陆丰凹陷文昌组低渗低阻储层特征及成因研究

Study on characteristics and genesis of low-permeability and low-resistivity reservoirs in Wenchang Formation of Lufeng sag

陆丰凹陷古近系深层发现大量低渗低阻储层,其孔渗关系复杂、流体性质识别困难,制约了勘探开发进程。以岩石学和物性资料为基础,结合沉积和成岩等多方面研究,对陆丰凹陷文昌组低渗低阻储层的特征和成因开展研究。文昌组储层以岩屑石英砂岩为主,储集空间以次生孔隙为主,由中-小孔和细喉道组成,同类粒度样品的孔渗相关性较好,根据毛细管曲线形态可分为高进汞饱和度、低排驱压力,中等进汞饱和度、中等排驱压力和中进汞饱和度、中-高排驱压力三类。沉积环境以近源辫状河三角洲水下分流河道为主,砂岩成分成熟度和结构成熟度较低,储层质量受沉积条件控制;压实作用造成原生孔隙大量减少,胶结物充填粒间导致物性进一步变差,是造成低孔、低渗的主因。研究结果表明,储层岩性变化快,孔隙结构复杂,孤立孔隙多和联通性差导致束缚水含量较高,以及地层水矿化度高的共同影响,是研究区低对比度储层的发育机理。该认识对本区后续勘探开发作业具有一定的指导作用。

A large number of low-permeability and low-resistivity reservoirs have been found in the deep Paleogene formation of Lufeng sag.The complicated relationship between porosity and permeability and the difficulty in identifying fluid properties restricted the exploration and development process.Based on petrology and physical property data,and combined with sedimentary and diagenetic studies,the characteristics and genesis of low-permeability and low-resistivity reservoirs in Wenchang Formation of Lufeng sag were studied.The reservoirs of Wenchang Formation are dominated by lithic quartzose sandstone,the storage spaces are mainly secondary pores,composed of medium-small pores and fine throats,the porosity-permeability correlation of samples of the same particle size is good.According to the capillary curve shape,it can be divided into three categories:high mercury saturation&low displacement pressure,medium mercury saturation&medium displacement pressure,and medium mercury saturation&medium-high displacement pressure.The sedimentary environment was dominated by near-source braided river delta underwater distributary channel,the compositional maturity and textural maturity of the sandstone are low,and the reservoir quality is controlled by the sedimentary conditions.The major cause of the low-porosity and low-permeability is that the primary pores are greatly reduced due to compaction,and the physical properties are further deteriorated due to cement filling the pores between particles.The results show that the development mechanism of low-contrast reservoirs in the study area is the combination of rapid lithology change,complex pore structure,high bound water content due to more isolated pores and poor connectivity,and high salinity of formation water.This understanding has a certain guiding effect on the follow-up exploration and development in this area.