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

QIAN Yi xiong; CHEN Yue; MA Hong xiang; CHEN Qiang lu

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.

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

1. Department of Resource and Environment, University of Petroleum,Beijing 102200;

2. Research Institute of Experimental Geology, CNSPC, Box 916,WuxiJiangsu 214151

Received Date: 2003-02-28

Rev Recd Date: 2003-06-26

Publish Date: 2004-03-10

Key words:

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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Reference (8)

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

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