西沙群岛中新世藻礁白云岩植物格架、储层特征和成礁模式

The framework,reservoir characteristics and reef formation model of Miocene algal reef dolomite in the Xisha Islands

传统生物礁成因理论质疑钙藻形成坚固生物礁抗浪结构的能力,将钙藻归类于附礁生物群落。文章利用微焦X射线扫描成像技术(X-CT),研究“西科1井”、“西永2井”中新世红藻珊瑚藻科南海奇石藻(新种)格架岩和绿藻仙掌藻节片岩岩芯。通过三维层析成像直观透视图像,发现钙藻生物营造的藻礁抗浪结构,包括典型红藻柱状格架结构、障积结构和绿藻仙掌藻节片结构,证实钙藻植物是主要的造礁造岩生物。通过三维孔隙重构,获得总孔隙体积、面孔率、孔隙度的物性参数,验证了藻礁是南海沉积盆地中新世重要的油气储集层。提出了藻礁成因模式:造礁钙藻适应海面升降逐步演替–取代,经过钙化–埋藏化石化–白云石化,沉积生成藻礁云岩,造成中新世西沙礁纵向序列的增长。

Traditional bioreef genesis theory either lacks evidences for algae forming strong bioreef anti-wave frameworks or attributes them to an accessory reef biotic community.In this paper,microfocal X-ray(X-CT)scanning imaging technology is used to study the core of the Aethesolithon nanhaiensis reef framework rocks and Halimeda reef proglottid rocks of Miocene age in Wells Xike 1 and Xiyong 2.Through three-dimensional tomography visual perspective images,it was found that the wave resistance structure of algal reef created by calcareous algal organisms,including typical Aethesolithon nanhaiensis reef framework structure,baffle-structure rocks and Halimeda reef proglottid structure.It also verifies that algal reefs are important Miocene oil-gas reservoirs in the South China Sea depositional basins by quantifying the throat,areal porosity and porosity parameters using threshold approach.Besides,the genetic model of algal reef is put forward:the reef-building calcium algal algae adapted to the sea level rise and fall gradually succession-replacement,and after calcification,burial and fossilization,dolomitization,sedimentary algal reef dolomitization,resulting in the growth of the longitudinal sequence of the Xisha Reef in Miocene.