柴达木盆地应力场特征与油气运聚关系

柴达木盆地早侏罗世以来经历了喜马拉雅运动晚期(中更新世末)、喜马拉雅运动中期(上油砂山期末)、燕山运动晚期(白垩纪末)和燕山运动早期(中侏罗世末)4次主要的构造运动。通过声发射法测得相应的最大主应力值分别为35.6～41.4,54.8～62.8,73.8和58.3 MPa。现今最大主压应力有效值为15.6～112.3 MPa,第三系油气主要成藏期古应力场的最大主压应力有效值为54.8～62.8 MPa。通过柴西地区主要成藏期应力场数值模拟和典型油气藏解剖,对柴西地区北西西断裂封闭史进行了分析,发现中新世晚期北西西向逆断裂对油气运移聚集具有双重性,断裂活动期主要起运移通道作用,而断裂静止期则相对封闭,主要起封堵油气的作用,使油气在断层上下盘都可以聚集成藏;油气主要在剪切应力值中等区域聚集成藏。

A discussion on relationship between tectonic stress field and migration and accumulation of hydrocarbons in Qaidam basin

Qaidam basin has experienced four major tectonic movements since Early Jurassic,including late Himalayan stage(end of Middle Pleistocene),middle Himalayan stage(end of upper Youshashanian),late Yan-shanian stage(end of Cretaceous) and early Yanshanian stage(end of middle Jurassic).The maximum principal stress values during the 4 major stages measured with acoustic emission(AE) method are 35.6～41.4,54.8～62.8,73.8 and 58.3 MPa,respectively.The current effective value of principal compressive stress is in the range of 15.6～112.3 MPa.The effective value of principal compressive stress during the main reservoiring stages of Tertiary oil and gas is in the range of 54.8～62.8 MPa.The sealing history of the NWW fault in western Qaidam basin is studied through simulating the stress fields during the major reservoiring stages and analyzing the typical oil and gas reservoirs in this area.It is found that the NWW reverse fault had dual effects on hydrocarbon migration and accumulation in late Miocene.It acted as hydrocarbon migration pathway during the active stage,and acted as seal during the ceasing stage,making hydrocarbons to accumulate both in the hanging wall and footwall of the fault.Hydrocarbons have accumulated mainly in the areas with moderate shearing stress.