摘要
近年来，柴西地区始新统致密碳酸盐岩中的油气勘探获得了重要进展，其中白云岩为最优质的储集岩。系统的岩石学、矿物学和地球化学特征研究表明，该套白云岩主要为泥晶结构，白云石晶间孔广泛发育，孔径多小于1μm。泥晶白云岩的δ^13CPDB值变化范围为-4．5‰-0．2‰，平均值为-2．4‰，相对于典型湖相碳酸盐岩偏负，反映了周缘辫状三角洲供给富含轻碳的地表水在一定程度上改变了白云岩的碳同位素组成，且湖水中的溶解碳部分来源于有机质氧化解体产生的CO2，通过改变湖水中溶解碳的碳同位素组成从而间接影响了湖相白云岩的碳同位素组成。泥晶白云岩的δ^18OPDB值变化范围为-6．1‰-0．4‰，平均值为-2．6‰，相对于典型湖相碳酸盐岩偏正，明显受咸化湖沉积环境影响。碳氧同位素相关关系投点图及其计算出的盐度、温度数据反映了泥晶白云岩是在准同生阶段、半开放．半封闭的咸化环境下、于水／沉积物界面附近由方解石交代而成的低温白云岩，这类准同生交代成因白云岩在区域上分布较广，且孔径极小的白云石晶间孔抗压实能力强，这一重要发现无论是平面展布上还是纵向深度上均开拓了柴达木盆地致密油勘探的新领域。
In recent years important progress has been made in exploring petroleum of dense carbonate reservoirs of Eocene Epoch in Western Qaidam Basin. Among the carbonate rocks of reservoirs, dolomite proves to be the high quality reservoir rock type. In this research the petrological, mineralogical and geochemical characteristics of saline lacustrine dolomite from Lower Eocene Ganchaigou Formation in western Qaidam Basin were studied, and our results show the following conclusions： The structures of the dolomite sequence are mainly micritie, with intercrystal pores （less than 1μm） being developed extensively. For micritic dolomite the δ^13CPDB values range from -4.5‰ to 0.2‰, with the average of-2.4‰, while the δ^13C is biased negatively as compared to that for typical lacustrine carbonates. This reflects that the braided delta around the dolomite supplies rich light carbon surface water which to a certain extent changes the carbon isotopic composition of the dolomite and that part of the dissolved carbon in the lake may come from CO2 resulted from organic matter oxidation or disintegration. The organic matter enriched in light carbon renders the dissolved carbon＇s isotopic composition lighter, thus modifies the carbon isotopic composition of lacustrine deposit dolomite indirectly. For micritic dolomite the δ^18OPDB values range from -6.1‰ to 0.4‰, with the average value of-2.6‰, while the δ^18O is biased positively as compared to that for typical lacustrine carbonates because it is significantly affected by saline lacustrine environment. The oxygen and carbon isotope correlation diagrams and the salinity and temperature data all reflect that the micritic dolomite is formed in semi-open and semi-closed saline environment on penecontemporaneous stage through metasomatism of calcite on the water/sediment interface and under low temperature environment. This kind of penecontemporaneous metasomatism-derived dolomite is extensively distributed in the study area, and the intergranular pores of small aperture in dolomite have strong anti-compaction capability. We believe this important discovery would open up new fields of oil exploration, in terms of plane distribution or vertical depth, in dense dolomite reservoirs in Qaidam Basin.
出处
《地球化学》
CAS
CSCD
北大核心
2015年第3期254-266,共13页
Geochimica
基金
国家油气专项(2011ZX05003)
中国石油重大科技专项(2011E-03)
关键词
准同生
白云岩
晶间孔
碳氧同位素
成化湖盆
柴达木
penecontemporaneous
dolomite
intergranular pore
carbon and oxygen isotope
saline lacustrine basin
Qaidam
作者简介
袁剑英（1965-），男，博士、教授，从事石油地质勘探与地球化学研究工作。E—mail：yuanjy@petrochina．com．cn
通讯作者（Corresponding author）： HUANG Cheng-gang, E-mail： 12664018@qq.com; Tel： ＋86-931-8686343
