塔里木油气区砂岩储集层碳酸盐胶结物的同位素组成与成因分析

Stable isotopic composition and origin analysis of the carbonate cements within sandstone reservoirs of Tarim oilgas bearing area.

塔里木油气区的砂岩储集层中，以胶结物形式存在的方解石相当普遍，并直接影响砂岩储集性能。应用同位素示踪原理探讨砂岩储集层中碳酸盐胶结物的来源及形成机理十分必要。根据碎屑岩油气藏在塔里木盆地分布特点，选择了７个主要含油气区块及含油层系的砂岩样品，进行了碳酸盐胶结物碳、氧稳定同位素分析。认为：部分志留系、石炭系以及二叠系、泥盆系的砂岩碳酸盐胶结物为“成岩碳酸盐”，其形成与油气无关。侏罗系、三叠系和石炭系的大部分砂岩碳酸盐胶结物同位素组成显示其成因为与有机质有关的碳酸盐，即有机质在热催化作用下产生了烃类与ＣＯ２，这时的ＣＯ２与油气一道进入储集层，并与Ｃａ２＋结合，以碳酸盐胶结物的形式沉淀。由此可以判断与油气有关的砂岩储集层及分布地区。东河塘石炭系砂岩中碳酸盐胶结物的同位素特征显示出，该套砂岩经过了抬升－浅埋受大气淡水淋滤，又再次埋深的埋藏历程，这是该区形成优质储集层的一个主要因素。

Based on the characters of clastic oil and gas reservoirs distributed in Tarim basin, the carbonated cements within sandstone samples of oil and gasbearing taken from seven major oilgas provinces have been isotopically analyzed in this study. The results show that part of the cements in sandstones of Silurian, Carboniferous, Permian and Devonian are diagenetic carbonates that have no relationship with the oil and gas generating. The isotopic compositions of most carbonate cements in Jurassic, Triassic and Carboniferous sandstones, however, have reflected a stronger origin relationship with organic material, suggesting that they should be a precipitation of carbonate cements connected between Ca2+ ions and CO2 generated from hydrocarbons under the thermalacceleration. Then, the clastic reservoirs and areas, having relationship with oilgas distribution, will be able to be distinguished. The stable isotopic composition of carbonate cements within the Carboniferous sandstones in Donghetang region suggest that the sandstone has had a sequence of liftshallow buriedatmospheric fresh water leached and buried deeply again, and reflect a major factor of high quality reservoirs formed in this area. The calcite cements are widely distributed within sandstones of Tarim basin, which directly affect the quality of reservoirs. So, the stable isotopic studies should be a useful and practical tool for distinguishing the origin and form of the cements and the petroleum exploration in this area.