基于实验分析的泥质砂岩T_2截止值确定方法研究

Research on T2 Cutoff-value Determination Method for Shaly Sand Based on Experiments

核磁共振T2截止值(T2,cutoff)的确定主要通过离心法和经验值法得到,在实际应用中具有极大的局限性。根据泥质砂岩的渗流特性和Coates-cutoff模型建立了泥质砂岩的T2,cutoff计算模型。核磁共振T2,cutoff与岩石的孔隙结构、渗流特征有关;泥质砂岩的T2,cutoff分布范围较大。通过对渗透率模型的对比分析,得到了T2,cutoff与阳离子交换容量QV的理论模型;泥质砂岩的T2,cutoff随着QV的增大而减小,但其减小幅度随着QV的增大而不断减小。研究表明,岩石的核磁共振T2,cutoff与阳离子交换容量QV呈幂函数的关系;可通过该模型进行T2,cutoff的精确计算,为T2,cutoff的计算方法提供了一个新的思路。在实际应用中需要考虑阳离子交换量如何准确计算的问题。

The determination of NMR T2 cutoff-value is one of the most important sections in laboratory analysis as well as in practical nuclear magnet resonance logging data analysis. And nowadays, most researchers usually adopt the centrifugation method or experienced value method to determine T2cutoff value. However, these two methods have great limitations in practical log- ging. Based on the seepage characteristics of shaly sand and Coates-cutoff model, established is T2 cutoff calculating model of dispersed shaly sand. The NMR T2,cutoff has relation with rock porous structure and seepage feature; Distribution range for the T2 cutoff of the shaly sand is wider. A theoretical model of T2,cutoff and Qv has been obtained from permeability model analyses. The T2,cutoff the shaly sand continuously decreases with the increases of Qv. The above result indicates that the T2 cutoff and Qv has a relationship of power function and the exactly T2 cutoff value can be predicted by this model, which has a significant meaning for extensively analysis of nuclear magnet resonance logging. How to calculate accuracy Qv should be considered in practical log ging.