柴达木盆地南翼山油田新近系油砂山组低渗微裂缝储集层特征及成因分析

通过岩心观察、薄片鉴定并借助X衍射全岩矿物分析，对柴达木盆地南翼山油田新近系油砂山组储集层特征进行分析。该区岩石中泥质含量高，岩性复杂，可划分为泥岩、碳酸盐岩、砂岩和混积岩4种类型。储集层中发育粒间孔、溶蚀孔、微孔隙和微裂缝等，形成了具有双重孔隙介质的储集空间特征。微裂缝是该区主要渗流通道，而微孔隙是主要储集空间，储集层物性总体较差。该区微裂缝类型包括构造缝、溶蚀缝和成岩缝。储集层岩石纹层发育，砂质纹层和泥灰质纹层交互出现，沉积和成岩作用过程中岩石受力不均衡、碳酸盐矿物的溶解以及泥岩收缩是形成微裂缝的主要原因。该区储集层物性受压实作用明显变差，溶蚀和胶结作用同时存在，对储集层物性影响较大。储集层岩石毛管压力曲线由近似垂直的斜线段和近似水平的曲线段两部分组成，中间存在较为明显的拐折点。斜线段反映了微裂缝特征，近似水平曲线反映了微孔隙特征。利用毛管压力曲线求取的排驱压力和平均孔喉半径无法真实地表述此类微裂缝储集层的孔隙结构特征，提出了有效孔喉半径概念，可以合理表述该区微裂缝储集层孔隙结构特征。

Analysis of characteristics of low-permeable reservoir with micro-fracture and their origins of the Neogene Youshashan Formation in Nanyishan Oilfield, Qaidam Basin

The reservoir characteristics of the Youshashan Formation of the Neogene in Nanyishan Oilfield were analyzed according to core observation,thin section identification and X-ray diffraction.The lithology of the reservoir can be classified as mudstone,carbonate rocks,sandstone and hunji rock.The clay content of the rock is high and the reservoir properties are complex.Intergranular pores,dissolution pores,micro-pores and micro-fractures are developed,so the reservoir has the characteristics of dual porous media.In general,the physical properties of the Nanyishan reservoir are poor.It is pointed out that the micro-fractures play an important role in the flowing of formation fluids,but micro-pores contribute little to the flowing.The micro-fractures in the reservoir include tectonic micro-fracture,dissolution micro-fracture,and diagenetic micro-fracture.Sandy lamination and argillic or marlaceous lamination are developed alternately in the rock.The unbalanced force,dissolution and shrinkage of reservoir rock during sedimentation and diagenesis resulted in the formation of micro-fractures which improve physical properties of the reservoir.However,compaction and cementation happened simultaneously,which destruct the reservoir properties.The mercury injection curves of the reservoir are composed of two parts: Inclined upward curve and approximately horizontal curve.The tilted curve represents the micro-fracture,and nearly horizontal curve represents micro-pores.Parameters such as threshold pressure and mean pore radius cannot be used to evaluate the reservoir correctly.So,a parameter of effective pore radius is put forward in this paper and can be applied to evaluate the reservoir properly.