塔里木盆地塔河油田东南斜坡海西晚期奥陶系热液作用

Study on the Ordovician hydrothermal action at Late Hercynian in the southeast slope of Tahe Oilfield,Tarim Basin

塔里木盆地塔河地区在早二叠世末存在2种性质的岩浆活动,基性及中酸性岩浆,分别源自地幔和地壳,岩浆热液流体作为一种化学活动性物质在其运移过程中对奥陶系碳酸盐岩储层产生溶蚀改造。塔河东南斜坡奥陶系缝孔洞方解石包裹体均一温度达到247℃,盐度远大于奥陶纪同期海水,δ^(18) O值为-15.38‰^-8.04‰,异常偏低,溶蚀区微量元素测定也反映了高Fe、高Mn、低Na的特征,指示了深部高温热液流体作用的存在。^(87)Sr/^(86)Sr值为0.705 368~0.715 889,表现为高于和低于微晶灰岩背景值2种类型,分别代表了壳源锶和幔源锶的特征。稀土元素配分曲线也表现为2种不同特征,一类右倾,正Eu异常,一类较平缓,负Eu异常,LREE/HREE值和(La/Yb)_N值也同时显示为较高值和高值2个部分,与基性和中酸性岩浆岩的稀土特征相似。反映了海西晚期塔河东南斜坡奥陶系受到了2种性质岩浆来源热液流体的影响,该热液流体沿疏导层运移对碳酸盐岩储层进行溶蚀产生孔洞、孔隙,同时伴随热液矿物的沉淀,但显著改善了储集物性,仍具有一定的储集意义,对深部碳酸盐岩储层的形成具有重要意义。

Two kinds of magma activities existed in the Tahe area,i.e.,basic and middle-felsic magma,coming from the mantle and crust respectively.The magma hydrothermal fluid could dissolve the Ordovician carbonate reservoir during its migration.The inclusion homogenization temperature of the karst-fractured-cavity calcite reaches 247℃,and the salinity is higher than that of the Ordovician seawater at the same period.The δ^（18） O value ranges from-15.38‰ to-8.04‰ and it is abnormally depleted.The trace elements have high level of Fe and Mn but low level of Na.All these indicate the existence of deep high temperature hydrothermal fluid.The ^（87）Sr/^（86） Sr ratio ranges from 0.705 368 to 0.715 889,which have two kinds,overtop and below the micrite,representing the crust source strontium and the mantle source strontium respectively.The distribution curve of rare earth element has two types,i.e.,one has right deviation and positive Eu exceptions,the other has relatively flat and negative Eu exceptions.The LREE/HREE and（La/Yb）_N display relatively high and higher values.The characteristics of the rare earth element are the same as the basic and middle-felsic magmatic rocks.It shows that the two kinds of magma recourse hydrothermal fluids influenced the Ordovician at Late Hercynian.The hydrothermal fluid moved along the channel layer and dissolved the carbonate reservoir,producing pore and hole with the hydrothermal minerals precipitation,which significantly improved the reservoir property,and had an important significance to the formation of deep carbonate reservoir.