沉积盆地盐构造热效应及其油气地质意义

发布时间：2018-10-12 06:41

【摘要】：海相沉积盆地广为发育盐岩,盆内油气藏多与盐岩有关.塔里木盆地是中国最大的海相沉积盆地,该区以往的盐构造研究主要集中于其作为良好盖层的封堵性能和作为构造圈闭的盐相关构造.实测表明,盐岩热导率远大于普通沉积岩(约2~3倍),盐岩这一强烈的热物性差异必然会对盆地地层温度分布及烃源岩热演化产生显著影响,但该问题尚未引起重视.本文基于系列理论模型和库车前陆盆地盐构造地震解释剖面,采用二维有限元数值模拟实验,定量探讨了盐构造的热效应及其对烃源岩热演化的影响.研究表明,盐体会造成盐上地层显著增温(3%~13%)和盐下地层降温(11%~35%),进而分别加速盐上烃源岩和抑制盐下烃源岩的热演化过程.盐体的热导率、几何形态、厚度和埋深是控制地热异常幅度的主要因素.异常范围与盐体尺寸有关,横向上可达盐体宽度的2倍、垂向上为盐体厚度的2~3倍.盐构造使得库车前陆盆地盐下地层温度显著降低,造成盐下侏罗系烃源岩镜质体反射率(Ro)降低约18%,从而有利于盐下深层油气的保存.库车前陆盆地东、西部的盐构造在埋深、厚度、成分和构造变形样式等方面均存差异,这可能是造成该区中生界烃源岩有机质成熟度时空差异分布的原因.上述盐构造的热效应对中国海相沉积盆地深层油气资源潜力评价与勘探具有重要意义.
[Abstract]:Salt rocks are widely developed in marine sedimentary basins, most of which are related to salt rocks. The Tarim Basin is the largest marine sedimentary basin in China. The previous studies of salt structure in this area mainly focus on its plugging performance as a good caprock and salt-related structure as a structural trap. The measured results show that the thermal conductivity of salt rock is much higher than that of common sedimentary rock (about 2 ~ 3 times). The strong difference in thermal properties of salt rock will inevitably have a significant impact on the formation temperature distribution and thermal evolution of source rock in the basin, but this problem has not been paid much attention to. Based on a series of theoretical models and seismic interpretation profiles of salt structures in Kuqa Foreland basin, the thermal effects of salt structures and their effects on the thermal evolution of hydrocarbon source rocks are quantitatively discussed by using two-dimensional finite element numerical simulation experiments. The results show that salt experience can significantly increase the temperature of the upper salt formation (313%) and lower the temperature of the subsalt formation (1135%), thus accelerating the thermal evolution of the source rock and restraining the thermal evolution of the subsalt source rock, respectively. The thermal conductivity, geometry, thickness and depth of salt are the main factors controlling the amplitude of geothermal anomaly. The anomalous range is related to the size of salt body, which can reach 2 times of the width of salt body laterally and 3 times of the thickness of salt body vertically. The salt structure makes the subsalt formation temperature of Kuqa Foreland basin significantly lower, resulting in the reduction of vitrinite reflectance (Ro) of the source rocks of the Lower Salt Jurassic by about 18%, which is beneficial to the preservation of deep oil and gas under salt. The salt structures in the east and west of Kuqa Foreland basin are different in depth, thickness, composition and structural deformation pattern, which may be the reason for the spatial and temporal distribution of organic matter maturity of Mesozoic source rocks in this area. The thermal effects of the above salt structures are of great significance to the evaluation and exploration of the deep oil and gas resources potential of marine sedimentary basins in China.
【作者单位】：南京大学地理与海洋科学学院海岸与海岛开发教育部重点实验室;中国科学院南海海洋研究所边缘海地质重点实验室;中国石油大学(北京)油气资源与探测国家重点实验室;中海石油(中国)有限公司北京研究中心;
【基金】：国家自然科学基金(41272143,41106086) 中国石油科技创新基金(2015D-0506-0105)资助
【分类号】：P618.13

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