惠州凹陷环惠州26洼古近系储层条件及对油气成藏的影响

Paleogene reservoir conditions around Huizhou 26 sag in Huizhou Depression and their influence on hydrocarbon accumulation

珠江口盆地惠州凹陷是一个已经探明的富油凹陷,其主力烃源岩为古近系恩平组和文昌组2套地层。为了进一步研究惠州凹陷环26洼古近系储层条件及其对油气成藏产生的影响,选择了HZ-A、HZ-B、HZ-C和HZ-D共4个构造,以HZ-A和HZ-B构造为主,利用储集砂岩的岩石成分、沉积相、孔隙度、渗透率、薄片鉴定等资料等,对研究区储层宏观特征和微观特征做出了较为完整的分析,并结合储层流体包裹体数据及埋藏史图做出HZ-A和HZ-B构造的古近系成岩-成储-成藏耦合关系图,以示储层条件及其对油气成藏的影响,可较为直观的反映及对比其成岩、成储、成藏过程。研究结果表明,4个构造文昌组沉积相以发育扇三角洲、滨浅湖、中深湖、近岸水下扇为主,恩平组则以辫状河三角洲和扇三角洲为主。HZ-A构造恩平组以长石类砂岩为主、文昌组以长石类和岩屑类砂岩为主,HZ-B构造恩平组以石英类砂岩为主、文昌组以石英类和岩屑类砂岩为主;恩平、文昌组均大量发育特低-低孔、特低-低渗储层,发育少量中孔-中渗储层。研究区主要成岩作用包括压实、溶解、石英加大、胶结、凝灰质蚀变等作用,但各构造成岩作用强度各有不同。通过综合分析发现,良好储集层的发育与适度的成岩演化是油气成藏的必备条件,同时也为油气提供了有效的横向运移通道,这是油气聚集的前提条件,并且丰富了油气输导类型,使油气更容易聚集成藏。

The main source rocks of the Huizhou oil-rich depression in the Pearl River Estuary Basin are composed of Paleogene Enping Formation and Wenchang Formation respectively.In this paper,four structures,namely HZ-A,HZ-B,HZ-C and HZ-D,are selected in Huizhou Depression,with the former 2 structures as the main research targets.The macro and micro characteristics of the reservoir in the study area are analyzed completely by using the data such as rock composition,sedimentary facies,porosity,permeability and thin section identification of the reservoir sandstone.Combined with reservoir fluid inclusion data and burial history map,the coupling relationship diagram of Paleogene diagenesis,hydrocarbon accumulation and reservoir formation of HZ-A and HZ-B structures is made to reveal reservoir conditions and their influence on oil and gas accumulation,and to compare the process of rock formation,hydrocarbon accumulation and reservoir formation.The results show that among the four structures in Huizhou Depression,the sedimentary facies of Wenchang Formation is dominated by fan delta,shallow shore lake,medium deep lake and near-shore underwater fan,while that of Enping Formation is dominated by braided river delta and fan delta.In the HZ-A structure,the Enping Formation is mainly composed of feldspathic sandstone and the Wenchang Formation is mainly composed of feldspathic and lithic sandstone,while in the HZ-B structure,the Enping Formation is dominated by quartz sandstone and the Wenchang Formation is dominated by quartz and lithic sandstone.Enping Formation and Wenchang Formation both develop a large number of ultra low-low porosity and ultra low-low permeability reservoirs,with a small number of medium-porosity and medium-permeability reservoirs.The main diagenetic processes in the study area include compaction,dissolution,quartz enlargement,cementation,tuffaceous alteration,etc.,with different diagenetic intensity in each structure.Comprehensive analysis indicates that good reservoir development and moderate diagenetic evolution are the necessary conditions for oil and gas accumulation,which enrich oil and gas transport types,provide effective lateral migration channels for oil and gas,and make oil and gas accumulation easier.