珠江口盆地陆丰凹陷深层砂岩储层特征及主控因素

珠江口盆地陆丰凹陷深层碎屑岩储层埋深普遍大于3 000 m，储层质量较差且非均质性强，制约油气高效勘探。综合运用岩心、薄片鉴定、物性测试、压汞测试以及测录井等分析手段，对陆丰凹陷古近系文昌组和恩平组深埋碎屑岩开展了储层岩石学特征、成岩作用及优质储层主控因素研究。研究表明，古近系文昌组岩石类型为岩屑质石英砂岩，储层孔隙主要由原生孔和次生孔构成，表现为一套特低-低孔隙度（平均孔隙度为9.42%）、超低-低渗透率（平均渗透率为8.38 mD）储层特征；恩平组储层主要由长石岩屑质石英砂岩构成，储层总体属于低-中孔隙度（平均孔隙度14.66%）、低-中渗透率储层（平均渗透率为198.43 mD），以原生孔为主。在3 600~4 400 m深度段，发育一套高孔隙度的优质储层带，主体为原生孔，可见大量次生溶蚀孔隙，孔隙度可达20%，渗透率可达263.74 mD。这套优质储层形成条件包括：①先天条件好，长距离搬运的辫状河三角洲前缘中厚层砂体，具备岩性较粗、石英含量高、杂基含量低和结构成熟度高的特征，保留了较多的原生孔隙；②与生烃液态窗埋深对应良好，有机酸易对储层中长石和岩屑产生强烈溶蚀，明显改善了储层物性；③油气充注发生在长石和岩屑溶蚀之后、晚期碳酸盐胶结物大量形成之前，是优质储层得以保存的又一重要条件。总体而言，沉积条件、溶蚀作用和油气充注时间三者的良好匹配是深层优质储层形成的根本原因。这些认识对于珠江口盆地深层油气勘探以及相似地质背景的优质储层预测具有一定的启示作用。

Reservoir characteristics and main controlling factors of deep sandstone in Lufeng sag,Pearl River Mouth Basin

The Lufeng sag of Pearl River Mouth Basin is characterized the deep clastic rock reservoir generally with a burial depth greater than 3 000 m, poor quality and high heterogeneity, thus restricting the efficient exploration of oil and gas. Comprehensively using the technical analysis methods such as core and thin section identification, physical property test, mercury intrusion test and logging, this paper studies the reservoir petrological characteristics, diagenesis and main controlling factors of high-quality reservoirs in the deep-buried clastic rocks of Paleogene Wenchang Formation and Enping Formation in Lufeng sag. The study shows that the Paleogene Wenchang Formation is dominated by lithic quartz sandstone, and the reservoir pores are mainly composed of primary and secondary pores, characterized by a set of ultra low-low porosities (average porosity of 9.42%) and ultra low-low permeabilities (average permeability of 8.38 mD). Enping Formation is mainly composed of feldspar lithic quartz sandstone, and the reservoir has generally low-medium porosity (average porosity of 14.66%) and low-medium permeability (average permeability of 198.43 mD), dominated by primary pores. In the depth range of 3 600-4 400 m, a set of high-quality reservoirs with high porosity is developed, dominated by primary pores. This study also detects a large number of secondary dissolution pores with the porosity of 20% and the permeability of 263.74 mD. The formation conditions of this set of high-quality reservoir include:(1) the medium-thick sand body of well-developed braided river delta front formed through long-distance transport with the characteristics of coarse lithology, high quartz content, low heterogeneous content and high structural maturity, retaining more primary pores. (2) it well corresponds to the buried depth of hydrocarbon-generation liquid window, and organic acid is prone to cause strong corrosion of the feldspar and cuttings in reservoir, significantly improving the reservoir physical properties. (3) oil and gas charging occurs posterior to feldspar and clastic dissolution but prior to the formation of many carbonate cements in the later period, which is another important condition for preserving high-quality reservoirs. In general, the good matching of sedimentary conditions, dissolution and hydrocarbon charging time is the root cause for the formation of high-quality deep reservoirs. Obviously, these insights have significant implications for deep oil and gas exploration in Pearl River Mouth Basin and high-quality reservoir predictions under similar geological settings.