Chemical Analysis and Origin of Calcite Filled in and Cave With in Ordovician Carbonates in Tahe Oilfield,Xinjiang
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摘要: 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 、Al2O3 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,可能出现酸性还原条件.Abstract: In order to elucidate origin and pattern of cement calcites filled in fissure and cave,thirty-one calcite ce-ment samples collected in cavity and fissure in Ordovician carbonate of Tahe oilfield,Xmjiang were geochemicallyanalyzed,and the factor analysis and cluster analysis methods are used in such a large quantity of analytical data,the results show that:1.alcite cements are pure with the average mol%contents of CaCO3,MgCO3,FeCO3 andMnCO3 equal to 98.38,0. 87,0. 68 and 0. 07,respectively,and average content of SiO2,A12O3 equal to 1.95%and0. 73%,and Sr,BaO contain 131.4 X10-6 and 516. 5 X10-6 as well as F and C1 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 andMg concentrations of calcites expressed by the following relationship:Sr/ Ca=0. 00618Mg/ Ca+0.000533(Rz=0. 197),which indicates the abiotic origin of calcites;The six principle component consist of the major and traceelements with a certain of significant indication sedimentation factors and diagenetic environments;all of thesamples can be divided into four groups in cluster analysis,among them,the first group represented by S67-W 037and others document the characteristic of meteoric flushing product in phreatic wne and apparently undergone a se-ries of strong waterrock reactions or burial diagenetic reactions;the second group represented by S69-W 038 ischaracteristic of production of meteoric exposure,the third group represented by S80-W 064 related to marine en-vironment or transition zone between meteoric and marine or burial diagenetic environment;However,it can notexclude the possibility of deep-burial origin associated with thermal activities. While the fourth group representedby S85-W 005 is interpreted as burial origin with the high concentrated seawater,and appear to be related to a cer-taro acidation under the reduction condition.
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Key words:
- calcite /
- chemical analysis /
- factor analysis /
- cluster analysis /
- origin of cements /
- Tahe oilfield
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