叠合盆地构造-热演化动态过程的低温热年代学研究

Marine petroleum resource is one of the most important hot points for oil and gas exploration in China in recent years. Most marine strata in China occurrence in the polycyclic superimposed reconstructed basin, superimposed basin or/and complicated alternate residual basin. The hydrocarbon exploration for such basins is facing many problems and challenges, in which the deep marine reservoirs formation, transformation and preservation under the control of the complex the tectonic regime conversion, structural superimposed under the control of composite and thermal history during the late Mesozoic - Cenozoic tectonic movements superimposed and the transformed process is one of the most critical Challenge. In this research, take the typical superimposed basin, Jianghan Plain of the Mid Yangtze region in Southern China as an example, based on the traditional basin analysis and petroleum geology technology, aimed at the role of scientific problems that the dynamic process of tectonic and thermal evolution of the superimposed basin and its controlling on deep marine petroleum reservoir formation, redistribution and transformation, exploring the use of the international emerging low-temperature thermochronology dating(fission track dating and (U-Th)/He dating) to analysis of the tectonic evolution, sedimentary deposition and thermal history evolution of multi-cycle superimposed basin deeply by microscopic, inorganic isotopes dating of low-temperature thermochronology and trying to set up the model for deep marine hydrocarbon accumulation and redistribution in such basin, and hope to get some breakthrough in the theory and method for dynamic process analysis of tectonic and thermal evolution and deep marine oil and gas exploration.

海相油气近年来是我国油气勘查重点关注的领域之一。我国海相地层多赋存于多旋回叠合盆地、叠加盆地或残留盆地中，其深层海相油气勘探面临诸多问题和挑战，其中后期中、新生代构造运动的叠加、改造过程中，复杂的构造体制转换、构造叠加复合及热史控制下深层海相油气藏形成、改造和保存问题是困扰海相油气勘探的关键问题之一。 立项以中国南方典型的构造叠合盆地中扬子江汉平原区为例，在传统盆地分析和石油地质学研究的基础上，始终围绕叠合盆地构造-热演化动态过程及其对深层海相油气藏形成改造的控制作用这一科学问题，探讨利用国际新兴的低温热年代学定年技术，从微观、无机同位素低温热年代学角度剖析多旋回复合盆地构造、沉积及热史演化，探讨研究区内深层海相油气藏形成-改造模式。以期在叠合盆地构造-热史动态过程分析、深层海相油气勘探理论和方法有所突破，为该类型盆地构造-热史分析及油气勘探研究提供研究思路。

在传统地质研究的基础上，传统的地层对比和镜质体反射率可以确认中扬子江汉平原区存在燕山期和喜山期两次大规模的地层抬升剥蚀冷却事件。结合系统地构造-热年代学定年研究认为中扬子江汉平原区燕山期大规模抬升冷却事件发动时间是在早白垩世中后期(约135-110Ma)，而不是中晚侏罗。中、晚侏罗世-早白垩世初不仅没有发生大规模的构造抬升；相反，还有相当厚度的中-上侏罗统乃至下白垩统地层沉积。当阳复向斜和沉湖土地堂复向斜东部是主要沉积中心，沉积的中生代地层厚度最大>5000m；沉湖土地堂复向斜中部地区沉积厚度相对较小，约为1800-2600m。. 综合分析认为江汉平原区燕山期不是绝对的高热流或低热流，区内古热流分布极不均衡。当阳复向斜和沉湖土地堂复向斜东部古热流相对较低，平均在50-55mW/m2；沉沉湖土地堂复向斜古热流在~71mW/m2相对较高；当阳复向斜南部古热流最高，超过~80 mW/m2。研究认为当阳复向斜侏罗纪古地温平均在36.5-38.3℃/km左右；古近纪沉积时期平均古地温梯度为34.7℃/km。沉湖土地堂复向斜在侏罗纪至早白垩世抬升冷却前，古地温梯度在33.4℃/km~35.7℃/km之间；晚白垩世和古近纪逐渐降低，现今约为26℃/km。. 通过系统构造-热年代学研究认为，研究区发育1.浅埋加热-抬升冷却-深埋加热型；2.浅埋加热-抬升冷却-浅埋加热型；3.深埋加热-持续冷却-深埋加热型和4.深埋加热-后 期持续抬升冷却四种古地温演化模式。其中当阳复向斜属于深埋-抬升剥蚀-再深埋-抬升剥蚀，并在燕山期达到最大古地温，烃源岩成熟较早，烃源岩二次生烃的可能性较小，进一步的油气勘探应该以保存条件为主。而沉湖土地堂复向斜中部地区早期浅埋-抬升-深埋-小幅度抬升，上古生界烃源岩具有较强的二次生烃，研究区新生代断陷带周缘是上古生界海相地层二次生烃作用形成的油气藏成藏的有利靶区。