柴达木盆地小柴旦地区构造演化对烃源岩热演化的控制作用

柴达木盆地小柴旦地区是发育在元古界结晶基底上的中新生代叠合盆地,构造上具有南北分带的特征,形成6个典型的构造单元。中生代以来受燕山运动和喜山运动改造,形成两期区域不整合,不整合界面相互叠置,多期改造,且剥蚀作用涉及地层层系多、范围广。在主要不整合界面地层剥蚀量恢复基础上开展了骨干剖面构造演化研究,针对研究区具体情况采用针对性参数,系统开展了不同构造带中下侏罗统烃源岩埋藏史和热演化史分析。结果显示,不同构造带形成时期与四个演化阶段的沉降抬升幅度具有一定差异,构造演化的差异性也导致了中下侏罗统烃源岩在地质历史时期埋藏过程的差异性。区内烃源岩热演化可总结为山前推覆深埋型、持续埋深成熟型、抬升成熟型和抬升低熟型等四种类型。不同构造带烃源岩热演化的差异性也导致了研究区目前的油气发现主要集中于山前带及其周缘,但凹陷内也具备低熟油形成的条件。

The Controlling Effect of Tectonic Evolution on Source Rock Thermal Evolution in Xiaochaidan Area in Qaidam Basin

Xiaochaidan area in Qaidam Basin is a Mesozoic-Cenozoic superimposed basin which develops on Proterozoic crystalline basement, the structure is characterized by belts in S-N, six typical structural units are formed. Since the Mesozoic, the formations are rebuilt by Yanshan movement and Himalayan movement, two regional unconformities are formed, the unconformity surfaces overlap each other and are reformed in multiple periods, the erosion involves many formations and a wide range. Main section tectonic evolution study is done based on the erosion thickness restoration of the main unconformity surfaces, the results show that the formation periods of different tectonic belts and the subsidence and uplift range of the four evolution stage are both different, the differences of tectonic evolution results in the differences of Jurassic source rock burial processes in geological history. According to the specific conditions of study area, the burial history and thermal evolution history of middle-lower Jurassic source rocks in different tectonic belts are analyzed systematically by using appropriate parameters, comparison analysis indicates that the source rock thermal evolution in the study area can be summarized in four types: piedmont napping buried deeply type, buried continuously mature type, uplift mature type, uplift low maturation type. The difference of source rock thermal evolution in different tectonic belts also leads to the fact that the present hydrocarbon discoveries in the study area are mainly concentrated on the piedmont belts and their periphery area, but the depression also possess the condition of forming the low mature oil.