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受构造抬升运动的影响,塔里木盆地奥陶系碳酸盐岩多次暴露至地表遭受大气降水溶蚀改造,形成丰富的岩溶孔洞型油气储集空间.但钻井表明许多大型岩溶洞穴、小的孔洞、裂缝等遭受方解石的充填,造成储集性能变差.塔北地区奥陶系岩溶孔洞中所充填的方解石具有非常轻的氧同位素组成和高的87Sr/86Sr比值,其18OPDB位于21.2‰~13.3‰,平均值为16.3‰,87Sr/86Sr比值位于0.709561~0.710070,平均值为0.709843.同位素组成表明岩溶孔洞中所充填的方解石与大气降水有关.理论分析表明,大气降水对碳酸盐岩的溶蚀和充填作用受热力学和动力学双重机制控制.碳酸盐岩溶解的热力学因素决定大气降水在从地表向地下流动过程中对碳酸盐岩具有从溶解到饱和再到沉淀充填的作用特征,即地表之下大气降水对碳酸盐岩溶蚀作用发育的深度具有一定限度,而不能无限制的向深处发展;碳酸盐岩溶解的动力学因素控制着岩溶作用发育的强度、深度和广度,即岩溶作用还受地形地貌、气候、断裂/裂缝发育程度等多种因素制约.在热力学和动力学因素共同控制下,大气降水对塔里木盆地奥陶系碳酸盐岩的岩溶作用仅在不整合面之下一定深度(多数200 m)范围内发生,再往深处则会沉淀碳酸盐岩矿物,从而造成对已有空间的充填作用.
Affected by the tectonic uplift movement, the Ordovician carbonate rocks in the Tarim Basin exposed to the surface many times and were subjected to atmospheric erosion and alteration to form rich reservoirs of karst vugs, but drilling shows that many large-scale karst caves, small holes, Fissures and other calcations are filled by calcite, resulting in poor reservoir performance.The calcite filled in the Ordovician karst pores in the northern Tarim Basin has a very low oxygen isotopic composition and a high 87Sr / 86Sr ratio and its 18OPDB is between 21.2 ‰ and 13.3 ‰ , With an average of 16.3 ‰ and 87Sr / 86Sr at 0.709561 ~ 0.710070 with an average of 0.709843. The isotopic composition indicates that the calcite filled in the karst pores is related to precipitation. Theoretical analysis shows that the effects of precipitation on carbonate dissolution and The filling action is governed by the dual mechanisms of thermodynamics and kinetics.The thermodynamic factors of carbonate dissolution determine the characteristics of atmospheric precipitation from dissolution to saturation to sediment filling in the process of surface water flow from the surface to the ground, Under the atmosphere of the carbonate dissolution of the depth of development has a certain limit, but not unlimited development to the depths; carbonate The kinetic factors of karstification control the intensity, depth and breadth of karst development, that is, the karstification is also controlled by many factors such as topography, climate, degree of fracture / fracture development, etc. Under the common control of thermodynamics and kinetics, the atmosphere Precipitation affects the Ordovician carbonate karst in the Tarim Basin only within a certain depth (mostly 200 m) below the unconformity, and deeper sediments carbonate minerals, resulting in an increase of Space filling.