珠江口盆地惠南半地堑恩平组烃类充注特征与砂岩致密化成因分析

Hydrocarbon charging characteristics and sandstone densification genesis of Enping Formation in Huinan half-graben,Pearl River Mouth basin

珠江口盆地惠州凹陷惠南半地堑A构造A1井古近系恩平组砂岩见油气显示,但地层测试结果为干层,砂岩具有低孔低渗特征。通过生物标志化合物绝对定量分析、岩石薄片、阴极发光、扫描电镜、X衍射、流体包裹体、储层定量荧光分析、成岩演化模拟等手段,对A1井恩平组砂岩中烃类充注史和储层成岩作用过程与致密化成因进行了综合分析。生物标志化合物组合特征指示A1井恩平组储层中以自生自储烃为主,有少量文昌组烃源岩生成的烃类贡献;流体包裹体和颗粒荧光定量分析指示2.5～0 Ma是油气主充注期,以晚期充注为主。石英胶结是导致A1井区恩平组砂岩致密化的主要原因,埋藏成岩期为富K+流体环境,高岭石和钾长石向伊利石转化,形成石英胶结和伊利石,破坏了砂岩的孔渗性;恩平组砂岩储层具有典型的先致密后烃类充注的特征,石英和伊利石均为水湿性矿物,烃类充注对胶结物的形成抑制作用不大。本文研究结果可为珠江口盆地古近系深层油气成藏研究提供参考。

The oil and gas shows are found in the sandstone of Paeogene Enping Formation in Well A1,which is located in the A structure of Huinan half-graben in Huizhou sag of Pearl River Mouth basin.However,the formation test results show it is a dry layer,and the sandstone is of low porosity and low permeability.Through a series of analysis methods,including absolute quantitative analysis of biomarker compounds,rock slices,cathodoluminescence,scanning electron microscopy,X-ray diffraction,fluid inclusions,reservoir quantitative fluorescence analysis,diagenetic evolution simulation,the hydrocarbon charging history,diagenesis process and densification genesis of the sandstone of Enping Formation in Well A1 were comprehensively analyzed.The biomarker compound characteristics indicate that the accumulation model of Enping Formation in Well A1 was mainly generated in the form of self-generation and self-accumulation,with a small amount of hydrocarbon contribution from Wenchang Formation source rocks.Quantitative analysis of fluid inclusions and particles shows that 2.5~0 Ma is the main charging oil and gas period and hydrocarbon accumulation was dominated by late charging.Quartz cementation is the main cause for the densification of the sandstone in Enping Formation in Well A1.The K+rich fluid environment during the diagenetic period promoted the conversion of Kaolinite and K-feldspar to illite,forming quatz cement and illite,which destroyed porosity and permeability of the sandstone.The sandstone reservoirs of Enping Formation are characterized by typical early dense and hydrocarbon charging in the later period.Both quartz and illite are water-wet minerals,and hydrocarbon charging has little inhibitory effect on the formation of cement.The results of this paper can provide reference for the study of Paleogene deep hydrocarbon accumulation in Pearl River Mouth basin.