南海珠江口盆地陆丰凹陷文昌组沉积成岩特征及储层物性控制因素

Sedimentary diagenetic characteristics and controlling factors of reservoir physical properties of Wenchang Formation in Lufeng Sag, Pearl River Mouth Basin, South China Sea

摘要

为明确陆丰凹陷深部储层特征及成因机制,对凹陷南部地区7口井文昌组岩心样品进行薄片鉴定、FE-SEM观察、XRD分析及物性测试。结果表明:文昌组岩石类型为长石石英砂岩、岩屑石英砂岩、岩屑砂岩和少量石英砂岩,杂基以泥质和凝灰质为主,胶结物以自生石英、泥晶碳酸盐和自生高岭石为主。储层物性非均质性强,孔隙度为2.2%~21.6%,平均为12.0%,以次生孔隙为主;渗透率小于10×10^-3μm²的占比达95%,呈特低-低-中孔隙度、低-特低渗透率特点。文昌组主要发育三角洲、辫状河三角洲和扇三角洲3种沉积相,包括三角洲前缘、辫状河三角洲前缘和扇三角洲前缘3种亚相及6种沉积微相。辫状河三角洲的储层孔隙度相对较高,渗透率相对居中;扇三角洲的储层孔隙度居中,渗透率相对较高;三角洲的储层孔隙度与扇三角洲的相似,渗透率相对最低;辫状河三角洲水下分流河道砂体更利于发育优质储层。文昌组砂岩经历早成岩阶段A、B期、中成岩阶段A、B期;压实-压溶作用较强,导致原生孔隙不发育;不同类型、不同期次的胶结作用抑制储层物性;长石、凝灰质和岩屑的溶蚀作用形成次生孔隙及次生矿物,孔隙度提高,但渗透率无明显提升。该结果对陆丰凹陷文昌组后续勘探开发提供基础支撑。

Abstract

In order to study the characteristics and genetic mechanism of deep reservoirs in Lufeng sag. Thin section identification, FE-SEM observation, XRD analysis and physical property measurement were carried out on the core samples of Wenchang Formation from 7 wells in the southern part of the depression. The results show that the rock types of the Wenchang Formation are feldspar quartz sandstone, lithic quartz sandstone, lithic sandstone and a small amount of quartz sandstone. The complex base is mainly argillaceous and tuffaceous. The cement is mainly authigenic quartz, micrite carbonate and authigenic kaolinite. The physical properties of the reservoir are complex and varied, with porosity ranging from 2.2% to 21.6%, with an average value of 12.0%. It is dominated by secondary pores. The permeability of less than 10×10^-3μm² accounted for 95%, forming the characteristics of ultra-low-low-medium porosity and ultra-low permeability. The Wenchang Formation mainly develops three sedimentary facies: delta, braided river delta and fan delta, including three subfacies of delta front, braided river delta front and fan delta front and six sedimentary microfacies. The reservoir porosity of braided river delta is relatively high, and the permeability is relatively medium. The reservoir porosity of fan delta is in the middle, and the permeability is relatively high. The reservoir porosity of normal delta is similar to that of fan delta, and the permeability is relatively the lowest. The underwater distributary channel sand bodies are more conducive to the development of high-quality reservoirs in the braided river delta. The sandstone of Wenchang Formation has experienced early diagenesis stage A and B, middle diagenesis stage A and B in the study area. The strong compaction-pressure solution leads to the undeveloped primary pores. Different types and different stages of cementation inhibit reservoir physical properties. The dissolution of feldspar, tuff and debris forms secondary pores and secondary minerals and increases porosity, but does not significantly increase permeability. This result provides basic support for the subsequent exploration and development of Wenchang Formation in Lufeng Sag.

关键词

珠江口盆地 / 陆丰凹陷 / 文昌组 / 沉积成岩特征 / 储层物性 / 控制因素

Key words

Pearl River Mouth Basin / Lufeng Sag / Wenchang Formation / sedimentary diagenetic characteristics / reservoir physical propertie / controlling factors

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基金资助

中海石油“十四五”重大科技项目(CCL2022SZPS0323)

天津市大学生创新创业项目(202310792032)