碳酸盐岩核磁共振实验研究现状

Research status of nuclear magnetic resonance experiment in carbonate rock

随着海相碳酸盐岩油气田的大规模开发,对碳酸盐岩储层的评价日益受到重视。低磁场核磁共振(NMR)岩心分析技术是近20年来在我国新兴起的快速测量岩石物性参数的一种新技术,被广泛应用于储层评价及流体识别。针对NMR当前应用现状,文中就碳酸盐岩中存在的大、小孔喉"扩散耦合"、T_2截止值的准确求取以及温度对NMR响应特征的影响3个问题,总结了国内外相关学者的研究成果。"扩散耦合"在各类岩石中都可能存在,只不过是在碳酸盐岩中较为突出罢了;碳酸盐岩的T_2截止值普遍比砂岩高且变化较大,这一方面说明碳酸盐岩的非均质性较强,另一方面也可能与碳酸盐岩的"扩散耦合"相关;而温度对碳酸盐岩NMR响应特征的影响,则因碳酸盐岩的矿物成分、孔隙类型、流体性质而异。

Along with the large-scale development of marine carbonate oil and gas fields, the evaluation of carbonate reservoir is becoming increasingly important. Low field nuclear magnetic resonance（NMR） core analysis, a technology introduced into China just20 years ago, has been used ever since for rapidly measuring petrophysical parameters. It has been widely applied to reservoir fluid identification and reservoir evaluation. However, the application of NMR in carbonate reservoir still has some problems at present.This paper reviews academic research results in China and abroad concerning the following three issues： big and small pores ′ ＂diffusional coupling＂ in carbonate rocks, the accurate calculation of T2 cutoff value of carbonate rocks, and the influence of temperature on the carbonate NMR response characteristics. On this basis, it presents three findings： first, ＂diffusional coupling＂ exists in all kinds of rocks though it is more apparent in carbonate rocks than in other kinds of rocks; second, as the T2 cutoff value of carbonate rocks is generally higher than that of sandstone and also fluctuates within a broader range, it follows that carbonate rocks are highly heterogeneous, and that the T2 cutoff value may be associated with the ＂diffusional coupling＂ in the carbonate rocks; third, the influence of temperature on the carbonate NMR response characteristics varies with different mineral compositions, pore types and fluid properties.