塔里木盆地热液活动地质地球化学特征及其对储层影响

塔里木盆地二叠纪时发生了强烈的岩浆-火山作用,与之相关的热液流体沿着断裂、裂缝以及不整合面活动,并与所经碳酸盐岩围岩发生反应,使围岩发生不同程度的溶蚀改造,主要表现在:1热液溶蚀和热褪色现象显著;2沉淀生成多种热液矿物组合,如萤石-石英组合、闪锌矿-绿泥石-方解石组合,重晶石-石英-黄铁矿-菱铁矿组合等;3热液作用区域碳酸盐岩成分发生了明显的变化,主要表现为Fe、Mn、Si等元素含量的升高,比正常灰岩高出几倍至几十倍。上述特点与岩溶作用和成岩溶蚀作用特征明显不同。对典型钻孔碳酸盐岩储层研究表明,无论灰岩还是白云岩,在热液作用下都会产生大量的微小溶蚀孔洞,储层物性得到明显的改善,因此热液作用是影响储层物性不可忽视的重要因素。

Geological and Geochemical Signatures of Hydrothermal Activity and Their Influence on Carbonate Reservoir Beds in the Tarim Basin

Intensive igneous activities took place in the Tarim Basin in the Permian. Hydrothermal fluids were derived from igneous activities, migrated along faults and fractures and reacted with carbonate host rocks. When carbonates are dissolved by hydrothermal fluids, some mineral assemblages, typical of hydrothermal genesis, would precipitate from the hydrothermal fluids. The mineral assemblages include (1) fluorite-quartz, (2) sphalerite-chlorite-calcite and (3) barite-quartz-pyrite-siderite assemblages. The carbonates are relatively enriched in Fe, Mn and Si, where the carbonates were partially dissolved by hydrothermal fluids. Under the influence of hydrothermal fluids, numerous dissolution pores of few millimeter were created, and consequently the porosity and permeability of carbonate reservoir beds were significantly enhanced. The enhancement in porosity and permeability is very important for carbonates to be efficient oil and gas reservoir beds, particularly for those that have not experienced subaerial karst.