基于核磁共振T_2谱集中度的低孔隙度低渗透率储层饱和度参数研究

歧口凹陷中深层低孔隙度低渗透率储层沉积环境和成岩作用的复杂性导致孔隙结构复杂,储层非均质性强,常规实验室得到的不同岩样的m、n值均存在明显差异,其中m变化范围为1.0~2.5,n变化范围为1~6,区域平均m、n值已经满足不了低孔隙度低渗透率储层饱和度评价。综合分析300余块次岩样的岩电参数发现,岩样m、n值受孔隙度、地层水电阻率、孔隙结构特征形态等因素共同制约。提出核磁共振T_2谱集中度概念反映微观孔隙结构分布形态,分不同地层水电阻率范围,建立利用核磁共振T_2谱集中度计算饱和度关键参数m、n的解释模型,获得连续的、反映储层物性变化的m、n值,有效提高了m、n参数计算准确性,m值相对误差降低到2.1%,n值相对误差降低到7.23%。将该研究成果应用于生产实践,取得了很好的效果。

Key Parameters of Water Saturation Based on Concentration of T2 Spectrum Distribution

The most critical factor for carrying out the quantity evaluation of the oil saturation is the rock-electro parameters:m and n.The traditional method to get the parameters of m and n is to use the relationship between formation factors and porosity and the relationship between water saturation and resistivity increasing ratio index to obtain the average value of parameter m and n in the region by carrying out experiments, which can meet the demand of the quantity oil saturation evaluation for the conventional homogeneous reservoir with good porosity.Unfortunately, the mid to deep formations in the Qikou sag are of low porosity and low permeability, due to the complexity of deposition system and diagenesis, the pore space structure becomes more complex and the formation inhomogeneity becomes stronger, so there are obvious differences between the parameters m and n from different core samples experiments, the parameter m ranges from 1 to 2 and n from 1 to 6, the average values of m and n in the region are not suitable for oil saturation evaluation of low porosity and low permeability reservoirs.According to the rock-electro parameters from the comprehensive analysis of 300 core samples, it can be found that the values of m and n are affected by porosity, formation water resistivity and pore space structure characteristics.An idea which is based on the concentration of NMR T2 spectrum distribution to show the microscopic pore space structure is provided.In terms of the ranges of the water resistivity, the interpretation models of the key parameters m and n are built in terms of the concentration of NMR T2 spectrum distribution, the parameters m and n which reflects the reservoir porosity and permeability of the reservoirs can be obtained continuously with depth.This method can effectively raise the accuracy of m and n, the relative error m drops to 2.1%, n to 7.23%.The researches have been put into practice and achieved good results.