川东邻水-渝北地区石炭系古岩溶储层稀土元素地球化学特征

石炭系黄龙组岩溶岩系是川东邻水-渝北地区天然气藏最重要的储层类型之一,依据岩溶岩的结构特征,将黄龙组岩溶岩系划分为弱溶蚀岩溶岩、中等溶蚀多孔状岩溶岩、强溶蚀角砾状岩溶岩和强溶蚀交代次生灰质岩溶岩等4种类型.岩溶岩中发育有淡水方解石和淡水白云石2种胶结物类型,以及再埋藏期沉淀的热液异形白云石.稀土元素分析结果表明,不同岩石结构、成分和不同溶蚀强度的岩溶岩及其胶结物的地球化学特征有显著差异,证明稀土元素的迁移、配分、富集和异常效应不仅可以判别岩溶过程中的流体性质和古水文条件,同时也可作为评价和预测古岩溶储层的重要标志之一.

REE geochemical characteristics of paleokarst reservoirs in Huanglong Formation of Linshui (eastern Sichuan) - northern Chongqing area

The carbonatite paleokarst rocks of Upper Carboniferous Huanglong Formation constitute one of the most important natural gas reservoirs in Linshui of eastern Sichuan-northern Chongqing area. Based on structural features of karst rocks, the authors have divided the karst rocks of Huanglong Formation into four types, namely slightly corroded karst rock, medium degree corroded and porous karst rocks, strongly corroded brecciated karst rocks and strongly corroded and altered secondary gray-karst rocks. Moreover, two types of cements of limnic calcite and limnic dolomite and hydrothermal dolomite of reburial period are included in the karst rocks. A synthetic analysis of geochemical characteristics of rare earth elements has led to the conclusion that karst rocks or cements of different rock textures, components and corrosion intensities obviously have different REE geochemical characteristics. It is thus thought that the migration, distribution, enrichment and abnormal effects of the REE can not only be used to distinguish fluid properties and paleo-hydrologic conditions but also serve as one of the important indicators for evaluating and forecasting paleokarst rock reservoirs.