塔里木盆地塔深1井超深层白云岩储层成因新认识:来自原位碳氧同位素分析的证据

New insights of the genesis of ultra-deep dolomite reservoirs in Well TS1,Tarim Basin:Evidence from in situ carbon and oxygen isotope analysis

塔里木盆地超深层钻井塔深1井揭示在埋深8 408 m条件下依然具有优质白云岩储层,但储集空间的成因机制存在较大争议。在详细的岩心描述、显微岩石学观察与孔洞胶结物充填序列分析基础上,对阴极发光分析后的加厚薄片,通过原位微区取样方法分别获取基质、早期白云石胶结物和晚期白云石胶结物样品并进行碳氧同位素分析。早期白云石胶结物与白云岩基质具有相对一致的碳氧同位素分布特征,而晚期白云石胶结物δ13C值和δ18O值偏负。胶结物充填序列与碳氧同位素分析结果表明,不同类型白云石是多阶段白云石化作用的产物,即孔洞在白云石化作用发生的时候已经形成并随着埋深增加不断消亡。中寒武统阿瓦塔格组深灰色孔洞型白云岩储集空间的形成可能与准同生期近地表成岩事件有关。

The ultra-deep Well TS1 in the Tarim Basin revealed high-quality dolomite reservoirs at the depth of 8 408 m,but the genesis mechanism of the reservoir space is controversial. Based on detailed core description,microscopic petrological observation,and analysis of filling sequence of the cements in pores,micromill sam-ples of matrix,early dolomite cements and late dolomite cements were obtained by in situ sampling method after the cathodoluminescenece analysis of the thickeded thin sections and analyzed for carbon and oxygen isotopes. The early dolomite cements and the dolomite matrix had relatively consistent results of carbon and oxygen isotope distribution characteristics,while the later dolomite cements had more negative δ13C and δ18O values. The cements filling sequence in pores and carbon and oxygen isotope analysis results show that different types of dolomite are the products of multi-stage dolomitization,which means that pores had been formed when the the dolomitization occureed and continued to disappear with increasing depth. The formation of the dark gray dolomite reservoir space of Avatage Formation in the Middle Cambrian should be related to the near-subsurface diagenetic events during the penecontemporaneous period.