四川元坝地区大安寨段陆相细粒沉积岩储层物性特征及有利储集层研究

Study on Physical Properties and Favorable Reservoirs of Terrestrial Pulveryte Reservoirs in Da'anzhai Member,Yuanba Area,Sichuan

四川盆地元坝地区大安寨段陆相细粒沉积岩不同于盆地内其他地区,储层的物性差异较大,需对该区域目的层段细粒沉积岩储层物性特征开展研究。综合利用薄片观察、氦气法测孔渗、低温氮气吸附、扫描电镜及FIB等方法,对研究区岩石的物性特征、储集空间、孔隙结构和渗透性进行分析研究。结果表明:研究区细粒沉积岩储层储集空间类型分为孔隙和裂缝两大类,包括有机质孔、粒间孔、溶蚀孔、晶间孔、黏土矿物间微孔和构造缝、页理缝、成岩收缩缝;平均孔隙度为3.35%,平均渗透率为1.54 mD,属于特低孔低渗的孔缝型储层;细粒岩储层以微孔和介孔为主,孔径主要为3~7 nm;大二亚段富有机质页岩和介壳页岩是最有利的储集岩性,大安寨段下部和中部的富有机质细粒岩段为有利储集层段。储层特征分析有助于揭示大安寨段陆相特低孔低渗致密储层形成机理,也可为该类储层成因解剖与分布规律预测提供支撑和借鉴。

The terrestrial pulveryte of Da'anzhai Member in Yuanba Area of Sichuan Basin is different from that in other areas in the Basin,and the physical properties of the reservoirs are quite different,so it is necessary to study the physical properties of the pulveryte reservoirs in the target member in this area.The physical properties,reservoir space,pore structure and permeability of rocks in the study area were analyzed by means of microscopical observation,porosity and permeability measurement with helium,low-temperature nitrogen adsorption,scanning electron microscope,FIB,etc.The results showed that the pulveryte reservoir space type in the study area was classified as pore and fracture,including organic matter pore,intergranular pore,dissolved pore,intercrystalline pore and micropore among clay minerals,as well as tectonic fracture,shale bedding fracture and diagenetic shrinkage fracture;the average porosity was 3.35% and the average permeability was 1.54 mD,so this reservoir was a pore-fracture reservoir with ultra-low porosity and low permeability;the pulveryte reservoir was dominated by micropores and mesopores with a size of mainly 3 to 7 nm;the organic-rich shale and shell shale were the most favorable reservoir lithology in the second sub-member,and the organic-rich pulveryte section in the lower and middle layers of the Da'anzhai Member was the favorable reservoir interval.The analysis of reservoir characteristics is helpful to discover the formation mechanism of terrestrial tight reservoirs with ultra-low porosity and low permeability in the Da'anzhai Member,and also provides support and reference for the genesis analysis and of distribution rule prediction of such reservoirs.