新疆塔河油田奥陶系碳酸盐岩溶洞、裂隙中方解石胶结物元素分析与成因

Chemical Analysis and Origin of Calcite Filled in and Cave With in Ordovician Carbonates in Tahe Oilfield,Xinjiang

通过对新疆塔河油田奥陶系的溶洞 (穴 )和裂隙充填的 31件方解石胶结物元素分析及因子和聚类分析表明 :①方解石中的CaCO3 、MgCO3 、FeCO3 、MnCO3 相对平均摩尔百分含量分别为 98.38%、0 .87%、0 .6 8%和 0 .0 7% ,SiO2 、Al2 O3 平均分别为 1.95 %、0 .73% ,Sr、BaO平均分别为 131.4× 10 6、5 16 .5× 10 6,F和Cl 平均分别为 0 .0 14 %和0 .0 13% ,而Mn +Fe/Mg、Mn/Fe平均分别为 0 .87、0 .10 ;②方解石中Sr/Ca =0 .0 0 6 18Mg/Ca + 0 .0 0 0 5 33( R2 =0 .197) ,主要显示出无机成因特点 ;③方解石常量与微量元素特征均可由六个因子可代表组成 ,具有一定的沉积与成岩作用意义 ;④据聚类分析将样品划分出四组 :其中 ,以S6 9 W 0 37等代表的可能为潜流带中的淡水淋滤的产物 ,并可能经历了相当强烈的水 岩作用或埋藏溶蚀作用 ;以S6 9 W 0 38等为代表的则为大气淋滤的产物 ;以S80 W 0 6 4等代表显示出埋藏作用或海水成岩及混合带的产物特征 ,但不排除埋藏热水作用的影响 ;S85 W 0 0 5等样品推测为海水浓缩背景下埋藏成岩产物 。

In order to elucidate origin and pattern of cement calcites filled in fissure and cave, thirty one calcite cement samples collected in cavity and fissure in Ordovician carbonate of Tahe oilfield ,Xinjiang were geochemically analyzed ,and the factor analysis and cluster analysis methods are used in such a large quantity of analytical data , the results show that: ①calcite cements are pure with the average mol% contents of CaCO 3,MgCO 3,FeCO 3 and MnCO 3 equal to 98.38,0.87,0.68 and 0.07, respectively, and average content of SiO 2,Al 2 O 3 equal to 1.95% and 0.73%,and Sr,BaO contain 131.4×10 6 and 516.5×10 6 as well as F and Cl equal to 0.014% and in 0.013%, and the average ratio of (Mn+Fe)/Mg and Mn/Fe equal 0.87 and 0.10,moreover, a linear covariance of Sr and Mg concentrations of calcites expressed by the following relationship: Sr/Ca= 0.00618 Mg/Ca+0.000533(R 2=0.197),which indicates the abiotic origin of calcites;②The six principle component consist of the major and trace elements with a certain of significant indication sedimentation factors and diagenetic environments; ③All of the samples can be divided into four groups in cluster analysis, among them, the first group represented by S67 W 037 and others document the characteristic of meteoric flushing product in phreatic zone and apparently undergone a series of strong water rock reactions or burial diagenetic reactions; the second group represented by S69 W 038 is characteristic of production of meteoric exposure , the third group represented by S80 W 064 related to marine environment or transition zone between meteoric and marine or burial diagenetic environment; However, it can not exclude the possibility of deep burial origin associated with thermal activities. While the fourth group represented by S85 W 005 is interpreted as burial origin with the high concentrated seawater, and appear to be related to a certain acidation under the reduction condition.