黔南坳陷平塘甘寨二叠系茅口组沉积相与储层特征分析

Sediemntary facies and reservoir characteristics in the Permian Maokou Formation in the Ganzhai section, Pingtang, southern Guizhou

关键词:  贵州平塘  黔南坳陷  茅口组  沉积相

Key words:  Pingtang in Guizhou  South Guizhou depression  Maokou Formation  sediemntary facies

摘要:

通过铸体薄片、物性测试、扫描电镜等资料,对黔南坳陷平塘甘寨二叠系茅口组沉积相与储层特征进行深入分析,认为贵州平塘甘寨茅口组主要的岩石类型为亮晶-微晶生屑灰岩、生物灰岩、微晶灰岩、内碎屑亮晶灰岩、硅质岩、瘤状灰岩和含燧石灰岩等。茅口组生物种类较多,有介形虫、腹足、腕足、三叶虫、藻类、棘屑、蜒、珊瑚、海百合茎等。上述岩石学特征和生物组合指示平塘甘寨地区中二叠统茅口组为开阔碳酸盐台地沉积环境,包括台内滩和滩间两个亚相。储层特征分析结果表明,茅口组储集空间以晶间溶孔和晶间孔为主,具有明显的低孔低渗特征。局部溶蚀孔、构造裂缝相对较发育,对改造储层的孔渗性有重要的贡献。储层类型为碳酸盐岩裂缝-孔隙型储层,储层质量及发育部位受沉积相、成岩作用和构造活动多因素的控制。

Abstract:

Sediemntary facies and reservoir characteristics in the Permian Maokou Formation in the Ganzhai section, Pingtang, southern Guizhou are dealt with on the basis of cast section, SEM and physical properties. The Permian Maokou Formation is dominantly made up of biosparite, biogenic limestone, micritic limestone, intrasparite, siliceous rocks, nodular and/or chert-bearing limestone. The organic fossils in the Formation contain ostracods, gastropods, brachiopods, trilobites, algae, echinoderms, fusulinids, corals and crinoids. All these evidences indicate an open carbonate platform environment of the Middle Permian Maokou Formation including the intraplatform shoals and intershoal subfacies. The reservoir spaces in the Maokou Formation are dominated by intercrystal solution openings and intercrystal pores, with low porosity and low permeability. The relatively developed dissolution pores and structural fissures may contribute a lot to the modification of the porosity and permeability of the hydrocarbon reservoirs. The types of the hydrocarbon reservoirs in the study area are represented by the fissure-porosity type carbonate reservoirs. The reservoir quality and position tend to be governed by sedimentary facies, diagenesis and tectonism.