Pore structure characteristics and fluid mobility of tight reservoir in Chang7 Member of Qilicun Oilfield in Ordos Basin
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 μm2.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 T2 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.
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