川东南彭水地区下古生界脉体分形与古流体特征

VEIN FRACTAL AND PALEOFLUID FEATURES OF THE LOWER PALEOZOIC ERATHEM IN PENGSHUI AREA OF SOUTHEAST SICHUAN

四川盆地东南缘是目前四川盆地唯一未获得油气重大突破地区,烃类流体的动态保存条件是制约该区油气突破的重要原因。基于石油地质学、构造地质学相关理论,运用脉体分形学和流体地球化学对川东南彭水地区郁山背斜下古生界流体活动特征进行了相关研究。结果量化揭示出早古生代不同层系古流体活动脉体变差系数Cv在0. 68~1. 26变化,分维度值D均大于1,裂缝方向较为单一,以低角度或低开度裂缝为主,流体活动较强。脉体和围岩锶同位素比值测量表明不同层系中^(87)Sr/^(86)Sr值普遍大于同期海水的^(87)Sr/^(86)Sr值,均受到外源高锶流体的改造,揭示出该区较强的流体活动特性和相对较弱的油气保存条件。综合判定彭水地区下古生界海相碳酸盐岩储层勘探潜力较差。

The southeast margin of Sichuan basin is currently only for breakthrough area in oil and gas for the basin,the dynamic preserving conditions of the hydrocarbon fluid are the important reason of the oil and gas breakthrough in the region. Based on the theories of petroleum geology,structural geology,with the help of the vein fractal theory and fluid geochemistry,the flow characteristics of Lower Palaeozoic fluids were researched for Yushan Anticline in Pengshui area of Southeast Sichuan. The achievements show that the variation coefficient（ Cv） of the active veins in different layers of Early Paleozoic era changes from 0. 68 to 1. 26,the fractal dimension values（ D）are greater than 1,the fracture direction is relatively simple,the low-angle or low-opening crack is prior,andmoreover the activity of the fluid flow is rather stronger. The measurements of the strontium isotope ratios of the vein body and surrounding rock show that different ^87Sr/^86Sr values in various layers are generally greater than those of the same ratio of the sea water at the same period,and furthermore both of the values were reformed by the outside-source high-strontium fluids,thus rather strong fluid flow characteristics and relatively weak oil and gas preserving conditions were revealed in the region. It is comprehensively judged that the exploration potential of Lower Palaeozoic marine carbonate reservoirs is rather poorer.