拟实验结果表明，生物气主要来源于第四系—上新统海相泥岩有机质中的粗纤维、半纤维素和蛋白质等细菌可利用基质，生化成气下限温度为85℃，突破了传统模式中的生物气下限温度为75℃门限。热成因气具有煤型气的特征，采用比较性分析和气源直接对比研究的新思路，可将其进一步划分为崖城天然气和莺歌海天然气两个亚类：前者主要源于渐新统崖城组含煤地层及浅海相泥岩，同时，西侧的莺歌海盆地有少量的贡献；后者则来自中新统梅山-三亚组海相泥岩。通过系统地剖析莺歌海底辟带气田无机CO₂的碳、稀有气体（氦）同位素特征与第三系及古生界基底的岩性及热源条件，结合热模拟实验资料，认为无机CO₂主要来深埋的梅山-三亚组钙质泥岩热分解和前第三系基底碳酸岩的热变质，这种钙质泥岩和碳酸岩热分解产生CO₂的初始温度大约为250℃，相当于埋深约6000m。 琼东南盆地崖城组和莺歌海盆地梅山-三亚组两套烃源岩含有大量的陆源有机质，构成了天然气生成雄厚的物质基础。盆地的高温地热效应特别是底辟带浅层由于深源热流体向上活动引起的“超前”熟化现象有利于天然气的生成，与高的地温作用相比，地层超压对本区腐殖型有机质热演化的抑制作用是次要。高温高压条件天然气成藏机制比较复杂，根据天然气的组成、同位素特征和储层包裹体分析，发现莺歌海东方1-1气田具有幕式充注、混合成藏的特征，由此揭示莺歌海盆地高压系统的幕式-快速运移导致排烃和聚集效率大大提高，是底辟正常压力带圈闭在极短的地质时期内天然气能够富集成藏的一个极其重要因素。储层包裹体古压力模拟结果表明，崖21-1构造储层的超压形成时间大约在中中新世—晚中新世（上新世早期的压力系数已达1.65），早于崖城组烃源岩大量生气阶段，因此妨碍了晚期天然气的大量充注，未形成商业价值气藏。更多还原

【Abstract】 The Ying- Qiong Basins in the north continental shelf of the South China Sea are in fact two separate Cenozoic basins with close geographic proximity and genetic linkage. Great attention has been paid to these basins in recent years because of their large sedimentary volumes and huge gas potentials. Geochemical and isotopic data of the natural gases from these basins have indicated the presence of at least four genetic types of gases in these basins. They are biogenic gas, thermogenic gas, gase with a mixed origin and inorganic CC^ gas. Biogas was generated from coarse fiber, hemicelluloses and protein that can be degraded by bacteria in Quaternary and Pliocene marine mudstone. The data from simulation test of source rocks, combined with the gas-measurement log and geothermal gradient data of the basins, has shown that the main stage of the bio-gas generation is between 35℃ and 65 ℃ and the death line of bio-gas is about 85 ℃. Using the methods of comparative analyses and gas-source direct correlation, it was suggested that thermogenic gases in the Ying-Qiong Basins were derived from two geographically separate petroleum systems. The gases in the Yinggehai Basin were likely from the marine shales in the Meishan-Sanya Formations within this basin, whereas gases in the Yacheng Field were mainly from the coal-bearing source rocks in the Yacheng Formation in the Qiongdongnan Basin, with only small amounts of gases with high inorganic CC>2 from the Yinggehai Basin. By studying the inorganic CO2 and helium isotopes in Yinggehai Basin, and investigating the Tertiary lithology and geothermal condition, combined with the results of thermal simulation test, it was suggested that inorganic CO2 gas principally came from thermal decomposition of Tertiary calcareous shales and Pre-Tertiary carbonate under the burial depth of 6000m, approximately at a strata temperature of about 250℃.The hydrocarbon source rocks in Yacheng Formation in Qiongdongnan Basin and Meishan and Shanya Formation in Yinggehai basin contain a dominant amount of terrestrial organic matter. This study has indicated that the overpressure cannot significantly delay the organic thermal maturation of the source-rock. However, the high temperature conditions have had strong influence on the thermal evolution and hydrocarbon generation of the source rocks. In places where the source rocks were intensely influenced by deep sourced hot fluids, the rapid heating resulted in an advanced maturation of organic matter deposited in shallower depth. It is the hightemperature, combined with relatively abundant humic organic matter in the Miocene and Yacheng Formation source rocks, that led to predominantly abundant natural gases in the Ying-Qiong basins. Moreover, the focused-episodic gas migration significantly increased the hydrocarbon expulsion efficiencies of the source rocks, and thus provided favorable conditions for the accumulation of large amounts of gases in the diapric structures (such as Dongfangl-1 gas field) in very short geological time. PVT simulation results of fluid inclusions have revealed that an overpressure formed in middle or late Miocene in Yacheng21-l structure, earlier than the phase of enormous hydrocarbon generation and migration of the Yacheng source rock. This overpressure has stopped migration of the later-generating gases into the reservoir, having led to only small amount of aqueous gas in the reservoir.更多还原