四川盆地九龙山构造须二段致密砂岩储层裂缝特征、形成时期与主控因素

Characteristics,timing and controlling factors of structural fractures in tight sandstones of the 2nd member of Xujiahe Formation in Jiulong Mountain structure,Sichuan Basin

四川盆地西北部须家河组二段致密砂岩储集性能受到不同期次构造裂缝控制,研究构造裂缝特征、期次以及控制因素将为有效评价与预测有利储层提供依据。根据露头、钻井岩心及薄片构造裂缝观察,划分构造裂缝切割关系,认为构造裂缝走向主要为北东向、北北西向、近东西向和南东东向,其中优势方位为北西-南东方向。利用不同切割关系裂缝充填物包裹体均一温度、ESR测年数据,结合岩石古应力值将研究区构造裂缝至少划分为4期:第一期构造裂缝形成于晚印支期,方解石呈紧挨裂缝壁充填,包裹体均一温度为84～120℃;第二期为晚燕山期,裂缝主要充填石英,均一温度为72～137℃;喜马拉雅早-中期是第三次破裂期,其裂缝充填石英,明显切割前两期裂缝,均一温度为153～179℃;喜马拉雅晚期是第四次破裂期,其形成的裂缝充填物为较粗大的方解石,少量白云石,均一温度高达165～190℃。其中印支晚期与喜马拉雅晚期构造活动最为强烈,裂缝发育。同时,研究区构造裂缝的发育和分布受构造应力和岩石自身物理参数共同控制,高孔隙度、细粒级、薄层的岩屑砂岩是形成构造裂缝的有利条件。

Physical properties of tight sands in the 2nd member of Xujiahe Formation in northwestern Sichuan Basin are controlled by structural fractures（SF）formed at different stages.The study on characteristics,timing and controlling factors of the structural fractures can provide useful information for reservoir evaluation and prediction.Identification of cutting relations of the SF on the basis of fracture observation on outcrops,cores and thin sections reveals that the SF can be grouped into NW-SE-trending,NE-trending,NNW-trending,near EW-trending and SEE-trending,of them NW-SE-trending is predominant.At least four stages of SF were identified based on the analysis of the fluid inclusion homogenization temperature of fillings in fractures with different cutting relation and ESR,as well as palaeo-stress data.The first stage is the Late Indosinian,and the SF formed at this stage feature in calcite filling and fluid inclusion homogenization temperature（FIHT）of 84-120 ℃.The second stage is the Late Yanshanian,and the SF formed at this stage are characterized by quartz filling and FIHT of 72-137 ℃.The third stage is the Early-middle Himalayan Period and the SF formed at this stage feature in quartz filling,cutting relations with the SF of previous two stags,and FIHT of 153-179 ℃.The fourth stage is the Late Himalayan Period,and the SF formed in this stage are characterized by coarser calcite fillings with some dolomites and FIHT of 165-190 ℃.Because of the active tectonic movement during the Indosinian and Himalayan Period,the SF are well developed.The formation and distribution of SF are jointly controlled by tectonic stress and the mechanical property of rocks.Lithic sandstone with high porosity,fine particle and thin layer are favorable for SF development.