Abstract:

Based on studies of fluids in formation and evolution of dolom ite reservoirs with REE in recent years and in combination with REE analyses of typical samples from the Sichuan and Tarim basins，fourmajor REE models are presented to identify the sources and behavior characteristics of fluids.（1）REE modelwith dolomites weakly altered by diagenetic fluids still showing seawater origin.It is characterized by lowwhole-rock gross REE content（generally<20μg/g），significant positive Ce anomaly，LREE enrichment，and relatively flat HREE distribution patterns;（2）Meteoric water leaching-percolation REE model.It features in whole-rock REE content being lower than thatofnormal dolom ite，positive Ce anomaly significantly lowering and even turning into negative Ce anomaly，and calcite veins ofmeteoric water leaching origin being the lowest in REE content;（3）Diagenetic fluid-hydrocarbon fluids REE model.It is characterized by slightly lowering whole-rock REE content but sim ilar distribution patterns as seawater.The associated dolom ite overgrowth has relatively higherREE content and Ce SWN value.Calcite veins ofdiagenetic fluid origin have significanthigherREE content and Ce SWN value than thatofhost rock.However both of them show the characteristic of seawater origin;（4）Hydrothermal alteration model.It features in lowerREE content，positive Eu anomaly and undulating REE distribution patterns.

Key words: discrim inative model, REE, fluid action, diagenetic evolution, dolomite reservoir