鄂尔多斯盆地陇东地区二叠系盒8下段致密砂岩储层特征

陇东地区是鄂尔多斯盆地上古生界天然气勘探的新区带,二叠系下石盒子组盒8_下段气层组是其主力产气层,该区沉积、储层和成藏等方面具有一定的复杂性,天然气勘探研究程度较低。结合测井资料、岩心观察、铸体薄片、物性等资料,对鄂尔多斯盆地西南地区二叠系下石盒子组盒8_下段储层的岩石学特征、物性特征、孔隙结构特征进行研究,探讨了影响储层储集性能的主要控制因素。研究结果显示:盒8_下段储层砂岩类型以石英砂岩及岩屑石英砂岩为主,长石砂岩含量少,属于距离物源较远的高能环境产物。成岩作用过程中,砂岩储层经历强烈压实和压溶作用,碎屑颗粒和岩屑相互嵌合,伴有不同程度石英再生长,原生粒间孔隙大量消失,孔隙类型以粒内孔和岩屑溶孔为主,孔隙大小以微孔—中孔型为主。储层物性受沉积相和成岩作用共同控制。沉积相在根本上控制着储层物性条件,砂体结构对储层产生重要影响,切割型单砂体储层物性相对较好,拼接式砂体储层物性次之,孤立型单砂体物性较差。压实是造成储层物性致密化的主要原因,胶结作用中水云母是造成储层致密化的首要因素,储层溶蚀程度较低,对改善储层质量效果有限。该研究成果可对陇东地区盒8_下段的进一步勘探、开发提供可靠的地质基础和科学依据。

Reservoir Characteristics of Permian Lower He 8 Member in Longdong Area,Ordos Basin

The Longdong area is a new natural gas exploration zone in the Upper Paleozoic Ordos Basin. The Permian Lower Shihezi Formation (lower He 8 gas member) is the main gas-producing layer. The local deposition, reservoir and accumulation are relatively complex, and the level of understanding in the natural gas exploration is relatively low. Combining logging data, core observation, thin-section, physical properties and other data, we investigated the petrological characteristics, physical properties, and pore structural characteristics of the lower He 8 reservoir of the Lower Shihezi Formation in the southwestern Ordos Basin, and we discuss the main controlling factors on the reservoir performance. The results show that the reservoir sandstones of the lower He 8 are dominated by quartz sandstone and lithic quartz sandstone. Arkose content is low, suggestive of a high-energy and distal-source environment. During diagenesis, sandstone reservoirs may have undergone intense compaction and pressure dissolution, and the clastic particles and lithic fragments are interlocked with each other, accompanied by different degrees of quartz regrowth, and the disappearance of large number of primary intergranular pores. The pore types include mainly micro-sized intragranular pores and rock chip-dissolved pores. The reservoir physical properties are controlled by both the sedimentary facies and diagenesis. Sedimentary facies fundamentally control the reservoir physical properties. The sand-body structure has an important impact on the reservoir physical properties. The physical properties of the cut-type single sand-body are relatively good, followed by the spliced sand-body, and then by isolated single sand-body. Compaction is the main reason for the densification of the layer physical properties. Hydromica is the primary factor for the densification of the reservoir due to cementation. The degree of reservoir dissolution is low and the improving effect on the reservoir quality is limited. Our results provide a reliable geological basis and scientific basis for the further exploration and development of the lower He 8 reservoir at Longdong.