鄂尔多斯盆地延安地区山西组山2段储层可动流体赋存影响因素分析

Influence Factors of the Movable Fluid in the Shan 2 Reservoirs of the Shanxi Formation in the Yan an Area,Ordos Basin

山2段是鄂尔多斯盆地延安地区致密砂岩气生产的重要层段,目前对其流体赋存规律认识明显不足。因此在铸体薄片、扫描电镜、X射线衍射、高压压汞、恒速压汞、核磁共振测试的基础上,分析该储层可动流体的赋存特征及其影响因素。结果表明:山2储层主要为岩屑石英砂岩和岩屑砂岩,溶蚀孔和晶间孔为主要储集空间,粒间溶孔显著发育。山2储层可动流体饱和度为34.74%~91.83%,平均为69.94%,T 2谱多为双峰态,呈左低右高型。储层孔隙度、渗透率、孔隙类型、孔喉特征及胶结物影响可动流体饱和度。孔隙为可动流体提供主要空间,平均孔隙半径越大,平均喉道半径越大,孔喉比越小,可动流体饱和度越高。硅质含量越高,粒间孔保存越好,可动流体饱和度越高。铁方解石含量越高,孔隙破坏越明显,可动流体饱和越低。高岭石含量较高,长石溶孔及晶间孔发育较好,有利于流体流动,可动流体饱和度也较高。

The Shan 2 member sandstone of the Shanxi Formation hosts the major tight reservoirs in the Yan an area,but the understanding remains poor now on the occurrence law of movable fluid in the rock.To solve this problem,based on casting thin-section,SEM,X-ray diffraction,high pressure mercury injection,constant rate mercury injection and nuclear magnetic resonance,this work analyzes the characteristics and influencing factors of the movable fluid in the reservoirs of this area.The results show that the Shan 2 reservoirs are hosted in lithic quartz sandstone and lithic sandstone,where dissolution pores and intercrystaline pores are the main reservoir space,especially intergranular dissolution pores.The movable fluid saturation of the reservoirs is 34.74%~91.83%,69.94%on average.The T 2 spectra are mostly of a bimodal state,with low left and high right.Porosity,permeability,pore type,pore throat characteristics and cement affect the movable fluid saturation.Pores are the main space for the movable fluid.The reservoirs with larger average pores and throat radius,and lower pore throat ratios have higher saturation of the movable fluid.The reservoirs with higher siliceous content usually have higher saturation of the movable fluid,because intergranular pores are well preserved in the sandstone.The reservoirs with higher content of ferruginous calcite have lower saturation of movable fluid.The reservoirs with higher content of kaolinite have higher movable fluid saturation because of development of dissolution pores and intergranular pores in feldspar.