川中侏罗系凉高山组微观孔隙结构特征及影响因素

Characteristics and Influencing Factors of Micropore Structures in Jurassic Lianggaoshan Formation in Central Sichuan Basin

根据岩心描述、薄片观察,并利用扫描电子显微镜、微米CT扫描成像、高压压汞、核磁共振等手段,对四川盆地凉高山组致密油储集层孔隙特征及其影响因素进行深入研究,认为凉高山组为一套退积-强进积旋回,主要发育石英砂岩类,孔隙度为1.0%~5.0%,渗透率基本上都低于1.0×10-3μm2,物性差。孔隙类型以粒内溶孔为主,粒间和构造缝发育次之,喉道主要为片状、管状。通过毛细管压力曲线将孔隙结构划分为4种类型,并应用J函数和沃尔公式计算得出Ⅰ类孔隙最小流动孔喉半径为75 nm。通过CT扫描切片技术发现孔隙分布状态主要为孤立状和连线状。强烈的压实作用使大量原生孔隙损失,孔隙中各种流体离子的半渗透膜效应引起碳酸岩盐和黏土矿物胶结使孔隙度进一步变差,酸性流体使得岩石发生溶蚀作用,发育粒内溶孔和粒间溶蚀扩大孔,改善了储集层的渗透性;CT扫描和核磁共振发现破裂作用形成的微裂缝能极大提高储集层的渗透率。

The characteristics and influencing factors of the pore structures in the Lianggaoshan Formation,Sichan Basin tight sandstone are investigated through core description,thin section observation,SEM,CT,high-pressure mercury injection and NMR.The results show that the Liangshan Formation is a retrograding-strongly prograding cycle;quartz sandstone is developed with porosity ranging from 1.0%to 5.0%,and permeability lower than 1.0×10^-3μm^2;pores are almost intragranular dissolved,followed by intergranular and structural fractures,and throats is almost lamellar and tubular.The pore structures are divided into 4 types according capillary pressure curves,and the minimum flowing radius of the Class I pores is 75 nm estimated by the J function and the Wall formula.The pore distribution is mainly isolated and connected according to CT data.Strong compaction results in the loss of most primary pores.The semi-permeable membrane effect of various fluid ions in pores causes carbonate and clay minerals to cement and further decrease the porosity.Dissolution by acidic fluid induces intragranular and intergranular pores,and improves the permeability.CT and NMR show micro-fractures also greatly improve the permeability.