蜀南低陡构造区须家河组储层砂岩致密化成因机制分析

Densification mechanism analysis of sandstone densification within Xujiahe formation in low-steep structure in southern Sichuan basin

为有效探寻并预测致密砂岩中"甜点"储层发育有利区域,采用铸体薄片鉴定、扫描电镜观察,结合物性测试资料、流体包裹体均一温度进行综合分析.结果表明,蜀南低陡构造区须家河组T3x4、T3x6为典型的致密低渗透气藏,储层砂体经历的成岩演化过程可分为以压实和石英次生加大为主的成岩序列、以绿泥石环边为主的成岩序列和以早期方解石胶结为主的3种演化路径.分析砂岩致密化成因机制表明:沉积作用是决定储层砂体物性的先天因素,压实作用是使储层致密的主要原因;成岩作用过程中的石英次生加大造成储层质量的致命性破坏,溶蚀程度低是储层砂岩致密的另一个重要原因;储层砂岩致密化时间发生在烃类充注前,石英次生加大边中发育的盐水包体均一温度分布在82.5~125.1℃之间,集中分布在100~120℃之间,推算储层砂岩致密化深度介于1 725~2 864m之间,致密化过程发生在燕山构造活动期间,储层砂岩致密化时间为1.5×108 a左右,致密化过程可划分为准同生期—早成岩A期的原生孔隙的迅速破坏阶段、早成岩A期—早成岩B期的机械压实阶段、早成岩B期—中成岩A期的胶结阶段等.该研究为在研究区须家河组进行"甜点"储层预测提供可靠的地质依据.

For the effective searching and predicting development areas of 'sweet spot' reservoir in the tight sandstone,using the cast thin section identification,scanning electron microscopy observation,combining the test data of physical properties with fluid inclusion homogenization temperature for comprehensive analysis,T_3x^4、T_3x^6 is a typical density low permeability gas reservoir within Xujiahe formation in low-steep structure of Shunan area.Diagenetic evolution of the reservoir sand body can be divided into three evolution paths:diagenetic sequences mainly with the compaction and secondary quartz overgrowth,diagenetic sequences mainly with chlorite rim and predominantly early calcite cementations furthermore analysis of the densification mechanism of sandbody.The results show that sedimentation is the congenital factor to physical property of sand reservoir.Compaction is the key factor for reservoir densification.Secondary quartz overgrowth could destroy the quality of reservoir.Lower dissolution degree is another key factor for reservoir densification;and the time of reservoir densification is before the hydrocarbons filling.The homogenization temperature of saline fluid inclusions distributed between82.5~125.1 ℃,concentrated distribution between 100.0 ℃~120.0 ℃,thus the prediction of densification depth is between 1 725~2 864 m,secondary quartz overgrowth,thus the densification process occurred during Yanshan tectonic activity.When the buried depth continued to increase,the hydrocarbons began charging,thereby the continuing of water-rock reaction were suppressed.The results of this studying provide the reliable geological data for reservoir predicting of ' weet spot' in Xujiahe formation.