The Identification Of Low Resistivity Layer Of N₂¹ Reservoir In Wu Nan Oil Field

Low resistivity oil layer is the layer which resistivity similar to the adjacent water layer or slightly higher than it. Due to the complex formation of the low resistivity reservoir, conventional logging tools and interpretation methods are limited. It is often interpret the low resistivity reservoir as a water layer and be left out. So, establishing low resistivity reservoir identification methods that not only suit for WuNan oil filed, but also suitable for other oil fields, will bring positive effects in improving the interpretation accuracy of low resistivity reservoirs and the level of reservoir exploration.According to the characteristics of fine lithology, poor physical properties and the complex pore structure, we can analysis the relationship among the "four nature" of N21 reservoir by the integrated using of literature method, research method, reservoir sedimentology method, mathematical statistics method, regression analysis method and SVM method, on the base of regional geological characteristics. We can come to the conclusion that the lithology of the reservoir is mainly composed of siltstone group and fine sandstone, especially the siltstone group after the analysis of "four nature". On top of this, We can dug out the sensitive information of low resistivity oil layers from the matching relationship among lithology, physical property, oil content and electrical property. Then establish the well logging parameter interpretation model, Finding out high irreducible water saturation and high reservoir water salinity are the main reasons for the formation of low resistivity reservoirs, and what for the high irreducible water saturation are complex pore structure, adsorption of water on rock particles and adsorption of clay particles. On the basis of studying the mechanism of low resistance, I find AC-RILD, RD-RILD curves overlapping method, RILD-AC, RD/RILD-RILD, RILD-â–³SP intersection chart method, array induction logging method, the SVM classification method, oil saturation method to identify the low resistivity reservoir. It is better to use curves overlapping method and SVM classification method to classifiy the low resistivity reservoir where there is conflict. The curve overlapping method, array induction method, SVM classification method has wider application range, which can be used to less production data condition. When we have enough production data, we can also use intersection chart method and oil saturation method to classifiy the low resistivity reservoir. We use some production wells to verificate those methods above, finding out that those methods can identificate the low resistivity reservoir very well. We use those methods to acurately explained 337 wells in the studying area, adding 46 low resistivity oil wells and 75 low layers The result shows that the low resistivity reservoirs are mainly distributed in the 101 block which belongs to the lower structure. Low resistivity oil reservoir is mainly distributed in IV-4, IV-10, III-21 layers, a small amount of distribution in IV-16 layer.This study enriched the identification method of low resistivity oil layers, it can provide the reference meaning for oil and water identification for similar low resistance oil reservoir. Furthermore, the study of Wunan oilfield of oil-water layer again improved the development effect and economic benefit of Wunan Oilfield, in addition of laying the theoretical and technical basis of science for the scientific and reasonable development of Wunan oilfield. Therefore, it has great scientific significance and practical value to study this topic.