鄂尔多斯盆地东北部下石盒子组致密砂岩储层特征及主控因素

为揭示鄂尔多斯盆地东北部下二叠统下石盒子组致密砂岩储层的发育规律及主控因素，采用岩心观察、粒度分析、砂岩薄片鉴定、扫描电镜、毛细管压力分析、X衍射、有机质成熟度和包裹体测温等手段，研究了储层的岩石学特征、孔喉结构和物性特征。结果表明：该区储层主要以中-粗粒岩屑石英砂岩为主，岩屑砂岩和石英砂岩次之；储集空间类型包括剩余原生粒间孔、剩余原生粒间微孔、粒间溶孔、粒内溶孔和微裂缝，次生孔隙是储集空间的主体；喉道类型以片状型、缩颈型、管状喉道型与粒间隙喉道型为主；储层的平均孔隙度为6.07％，主体介于3.0%～10.0%之间，渗透率平均值为0. 093 mＤ，80%的值介于0.001～0.4 mＤ之间，属于以中、小孔-细、微喉组合为特征的致密砂岩储层。在此基础上，综合分析了致密储层与沉积、成岩作用的关系。结论认为：浅水三角洲砂岩是这些致密砂岩储层的物质基础；压实作用和胶结作用导致储层致密化；中成岩阶段有机酸对砂岩中不稳定矿物以及碳酸盐胶结物的溶解作用是储层形成的关键。

Features and main controlling factors of tight sandstone reservoirs in the Lower Shihezi Formation in the northeastern Ordos Basin

Aiming at revealing the development patterns and main controlling factors of tight sandstone reservoirs in the Shihezi Formation in the northeastern Ordos Basin, this paper studies the petrological features, pore throat structures and poroperm characteristics of the reservoirs through core observation, grain size analysis, thin section analysis, SEM, capillary pressure analysis, X ray diffraction, organic matter maturity and inclusion temperature measurement. Reservoir lithologies are dominated by medium to coarse grained lithic quartzite, followed by lithic sandstone and quartzite. The types of reservoir space include relic primary intergranular pore, relic primary intergranular micro pore, intergranular solution pore, intragranular solution pore and micro fracture, with secondary pores being the major reservoir space. The pore throats are mainly of lamellar throat, necking throat, tube like throat and intergranular slot type throat. The average porosity is 6.07%, with the bulk in the range of 3.0 10.0%. The permeability averages at 0.093 mＤ, with 80% of the samples in the range of 0.001~ 0.4 mＤ. The reservoir belongs to tight sand with medium, small, and micro pore throat combinations. The relationship between tight sand reservoirs and sedimentation and diagenesis is also discussed. Sandstones of shallow water delta facies are the material base for the formation of these tight reservoirs. Compaction and cementation are the main causes of tightness. Dissolution of the unstable minerals and carbonate cements in the sandstone by organic acid during the medium diagenetic stage is the key to improving the poroperm characteristics of the reservoirs.