辽河盆地古近系水下喷发粗面岩相模式及其储层意义

Facies architecture of Paleogene subaqueous trachytes and its implications for hydrocarbon reservoirs in Liaohe Basin

关键词:  粗面岩  火山岩相  相模式  水下喷发  火山岩储层  辽河盆地

Key words:  trachyte  volcanic facies  facies architecture  subaqueous eruption  volcanic reservoir  Liaohe Basin

摘要:

以辽河盆地东部凹陷古近系水下喷发粗面岩为例,研究粗面岩岩相分类、相序与相模式,分析其优质储层控制因素与分布规律;通过单井相分析和连井岩相对比,将粗面岩划分为5相11亚相,建立粗面岩火山机构的相模式。结果表明:火山口—近火山口相带以侵出相发育为标志,过渡相带以爆发相火山碎屑流亚相为主,边缘相带主要由爆发相空落亚相和火山沉积相构成,纵向相序以爆发相→侵出相、火山通道相→侵出相两类为主,自中心向边缘的平面相序为火山通道相与侵出相→溢流相与爆发相→火山沉积相;水-岩浆反应产生的淬火和爆发作用是水下喷发粗面岩岩相空间分布和储层有效性的关键影响因素;与角砾状粗面岩类的岩石组构相关的粒内溶孔和残余粒间孔-填隙物溶孔构成有效孔隙的主体,粒内斑晶溶孔和基质溶孔对储集性能贡献最大,合计占53.2％,构造裂缝对渗透性能起控制作用;侵出相外带亚相、爆发相火山碎屑流亚相和火山通道相火山颈亚相是粗面岩发育的3类优质储层,其平均孔隙度大于10.3％,渗透率大于0.35×10-3μm²,应作为粗面岩油气藏勘探的首要目标。

Abstract:

The Paleogene trachytes in the Eastern Sag of Liaohe Basin were dominantly erupted and emplaced in subaqueous settings. Borehole data and seismic profiles were used to study the facies classification, sequence and architecture of these trachytic rocks, and to reveal the distribution of high-quality reservoirs and their controlling factors. Five principal volcanic facies and eleven sub-facies can be identified in the trachytic successions by means of facies analysis on both boreholes and cross-sections. A representative facies model was proposed for volcanic facies analysis and prediction, which reveals three volcanic facies associations corresponded to the proximity to volcanic conduit. Respectively, the central-proximal facies association is dominated by extrusive lava rocks, while the medial facies association is characterized by pyroclastic flow deposits, and the distal facies association is composed of water-settled fall deposits and volcaniclastic deposits. Two vertical facies sequences from bottom to top are explosive to extrusive facies and volcanic conduit to extrusive facies, respectively. Lateral facies sequence from volcanic center to edge can be described as the volcanic conduit and extrusive facies combination, the effusive and explosive facies combination, and the volcaniclastic facies. Quenching fragmentation and volcanic explosion resulted from mingling of magma and water are considered to be the key influencing factors to the characteristics of volcanic facies and reservoirs of subaqueous trachytes in the study area. Intra-particle dissolution pores, residual inter-particle pores and the related inter-particle cement dissolution pores are proven to be the most important valid porosities in trachytic reservoirs. The intra-particle phenocrystal and matrix dissolution pores, especially, make the major contribution to reserve capacities which account for 53.2％ in total, while the permeability is determined by tectonic fractures. Three principal types of high-quality reservoirs with average porosity larger than 10.3％ and permeability larger than 0.35×10-3 μm² are developed in outer extrusive sub-facies, pyroclastic flow sub-facies and volcanic diatreme sub-facies, which should be taken as the major exploration targets of the subaqueous trachytic successions.