摘要:
由于充填物形成时流体性质和古水文环境不同,其碳氧同位素值也不同。因此,利用充填物碳氧同位素值可以判别缝洞充填过程中流体性质和古水文环境。通过对塔中Ⅱ区奥陶系鹰山组风化壳缝洞充填物测井曲线分析、岩芯观察与薄片鉴定,发现塔中Ⅱ区缝洞充填物测井显示一般为高 GR,主要为钙泥质充填物和角砾充填物。对充填物碳氧同位素进行分析并与基岩相比较,结果表明钙泥质充填物δ13 C 值为0.6‰~1.04‰,δ18 O 值为-6.8‰~-5.5‰,δ13 C 值明显偏正,由此认为溶洞中钙泥岩充填于良里塔格期海相环境;小角砾充填物δ13 C 值为-0.13‰,δ18 O 值为-6.29‰,与基岩值一致,判断为基岩垮塌或破碎充填形成。研究可为古岩溶缝洞储层充填机理研究和古岩溶模式建立提供依据。
Abstract:
This work is based on analysis of logging curves,core observations and thin section identification to fissure-cavity filings from Yingshan formation of Ordovician in the Tazhong II area,Tarim basin.The re-sults show that the fillings are of high GR values in logging curves and their lithology is dominated by calcar-eous-argillaceous material and breccias.Comparison of oxygen and carbon isotopes with bedrock indicates that the calcareous-argillaceous filling contains 0.6‰ to 1.04‰ ofδ1 3 C and -6.8‰ to -5.5‰ of δ1 8 O,of which the δ1 3 C value is obviously more positive.However,the δ1 3 C and δ1 8 O values of small breccia fillings are -0.13 ‰ and -6.29‰,respectively,consistent with that of bedrock.Both the fluid nature and ancient hydrological setting were variable when the fillings formed,resulting in different oxygen and carbon isotope values.Thus such values can be used to estimate fluid properties and ancient hydrological environment. Based on previous studies and the results of this test,we consider that the calcareous mudstone in caves was filled in a marine environment during the Lianglitage period and breccia fillings might be formed by collapsed or broken bedrock around caves.This recognition provides evidence for the study of filling mechanism in ancient karst fissure-cave reservoirs and establishment of paleokarst models.
下载: