塔里木盆地玉北地区奥陶系缝洞充填方解石地球化学特征及其储层流体分析

Geochemical characteristics and fluid origins of fracture- and cave-filling calcites of Ordovician in Yubei area, Tarim Basin

李淼 周雨双 赵永强 耿锋 乔桂林 郝建龙

LI Miao ZHOU Yushuang ZHAO Yongqiang GENG Feng QIAO Guilin HAO Jianlong

中国石化 石油勘探开发研究院 无锡石油地质研究所, 江苏 无锡 214126 中国石化 西北油田分公司 勘探开发研究院, 乌鲁木齐 830011

Wuxi Research Institute of Petroleum Geology, SINOPEC, Wuxi, Jiangsu 214126, China Research Institute of Exploration and Production, Northwest Oilfield Company, SINOPEC, Urumqi, Xinjiang 830011, China

塔里木盆地玉北地区奥陶系碳酸盐岩储层的成因是该地区油气勘探研究的关键问题。通过分析玉北地区奥陶系碳酸盐岩缝洞方解石的充填特征和地球化学特征，并结合区域构造背景，探讨了影响储层发育的流体期次、性质和作用类型。该区奥陶系缝洞充填方解石样品的稀土配分曲线呈现淡水和海水2种流体特征，由东向西分布的井中样品锶同位素比值逐渐减小，且高角度缝方解石的锶同位素值明显高于孔洞和水平缝洞方解石中的，显示了不同区域、不同产状样品中流体性质的差异。因此，玉北地区奥陶系碳酸盐岩成岩系统具有一定开放性，由东向西淡水改造的程度逐渐减弱，这与加里东中期—海西早期东强西弱的构造活动特征相吻合，断裂活动强度影响了流体对储层的改造过程。

The genesis of carbonate reservoirs of the Lower-Middle Ordovician strata has been an important topic for petroleum exploration in the Yubei area, Tarim Basin. To investigate the stages and properties of paleo-fluid and discuss the reservoir origin, the geochemical and cathodoluminescence features of the Ordovician fracture- and cave-filling calcites from wells in the Yubei area were analyzed combining with the regional tectonic background. Results show that the REE distribution patterns and occurrences of samples from different wells have the characteristics of seawater and fresh water, respectively. The average values of Sr isotopes gradually decrease from east to west. Moreover, the average value of 87Sr/86Sr in high-angle fracture calcites is higher than those of cave-filling and horizontal-fracture calcites, suggesting obvious variations of fluid properties in different regions and sample occurrences. Therefore, the diagenetic environment of the Lower-Middle Ordovician carbonates in the Yubei area may be open. The decreases of meteoric alteration from east to west can be attributed to the Middle Caledonian and Early Hercynian tectonic setting. Moreover, the progress of reservoir modification by fluids is mainly affected by fault activity intensity.

中国石化科技部项目“塔西南下古生界油气富集关键因素及突破目标评价” P19022-6

https://doi.org/10.11781/sysydz202204593