Lower Limit of Physical Properties of Filling Materials in Tight Reservoirs of the Chang 7 Member,Triassic Yanchang Formation,Ordos Basin,and Their Controlling Factors
Recently,significant breakthroughs have been achieved in exploring tight reservoirs within the Chang 7 Member of the Yanchang Formation in the Ordos Basin.The lower limit of reservoir filling material properties is crucial for assessing the potential for tight oil exploration and development in this area.In this study,we ana-lyzed the lower limit of physical properties for filling materials in tight reservoirs across different regions and lay-ers using pore penetration analysis,oil saturation measurement,and high-pressure mercury injection.Addition-ally,we examined the lower limit of physical properties for filling materials in tight reservoirs across different regions and layers using the physical oil test method,empirical statistical analysis,and pore throat radius meth-od.We also explored the controlling factors and their influence on the oil and gas enrichment.The results indi-cate that in the Longdong-Jiyuan area,dense sandstone is primarily composed of quartz,with an average reser-voir pore penetration of 8.17％and 0.15 × 10-3µm2;in contrast,the dense sandstone in north Shaanxi is pre-dominantly feldspar,exhibiting an averages reservoir pore penetration of 8.20％and 0.21 × 10-3μm2.In the Longdong-Jiyuan area,the lower limit of physical properties for dense reservoirs in the Chang 71 submember is 4.93％and 0.034 × 10-3 μm2,while in the Chang 72 submember,it is 4.36％and 0.027 × 10-3 μm2.In north Shaaxi,the lower limit of the physical properties for dense reservoirs in the Chang 7,submember is 5.90％and 0.048 × 10-3 µm2,while in the Chang 72 submember,it is 5.60％and 0.043 × 10-3 μm2.The lower limit of reservoir filling is influenced by three factors:the physical properties of the reservoir,the hydro-carbon generation capacity of source rocks,and the distance between the sources and reservoirs.The lower lim-it of reservoir filling is lower in the areas with favorable reservoir properties,high hydrocarbon generation capaci-ty of source rocks,and minimal distance between sources and reservoirs.For example,in the Longdong-Jiyuan area,where the thickness of hydrocarbon source rocks is greater than in north Shaanxi,the lower limit of reser-voir filling is lower.The lower limit of reservoir filling is lower in the Chang 72 submember,where the distance between sources and reservoirs is smaller compared to the Chang 7,submember.A lower limit of reservoir fill-ing is associated with higher oil saturation.For example,in the Longdong area,the lower limit of reservoir fill-ing is relatively low,the average oil saturation is 31.28％.In contrast,the average oil saturation innorth Shaanxi is 28.40％,which is significantly lower than in Longdong.Similarly,the oil saturation in the Chang 72 submember reservoir is higher compared to the Chang 7,submember reservoir.
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