神木北地区二叠系太原组储层流体包裹体特征与成藏期次

Characteristics of Fluid Inclusions and Hydrocarbon Accumulation Period of Permian Taiyuan Formation Reservoirs in Northern Shenmu

鄂尔多斯盆地北部神木地区二叠系分为几期成藏说法不一。本文通过对该区二叠系太原组储层流体包裹体进行岩相学特征观察、激光拉曼光谱特征分析、均一温度测试、盐度计算以及单井埋藏—热演化模拟等研究方法 ,综合判定油气成藏期次。岩相学和均一温度研究结果显示:包裹体组合Ⅰ中与烃类包裹体相伴生的盐水包裹体均一温度主要集中在70~110℃,丰度以盐水包裹体为主,少量CO_(2)包裹体,形状多为椭圆状,冰点温度在-5~-3℃之间,对应的盐度主峰值为7%,对应的油气充注时间为220~135Ma;包裹体组合Ⅱ中的盐水包裹体均一温度主要集中在110~140℃之间,丰度以盐水包裹体为主、CH_(4)包裹体次之,冰点温度在-15~-13℃之间,对应的盐度主峰值为18%,对应的成藏时间为135~100Ma。最终表明油气充注主要分为两个阶段,生烃作用从早侏罗世开始进入早期生烃阶段(J_(1)-J_(3)),随着埋深的逐步增加在早白垩世达到生气最高阶段(K_(1))。

There are various views on classification of hydrocarbon accumulation period in Permian of Shenmu,north of Ordos Basin.Through the petrographic observation,laser Raman spectrum analysis,homogenization temperature test,salinity calculation and single well burial-thermal evolution simulation of fluid inclusions in Permian Taiyuan Formation reservoirs,the periods of hydrocarbon accumulation are comprehensively determined.The results of petrographic and homogenization temperature studies show that in inclusion assemblage Ⅰ,the homogenization temperature of brine inclusions associated with hydrocarbon inclusions mainly concentrates at70-110℃,its abundance is dominated by brine inclusions,there are a few CO_(2) inclusions,whose shape is oval mainly,and freezing point is from-5 to-3℃,and the corresponding salinity peak is 7% and filling time of oil and gas is 220-135Ma.In inclusion assemblage Ⅱ,the homogenization temperature of brine inclusions mainly concentrates at 110-140℃,brine inclusions are the main and then CH_(4) inclusion with the freezing point from-15 to-13℃ and the corresponding salinity peak is 18% and hydrocarbon accumulation time is135-100Ma.Finally,it shows that there are two stages of hydrocarbon charge,hydrocarbon generation entered the early stage(J_(1)-J_(3)) from the early Jurassic,and the highest stage of gas generation(K_(1)) reached in the early Cretaceous with the gradual increase of burial depth.