查干凹陷构造-热演化研究

Tectono – thermal evolution is one of the basic and difficult issues on the basin analysis and Petroleum Geology. In the grim situation, our traditional large oil fields facing cuts and oil consumption increasing, it is urgent to look for replacing oil and gas area. Zhongyuan Oilfield, SINOPEC is focusing on oil and gas exploration in the Chagan sag of the Yingen-Ejinaqi basin, Inner Mongolia. More than 0.5 × 108 tons of petroleum reserves and two new oilfields (i.e., Jixiang and Ruyi oilfields) have been discovered in the Chagan sag by 2013. The discoveries indicate that the Chagan sag is a promising exploration area. However, as one of important and basis works of the oil and gas resource assessment and exploration, the thermal history has some issues, including few and no system thermal indicator data and denudation unclear in the critical geologic periods, which makes it difficult to recover the thermal history of the Chagan sag. This leads to different understanding of geologic period of main hydrocarbon generation and end of hydrocarbon generation, thereby affecting the correct understanding of the law of oil and gas accumulation, which has restricted the petroleum exploration. Therefore, the project is applied, and intends to systematically measure apatite fission track, apatite (U-Th)/He and vitrinite reflectance of organic matter for the typical wells at first, and then determine the tectono-thermal evolution histories of the Chagan sag using positive and inversion combining methods on basis of the above thermal indicators. The results can provide important scientific basis for a correct understanding of hydrocarbon accumulation and its evolution and petroleum resources assessment of the Chagan sag.

构造-热演化是盆地分析和石油地质学领域的基础和难点问题之一。在我国传统的大型油田都面临着减产、油气消耗日渐增加的严峻情势下，急需寻找油气接替区。中国石化中原油田重点对内蒙古银-额盆地查干凹陷进行油气勘探。截至2013年底，已发现石油储量5000余万吨，建立了吉祥和如意两个油田，证实查干凹陷具有较好的勘探前景。但是作为油气资源评价及勘探中重要的、基础的工作之一的热历史的研究存在古温标少，且不系统和关键地质时期的剥蚀量不清楚等问题，难于恢复该凹陷的热历史，导致该凹陷烃源岩主生烃期和生烃结束的地质时间认识不一，进而影响对油气成藏规律的正确认识，这已经制约着油气的勘探。因此，申请该项目，拟通过系统测试典型井的磷灰石裂变径迹、磷灰石(U-Th)/He和镜质体反射率，采用正、反演相结合的方法厘定查干凹陷的构造-热历史。研究结果可以为正确认识查干凹陷油气成藏及其演化和油气资源评价提供重要科学依据。

在我国传统的大型油田都面临着减产、油气消耗日渐增加的严峻情势下，急需寻找油气接替区。中国石化中原油田重点对内蒙古银-额盆地查干凹陷进行油气勘探，勘探已经证实该凹陷具有较好的勘探前景。但是作为油气资源评价及勘探中重要的、基础的工作之一的热历史的研究存在古温标少、且不系统等问题，难于恢复该凹陷的热历史，导致该凹陷烃源岩主生烃期和生烃结束的地质时间认识不一，进而影响对油气成藏规律的正确认识，这已经制约着油气的勘探。因此，在该背景下申请了该项目，通过测试获取典型井的系统稳态测温数据、测试样品的岩石热导率和生热率，对查干凹陷的现今地温场进行了研究；同时，测试典型井的磷灰石裂变径迹和镜质体反射率，利用采用多温标耦合反演相结合的构造-热演化研究方法厘定了查干凹陷的构造-热历史。研究中获得了如下关键的数据：(1)通过对祥2、祥5、意5和意7井进行了系统稳态测温，共获得148个系统测温数据，这是银-额盆地第一批稳态系统测温数据；(2)测试了21口井178块样品的岩石热导率和18口井99块样品的生热率，为搞清该凹陷的热物理参数及热史恢复提供基础数据；(3)测试了14口35个磷灰石裂变径迹和15口119个镜质体反射率，为多温标耦合反演提供古温标数据。研究结果表明：(1)查干凹陷平均地温梯度及大地热流为32.2℃/km和70.5mW/m2(这是银额盆地第一批大地热流数据)，揭示出该凹陷具有构造稳定区和构造活动区之间的中温型地温场特征；(2)构造-热演化恢复结果显示查干凹陷白垩系具有高的地热状态，并且该凹陷经历了地温梯度快速增加阶段(K1b-K1s)，地温梯度高峰阶段(K1y)，高地温延续阶段(K2w)和热沉降阶段(Cz)四个构造-热演化阶段。同时，通过该项目的研究，总结得出了断陷盆地热体制及油气资源评价方法体系，并在银额盆地拐子湖凹陷、二连盆地白音查干凹陷、乌里雅斯太凹陷、东濮凹陷和南祁连盆地得到了很好的应用。