鄂尔多斯盆地长6油层组古盐度研究

STUDY ON PALAEOSALINITY OF CHANG 26 OIL RESERVOIR SET IN ORDOS BASIN

郑荣才 柳梅青

Zheng Rongcai Liu Meiqing

以硼、“相当硼”、K+Na含量、K/Na比值、吸附K′+Na′、锶含量以及Sr/Ba比值等地化指标作为古盐度的判识标志,运用亚当斯和科奇古盐度计算公式,对鄂尔多斯盆地长6油层组沉积环境的古盐度进行分析和计算,结果表明长6油层组沉积时湖泊水体的古盐度为0.940%～1.016%,属富钠的微咸-半咸水环境。经分析比较,上述古盐度判识标志中,K+Na含量及K/Na比值与长6油层组的古盐度无明显对应关系,不能作为判识标志;而硼、”相当硼“、吸附K′+Na′、锶含量及Sr/Ba比值等地化指标较为灵敏,对古盐度的判识较为可靠。将多种指标判识的结果作回归分析后,认为科奇公式计算的结果最为可靠。古盐度的确定不仅可以判断湖泊水体类型,而且对了解生油岩系的发育情况和分析浊沸石化作用的钠组分来源都大有帮助。

Take the geochemical indicators of boron,equivalent boron,adsorptive K+Na,Sr and the ratio of Sr/Br etc.as palaeosalinity indicators,the palaeosalinity of Chang6 oil reservoir set in Ordos Basin is analysed and calculated by using the formula advanced by T.D.Adams and E.L.Couch.The results indicate that the Late Triassic Ordos Basin is not an inland fresh water lake as recognized for a long time,but a brackish water to semisalt water marginal lake caused by intermittent seawater ingression.The paleosalinity of water body of the reservoir set was 0.940%～01.016% during its deposition.The contents of K+Na and the ratio of K/Na in the above mentioned paleosalinity do not correspond with that of Chang 26 reservoir set;the contents of boron,equivalent borom, adsorptive K+Na,Sr and Sr/Ba ratio are reliable identifying indicators of the paleosalinity.After the regression analysis of the identifying results of various indicators,it is suggested that the results calculated by E. L. Couch formula are more reliable.The identificatin of paleosalinity could not only distinguish the water type of paleolake,but also could know the evolution of source rock.

10.11743/ogg19990105