铀的地球化学特征及其测井响应在油气勘探中的应用

UGEOCHEMICAL CHARACTERISTICS AND THE APPLICATION OF U LOGGING RESPONSE TO OIL-GAS EXPLOBATION,NGI

铀是一种强放射性元素，同时又是一种地球化学性质非常活泼的元素，具有高度的成岩敏感性。由于变价的特点，铀对成岩过程中环境的氧化还原电位、温度、压力、还原作用、吸附作用、酸碱度等变化反应灵敏，极易发生迁移和沉淀，导致铀的局部富集和贫化。铀的地球化学行为决定了它在地层中有良好的可动性，因而是一种有用的示踪元素，可以用来追索沉积体系演化过程中发生的许多重要地质事件。文章概述了铀在表生作用带的地球化学行为、分布状况和迁移富集规律，指出在沉积阶段沉积物中吸附的铀量很少，成岩作用才是使铀富集的根本原因；并以铀测井资料在四川盆地的应用为主，简述了在油气勘探开发中铀在识别岩性和研究生油层、储集层、构造断裂、沉积环境、成岩环境、地下水、古气候等方面的应用。

Uranium, with strong radioactivity, is of very vivacious geochemical characters and high diagenetic sensitivity. Because of it with shift valency, uranium is sensitive to the changes of environmental redox potential, pressure, reduction, adsorption, pH etc, in diagenetic course and is very easy of migration and precipitation to lead to its partial enrichment or poorness. The geochemical behaviors of uranium determine it has good moveability in formation. As and available trace element, uranium can be used to recollect the important geological events happened in the evolution course of depositional system. The geochemical behaviors, distributive situation, migration and enrichmet laws of uranium are generally described. It is pointed out that the quantity of uranium absorbed in depositional substance at depositional stage is very small and the basic cause of uranium enrichment is diagenesis. The applicaations of uranium to the aspects of identifying lithology and reserching oil source bed, reservoir, structral fracture, depositional environment, digenetic environment, groudwater and palaeoclimate are also generally described by the use of uranium logging data in Sichuan Basin.