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低渗凝析气藏的成藏机理是影响文昌A凹陷天然气勘探开发成效的关键问题。运用烃源岩地球化学、储层沉积学和成藏综合分析等方法,对天然气地质条件、气藏特征及成藏动态过程进行系统研究。得出如下新认识:①研究区下渐新统恩平组一段厚层湖沼相、滨浅湖相泥岩是主要的优质气源岩,该套烃源岩分别与恩平组二段、珠海组发育的(扇)三角洲相、潮坪相储层形成“自生自储”和“下生上储”2套成藏组合;②恩平组、珠海组储层埋深大于3 500m,孔隙度小于12%,渗透率小于1×10-3μm2,沉积微相和成岩作用控制了“甜点”储层的分布;③恩平组、珠海组储层“先致密、后成藏”致使油气的运移距离较短,具备“近源运移、晚期成藏”的特征。根据上述新认识提出2种成藏模式,即陡坡带垂向运聚模式和缓坡带垂向+侧向运聚模式,并指出北部缓坡带是下一步新领域拓展勘探的重要方向。
The mechanism of hydrocarbon accumulation in the low-permeability condensate gas reservoir is a key issue that affects the effectiveness of natural gas exploration and development in Wenchang A depression. This paper systematically studies the geological conditions of natural gas, the characteristics of gas reservoirs and the process of hydrocarbon accumulation by using the methods of geochemical, reservoir sedimentology and integrated hydrocarbon accumulation of source rocks. The following new understandings are obtained: (1) The thick Pleistocene lacustrine facies in the Lower Pleistocene Enping Formation in the study area is the main high-quality gas source rock, which is respectively connected with the second member of Enping Formation, Zhuhai Formation The developed (fan) delta facies and tidal flat facies formed two reservoir assemblages of “self-generative self-storage” and “subsistence upper reservoir”. ② The buried depths of Enping and Zhuhai formations were more than 3 500 m , Porosity less than 12%, permeability less than 1 × 10-3μm2, sedimentary microfacies and diagenesis controlled the distribution of “sweet ” reservoirs; ③ Enping Formation, Zhuhai formation reservoir Tibet “causes the hydrocarbon migration distance is shorter, with ” near source migration, late accumulation "characteristics. According to the above new understanding, two kinds of accumulation models are proposed, that is, vertical migration and accumulation mode of steep slope belt and vertical and lateral migration mode of gentle slope belt. It is pointed out that the northern gentle slope belt is an important direction to expand exploration in the new field in the next step.