鄂尔多斯盆地七里村油田长7段致密储层孔隙结构特征及流体可动性

Pore structure characteristics and fluid mobility of tight reservoir in Chang7 Member of Qilicun Oilfield in Ordos Basin

孔隙结构和流体可动性是当前致密储层研究的重点和难点。以铸体薄片、扫描电镜、高压压汞和核磁共振等实验方法为基础,结合岩心特征等对鄂尔多斯盆地七里村油田长7段致密储层孔隙结构特征及流体可动性进行研究,为该区进一步勘探开发提供参考依据。研究结果表明:七里村油田长7段储层岩性为长石砂岩,储集空间类型主要是残余粒间孔与溶蚀孔,平均孔隙度为6.4%,平均渗透率为0.43×10^(-3)μm^(2)。研究区储层非均质性较强,孔喉结构参数和可动流体参数分布范围广,最大进汞饱和度和退汞效率都偏低,排驱压力较大,孔喉细小且连通性较差。核磁共振实验T_( 2)谱分布均呈左高右低的“双峰”形态,反映了研究区储层以小孔隙为主,可动流体饱和度较低,平均可动流体饱和度为23.39%,储层岩石孔隙结构复杂,储层物性、微观孔隙结构特征和黏土矿物含量都是储层流体可动性的重要影响因素。根据高压压汞曲线特征,将研究区储层孔隙结构划为Ⅰ类、Ⅱ类和Ⅲ类,不同类型孔隙结构的孔喉结构特征和可动流体含量及分布具有明显区别。

Pore structure and fluid mobility are the key points and difficulties in studying tight reservoirs.Based on experimental methods such as casting thin sections,scanning electron microscopy,high-pressure mercury injection,and nuclear magnetic resonance,this study combined core characteristics to study the pore structure characteristics and fluid mobility of tight reservoir in Chang7 Member of Qilicun Oilfield in Ordos Basin,providing a reference basis for further exploration and development in the area.The research results show that the reservoir lithology of Chang7 Member of Qilicun Oilfield is feldspar sandstone,and the primary reservoir space types are residual intergranular pores and solution pores,with an average porosity of 6.4%and an average permeability of 0.43×10^(-3)μm ^(2).The reservoir in the study area has strong heterogeneity,wide distribution of pore throat structure and movable fluid parameters,low maximum mercury injection saturation and mercury ejection efficiency,large displacement pressure,small pore throat,and poor connectivity.The distribution of the NMR T_( 2) spectrum experiment shows a bimodal type pattern with high left and low right,reflecting that the reservoir in the study area mainly comprises small pores,and the movable fluid saturation is low,averaging 23.39%.The reservoir pore structure is complex,and the reservoir’s physical properties,micropore structure characteristics,and clay mineral content are essential factors affecting the mobility of the reservoir fluid.According to the characteristics of the high-pressure mercury injection curve,the pore structure of the reservoir in the study area could be classified into class I,class II and class III,and the pore throat structure characteristics and movable fluid content and distribution of different types of pore structures have significant differences.