海拉尔盆地碎屑岩储层束缚水饱和度的确定

核磁测井资料确定束缚水饱和度主要是采用T2固定截止值法.随着对复杂岩性储层的勘探,近年来,在固定T2截止值方法基础上又发展了锥形T2截止值法、薄膜模型以及频谱模型.对于岩性多变、孔隙结构复杂的碎屑岩储层,常规测井方法和以T2截止值为基础的核磁测井方法确定的束缚水饱和度都难以满足测井评价的精度要求,这时需要考虑薄膜模型和频谱模型方法.这两种模型认为各种尺寸的孔隙中均含有束缚水,只是不同尺寸孔隙束缚水含量不一样.在对海拉尔盆地岩性多变、孔隙结构复杂的碎屑岩储层的实践中,对回波串数据作多指数反演拟合时采用了2的幂次方方式布点,相应地得到了核磁测井T2谱,并从中选取了9个孔隙组分,将其与反映粘土含量的中子-密度孔隙度差值结合,采用回归的方法得到了束缚水饱和度的计算公式.回归公式在海拉尔盆地取得了较好的应用效果,尤其是贝尔凹陷,预测效果提高了将近1倍,计算的束缚水饱和度与岩心分析束缚水饱和度相比,平均相对误差从15.1%减小到8.7%.

Determination of the Irreducible Water Saturation of Clastic Reservoirs in Hailaer Basin

Constant T2cuttoff was mainly used in the determination of irreducible water saturation with NMR log information before.Some new methods,such as taper T2cuttoff,film model and frequency model,have been developed recently.As for the clastic reservoirs with variable lithology and complicated pore structure,the methods using conventional log information or using NMR log information based on T2cuttoff all can't obtain the irreducible water saturation meeting the require of log evaluation and interpretation.In this instance,film model or frequency model could be used.Both models suggested that irreducible water was existed in all pore size,and the percentage of irreducible water varies with the size of pore.Bur there has not been a criteria for that of what the size intervals of pore should be used in the determination of irreducible water saturation with the two models in practical application.Some attempts about the problem had been done upon the clastic reservoirs with variable lithology and complicated pore structure in Hailaer Basin.Firstly the distribution of power of 2 is used in multi-exponential inversion of NMR echo trains to obtain the T2 spectrum.Then nine pore volumes selected from T2 spectrum of NMR,together with the difference of neutron and density porosity reflecting the volume of clay,were used to calculate the irreducible water saturation with regression.Preferable results had been achieved in its application of clastic reservoirs of Hailaer Basin,the irreducible water saturation calculated had been improved compared to the core analysis data.Especially in Beier area,the average relative error between the irreducible water saturation predicted and the core analysis data is reduced from 15.1% to 8.7%.