恰什古伊地区碳氧同位素地层学分析

Carbon and Oxygen Isotope Stratigraphy Research in Chashgui Area

土库曼斯坦恰什古伊地区有效储集层为卡洛夫—牛津阶碳酸盐岩,该段GR变化小,旋回分析困难,导致有利储层预测难。利用该区Cha–21井所取岩芯中采集的41个样品测定的碳氧同位素,结合区域沉积演化分析资料,探讨了卡洛夫—牛津阶储层段沉积时的海平面变化。结果表明,氧同位素的原始信息已被成岩作用破坏,而碳同位素基本保持了原始特征,因此碳同位素可用于同位素地层研究和古环境分析;据此计算出盐度指数变化范围为128.25～136.63,明显大于海水和淡水的分界标准,反映成岩流体具有较高盐度海源水性质;由δ13C的变化所确定的研究区的海平面变化曲线与卡洛夫—牛津阶全球海平面变化曲线吻合,印证了该区储层地质年代定为卡洛夫—牛津期是准确的;依据海平面变化曲线,将卡洛夫—牛津阶主力储层段分为3个沉积旋回5个演化阶段。该成果填补了该区碳氧同位素地层研究的空白,对深化盆地沉积演化规律的认识及预测储层有利区块具有重要意义。

The effective reservoir in Chashgui Area,Turkmenistan,is Callovian-Oxfordian carbonate rocks. Since the GR curve does not varies much,it is difficult to predict the favorable reservoir distribution. Using the carbon and oxygen isotope from the 41 samples out of the core of the Well Cha-21 in Chashgui Area,combining with the data of the sedimentary evolution, this paper discusses the sea-level changes during the sedimentation of the Callovian-Oxfordian reservoirs. It is shown that the information in the oxygen isotope has been damaged,and the information in the carbon isotope has been preserved. So the carbon isotope can be used to study the isotope stratigraphy and analyze the Palaeo-environment. The calculated salinity index is 128.25～136.63,which is higher than the division standard between brine and freshwater,so the diagenetic fluid is high salinity brine. The carbon-isotope stratigraphic curve is almost consistent with the global sea-level curve,which proved that the reservoir geologic period is really Callovian-Oxfordian. According to the sea-level change curve,the main reservoirs in Callovian-Oxfordian are divided into 3 sedimentary cycles and 5 evolutionary phases. Those results fill up the blank in the isotopic stratigraphy studies,which are important significance for the in-deep understanding of the law of sedimentary evolution,and predicting the favorable blocks.