珠江口盆地流花油田新近系生物礁灰岩储层特征及成因分析

南海珠江口盆地东沙隆起流花油田新近系灰岩储层为典型的台地边缘生物礁储层。岩石类型包括皮壳状珊瑚藻黏结灰岩、缠绕状珊瑚藻-珊瑚骨架灰岩、泥晶有孔虫-珊瑚藻颗粒灰岩、亮晶有孔虫-珊瑚藻颗粒灰岩、含红藻石灰岩、泥晶珊瑚颗粒灰岩、生屑泥晶灰岩7类。孔缝类型丰富,包括泥晶基质溶孔、粒间溶孔、藻架溶孔、粒内溶孔、铸模孔、体腔孔、晶间微孔7类孔隙及溶蚀缝、珊瑚藻皮壳间隙缝、似缝合线溶蚀缝、构造缝4类裂缝。划分了孔洞-网状裂缝型、孔隙型、裂缝-孔洞型、致密裂缝型4种储集类型。皮壳状珊瑚藻灰岩属于孔洞-网状裂缝型储层,泥晶颗粒灰岩、含红藻石灰岩和红藻石灰岩属于孔隙型,珊瑚骨架灰岩属于裂缝-孔洞型,亮晶生屑灰岩和胶结作用较强的皮壳状藻灰岩属于致密裂缝型。沉积微相和成岩作用控制了不同储集类型的分布,生物礁形成过程中的多期暴露对沉积微相和储集空间有重要影响。沉积-成岩演化过程划分为早期成礁与早期暴露、晚期成礁与次级暴露、埋藏压实与泥岩再造水改造阶段、两期成藏与地下水溶蚀4个阶段。根据沉积-成岩演化分析,预测了研究区储集类型空间分布。

Characteristics and genesis of reservoir spaces in Neocene reef reservoir of Liuhua Oilfield,Pearl River Mouth Basin

The reservoir of Liuhua oilfield,which belongs to Zhujiang Formation,is a typical Neocene platform-rim reef located on the margin of carbonate platform of Dongsha Massif in Pearl River Mouth Basin,South China Sea.There are 7 types of rocks,including crusty algal boundstone,twined algal-coral framestone,foraminifer and algal grainstone and rhodolite reef limestone.The reservoir spaces include 7 types of pores and 4 types of fractures.The main pores include primary intergranular pores,pores in algal frames,intragranular dissolved pores,cavity pores and intercrystalline micropores.The main fractures include dissolution fractures,interlayer fractures in crusty algal boundstone,and stylolite dissolved fractures.The reservoirs are classified into four types,including pore-cavern-fracture type,pore type,fracture-pore-cavern type and fracture type.Crusty algal boundstone belongs to pore-fracture type reservoir.Mieritic grainstone and rhodolite reef limestone are pore type.Coral framestone belongs to fracture-pore-cavern type.Fracture type includes sparry grainstone and relatively heavily cemented algal boundstone.Sedimentary microfacies and diagenesis control the distribution of different types of reservoir.Multiple exposures during the formation of reef have great influence on the reservoir.The sedimentary-diagenetic evolution of reef reservoir can be divided into four periods,including early reef formation and early exposure period,late reef formation and minor exposure period,reformation period during the early burial,two stages of reservoiring and groundwater dissolution periods.The spatial distribution of reservoir types are predicted according to the sedimentary-diagenetic evolution.