塔里木盆地塔河油田中下奥陶统鹰山组内幕储层成因机理

塔里木盆地塔河油田中下奥陶统顶部风化壳缝洞型储集体是主力产层，在其下部依然发育规模性储集体，为探讨这套储集体的成因机理，在A井区开展了碳氧同位素、锶同位素、稀土元素和阴极发光等分析测试工作。洞穴和构造裂缝方解石的δ18O和δ13C值明显比灰岩背景值偏负，具有δ18O不变而δ13C可变的趋势，δ18O_PDB均值为-14.74‰，为脱气作用形成的大气水方解石线。洞穴和构造裂缝方解石的87Sr/86Sr比值介于0.709 622～0.709 968之间，明显高于背景值，主要受壳源锶的影响；稀土元素中Ce和Eu元素无正异常，表明缺乏热液流体的参与。洞穴和构造裂缝方解石胶结物主要发橘黄色和暗棕色光，代表的是弱氧化—弱还原环境。研究认为，A井区中下奥陶统鹰山组缝洞储集体形成于海西早期大气淡水深部缓流带环境，该岩溶环境具有承压、水流缓慢、不受排水基准面控制的特点。 

Genetic mechanism of inner reservoirs of Yingshan Formation of Middle-Lower Ordovician in Tahe Oil Field,Tarim Basin

The fracture-cave reservoirs of weathering crust on the top of Middle-Lower Ordovician in the Tahe Oil Field of Tarim Basin are the major production layer, and large scale reservoirs are also developed underneath the reservoirs. In order to discuss the genetic mechanism of formation of these reservoirs, carbon and oxygen isotope, strontium isotope, rare earth elements and cathodoluminescence were tested in the well A area. The δ18O and δ13C values of calcite in caves and structural fractures are obviously negative than those in limestone background. The mean value of δ18O_PDB is -14.74‰, showing a trend of constant δ18O and variable δ13C, which are the calcite lines of atmospheric water formed by degassing. The 87Sr/86Sr ratios of calcites from caves and structures range from 0.709 622 to 0.709 968, which are obviously higher than the background values, and are mainly affected by crustal strontium. There are no positive anomalies in Ce and Eu elements, indicating that there is no hydrothermal fluid involved. The cathodoluminescence of calcites are mainly orange and dark brown, which represents weak oxidation-reduction environment. The results showed that the fracture-cave reservoirs of the Midde-Lower Ordovician Yingshan Formation in the well A area were formed in the deep slow flow zone of atmospheric water during the Early Hercynian, showing the characteristics of pressure bearing, slow flow and not controlled by the karst drainage base level.