黔北灯影组自生石英流体包裹体特征及油气成藏演化

摘要

系统分析了黔北仁怀县震旦系灯影组储层孔洞充填自生石英、方解石流体包裹体特征及氧同位素组成,采用下寒武统牛蹄塘组沥青反射率并结合灯影组自生石英流体包裹体均一温度进行古地温场恢复.研究结果表明,自生石英流体包裹体可以分为三期,均一温度分别为87. 1～98. 8℃、109. 4～126. 8℃和171. 3～190. 2℃,晚期充填方解石流体包裹体均一温度为95. 3～116. 4℃,下寒武统牛蹄塘组等效镜质体反射率为3. 11% ～3. 43%.结合包裹体均一温度分析,认为加里东晚期—燕山期古地温梯度为2. 61～2. 76℃/100m,各期埋藏阶段充填白云石和晚期充填方解石δ18O(PDB)分别为-15. 0‰～-7. 8‰和-16. 1‰～-14. 2‰,估算其形成的温度分别为92. 0～212. 5℃和74. 5～86. 3℃.黔北仁怀灯影组发生了三期油气成藏及一期天然气藏破坏,分别为加里东中晚期浅埋藏首次石油成藏(442～428Ma)、海西晚期—印支早期中等埋深二次石油成藏(252～232Ma)及燕山早期深埋天然气成藏(170Ma～155Ma),喜马拉雅早期天然气藏破坏时间约为42～30Ma,破坏深度为2963～3741m.本研究对于该区"下组合"油气勘探部署具有重要意义.%The study of stages and processes of the Sinian hydrocarbon accumulationis of important significance in the oil and gas exploration and deployment of the "Lower Association"petroliferous system in northern Guizhou. In this paper,the emphasis is placed on systematic analysis of fluid inclusions and oxygen isotope compositions in authigenic quartz and calcite as the pore-space fillings from the hydrocarbon reservoirs in the Sinian Dengying Formation in Renhuai,northern Guizhou. The reconstruction of paleogeothermal fields is based on bitumen reflectances of the Lower Cambrian Niutitang Formation in combination with the homogenization temperatures of fluid inclusions in authigene quartz in the Dengying Formation. The results of research have proved that the fluid inclusions occurring in authigenic quartz can be divided into three stages,with homogenization temperatures of 87. 1-98. 8℃,109. 4-126. 8℃ and 171. 3-190. 2℃, respectively. The homogenization temperatures of fluid inclusions in calcite filled in the later stages range between 95. 3℃ and 116. 4℃. The equivalent vitrinitere flectances of the Lower Cambrian Niutitang Formation vary from 3. 11% to 3. 43%. Judged from the homogenization temperatures of the fluid inclusions, it is believed that paleogeothermal gradients in the late Caledonian-Yanshanianmay vary from 2. 61℃/100 m to 2. 76℃/100 m. The δ18OPDB values range from -15. 0‰to -7. 8‰for dolomite filled in individual stages,and from -16. 1‰ to -14. 2‰for calcite filled in the later stages. It is inferred that the formation temperatures are estimated to be 92. 0-212. 5℃ and 74. 5-86. 3℃,respectively. Three stages of oil and gas accumulation and one stage of gas reservoirs destruction are recognized,including the first stage of oil and gas accumulation during the middle to late Caledonian shallow burial stage (442-428 Ma);the second stage of oil and gas accumulation during the late Hercynian to early Indosinian medium burial stages (252-232Ma);the third stage of gas accumulation during the early Yanshanian deep burial stage (170-155Ma ),and one stage of gas reservoirs destruction during the early Himalayan (ca. 42-30Ma)at the depths of 2963-3741m in the Dengying Formation in Renhuai,northern Guizhou.