塔东地区米兰1井寒武系白云岩成因及其对储层的影响

白云岩储层展布是塔里木盆地塔东地区深层白云岩油气藏勘探的关键问题。为认识塔里木盆地塔东低凸起米兰地区寒武系白云岩，选取典型井米兰1井，在岩心和镜下薄片观测的基础上，对各种类型的白云岩进行了稀土元素地球化学特征测试。结果表明，各类白云岩稀土元素含量均较低，且随着晶粒增大，总质量分数减小；不同类型白云岩的δEu异常显著不同，泥微晶、细晶、中晶和粗晶白云岩的δEu分别介于0.97~1.08，0.77~1.05，0.80~3.23，0.81~2.23；大部分样品δCe负异常，介于0.86~1.02。所有样品稀土元素PAAS配分模式分为3种类型，即δEu负异常型、δEu正异常型和δEu无异常型。在白云石化过程中，蒸发泵机制是米兰1井寒武系白云岩的基础成因，第一种白云岩后期还受到埋藏环境的影响，第二种后期还受到热液环境改造，第三种形成于回流渗透机制。白云岩储层的形成受多种条件的控制，其中有利的沉积环境是储层形成的先决条件，大规模白云石化是储层形成的基石，裂缝体系对储层有多重影响，而溶蚀作用是储层形成的关键。

Origin of Cambrian dolomite from Well Milan 1 in Tadong area and its significance to dolomite reservoirs

Knowing reservoir distribution pattern is key to the exploration of deep dolomite reservoirs in the eastern Tarim Basin.To understand the origin of the Cambrian dolomite in the Milan area of the Tadong low uplift, we measured the rare earth elements (REE) of dolomite of various types taken from a representative well Milan 1 for geochemical characterization based on core and thin section observations.The results show that the content of all REEs in various dolostones is low, and the total mass fraction decreases with the increase of grain size.There are obvious differences in δEu anomalies for dolostones of different types.The δEu anomaly values of silty-micritic, finely-crystalline, medium-crystalline and coarse-crystalline dolostones range between 0.97-1.08, 0.77-1.05, 0.80-3.23 and 0.81-2.23, respectively.Most of the samples have negative δCe anomaly values, ranging from 0.86 to 1.02.The results show that the PAAS-normalized pattern of REEs in all samples can be divided into three types:the negative, positive and normal types.An in-depth study on the dolomitization process demonstrates that the formation of the Cambrian dolomite is essentially caused by evaporation pump mechanism.In addition, the dolomite of the negative type was also under the impact of a burial environment at a later formation stage; the positive type was modified in a hydrothermal environment at a later stage; and the normal type was mainly formed under the effect of seepage reflux.In conclusion, the formation of dolomite reservoirs is conditioned by a variety of factors, including a favorable distribution of sedimentary facies as a prerequisite; large-scale dolomitization as the foundation; dissolution as the key, and the fracture systems as versatile influencers.