Petrology and carbon-oxygen isotope of inorganic CO_2 gas reservoir in Wuerxun depression,Hailaer basin.
Petrology and carbon-oxygen isotope of inorganic CO_2 gas reservoir in Wuerxun depression,Hailaer basin.
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作者：
Gao Yu
海拉尔盆地乌尔逊凹陷CO_2气藏砂岩中富含片钠铝石，为研究CO_2在砂岩上的风蚀作用和自生矿物组合的形成提供了天然的实验室。利用偏振显微镜、扫描电镜、X射线衍射和MAT253稳定同位素等研究了胶结物和自生矿物的类型、共生序列以及形成片钠铝石的CO_2成因。前CO_2矿物有方解石、石英增生和高岭石。石英增生生长过程中注入第一阶段油气。CO_2注入储层晚于第一阶段油气。CO_2流入后，主要胶结物为片钠石和铁白云石。CO_2流入后注入油气第二阶段。片钠石δ~(13)C值范围为-5.3与片钠石同位素平衡的CO_2气体的δ~(13)C计算值范围为-10.7~-7.0‰PDB,与海拉尔盆地无机CO_2气体的δ~(13)C值(-11.36～-8.02‰PDB)相吻合。这些值表明形成片钠石的CO_2和气藏的形成均来自于混合背景。有机CO_2主要来自于无机CO_2。根据片钠钙石内砂岩和CO_2气藏均位于深部断裂和γ5花岗岩附近，气藏中的CO_2和形成片钠铝石的CO_2均属于地幔成因-岩浆类型。片钠岩内砂岩保存了CO_2驱油的证据。
The CO_2 gas reservoir sandstone of Wuerxun Depression in Hailaer Basin,with abundance of dawsonite,provide a natural laboratory to study the aheration of CO_2 on sandstone and the forming of authigenic mineral assemblage.The types,paragenetic sequence of cements and authigenic mineral and origin of CO_2 forming dawsonite are investigated using palarizering microscope, scanning electron microscope,X-ray diffraction and MAT253 stable isotope mass spectrometer.Pre-CO_2 minerals include calcite, quartz overgrowth and kaolinite.The first stage of oil and gas injected during the quartz overgrowth growing.CO_2 injecting reservoir is later than the first stage of oil and gas.After CO_2 influx,the main cements are dawsonite and ankerite.The second stage of oil and gas injected after CO_2 iuflux.Dawsoniteδ~(13)C values range from-5.3 to-1.5‰PDB.The calculated δ~(13)C values of CO_2 gas in isotope equilibrium with dawsonite range from-10.7 to-7.0‰PDB,in coincidence with δ~(13)C values(-11.36～-8.02‰PDB)of inorganic CO_2 gas in Hailaer Basin.These values indicate that CO_2 both forming dawsonite and from gas reservoir originates from mixture background of hmrganie and organic CO_2 mostly from inorganic CO_2.According to the fact that both sandstone within dawsonite and CO_2 gas reservoir lie in the vicinity of deep fracture and γ5 granite,CO_2 both from gas reservoir and forming dawsonite ahnost belong to type of mantle origin-magma.The sandstone within dawsouite preserved the evidence of oil displaced by CO_2.