Abstract This article explores the footprints of hydrocarbon microseepage in the Upper-Red Formation covering the Alborz petroleum reservoir in the Saveh-Qom basin, Iran. The adopted multidisciplinary approach combines field observation and sampling, detailed petrographical and geochemical analysis, and remote sensing mapping using Sentinel-2 and ASTER satellite data. The study revealed significant changes in the microseepage-affected zones when contrasted to unaffected lithofacies and led to the establishment of a new array of mineralogical and geochemical indicators for the phenomenon. These comprise partial bleaching of the red-beds, secondary goethite coatings, diagenetic clay minerals (e.g. illite-smectite, chlorite), and pervasive calcite, silica, and gypsum cementations. In terms of geochemistry, the major oxides, particularly the ratio of CaO + K2O/Na2O + MgO + CaO + K2O proved to be a reliable index for distinguishing microseepage-prone areas. Based on isotopic studies, a combination of three sources of carbon, comprising oxidized hydrocarbons, was recognized in the carbonate cements; yet the strata were shown to be moderately flushed by percolating fluids. Satellite remote sensing was successful in mapping reservoir-scale footprints of the microseepage systems. It indicated that the extent of the induced alterations, and thereby the outline of the underlying reservoir, is much larger than previously known. Overall, the secondary changes were shown to be a function of the geochemistry of the host-rock, the local environmental variables (i.e. climate and hydrogeology), and the 3D architecture of the trap. The substantiated indicators carry direct implications for onshore microseepage targeting and hold high potential to help reduce the exploration and development risks in frontier and mature basins.

中文翻译：

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伊朗库姆地区上红组微渗流引起的成岩变化特征。第一部分：露头、地球化学和遥感研究

摘要 本文探讨了伊朗 Saveh-Qom 盆地 Alborz 油藏上红色地层中碳氢化合物微渗流的足迹。所采用的多学科方法结合了现场观测和采样、详细的岩相和地球化学分析，以及使用 Sentinel-2 和 ASTER 卫星数据的遥感测绘。该研究揭示了与未受影响的岩相相比，受微渗流影响的区域发生了显着变化，并导致为该现象建立了一系列新的矿物学和地球化学指标。这些包括红层的部分漂白、次生针铁矿涂层、成岩粘土矿物（例如伊利石-蒙脱石、绿泥石）和普遍的方解石、二氧化硅和石膏胶结物。在地球化学方面，主要的氧化物，特别是CaO + K2O/Na2O + MgO + CaO + K2O 的比例被证明是区分微渗漏区域的可靠指标。根据同位素研究，在碳酸盐胶结物中识别出三种碳源的组合，包括氧化碳氢化合物；然而，地层显示被渗透流体适度冲刷。卫星遥感成功地绘制了微渗流系统的水库尺度足迹。这表明，诱发蚀变的程度以及下伏储层的轮廓比以前已知的要大得多。总体而言，次生变化被证明是主岩地球化学、当地环境变量（即气候和水文地质）以及圈闭的 3D 结构的函数。