沉积盆地盐构造热效应及其油气地质意义  

Geothermal effects of salt structures on marine sedimentary basins and implications for hydrocarbon thermal evolution

作　　者：刘绍文[1] 杨小秋[2] 邱楠生[3] 杨树春[4] 李旭东[1] LIU ShaoWen YANG XiaoQiu QIU NanSheng YANG ShuChun LI XuDong(Key Laboratory of Coast and Island Development, School of Geographic and Oceanographic Sciences, Nanjing University, Nanjing 210023, China z Key Laboratory of Marginal Sea Geology, South China Sea Institute of Oceanology, China Academy Sciences, Guangzhou 510301, Chin State Key Laboratory of Petroleum Resources and Prospecting, China Petroleum University, Beijing 102249, China Research Institute of China National Offshore Oil Corp. （CNOOC）, Beijing 100027, China)

机构地区：[1]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,南京210023 [2]中国科学院南海海洋研究所,边缘海地质重点实验室,广州510301 [3]中国石油大学(北京)油气资源与探测国家重点实验室,北京102249 [4]中海石油(中国)有限公司北京研究中心,北京100027

出　　处：《科学通报》2017年第15期1631-1644,1551,共14页Chinese Science Bulletin

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

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.Evaporitic salt is prevalent in marine sedimentary basins, and many discovered hydrocarbon reservoirs are generally associated with salt structures in the world; accordingly salt structures have attracted much attention from academia and industry during the past decade. The Tarim Basin, located in northwest China, is the largest marine sedimentary basin in China with great hydrocarbon resource potential. Previous studies of salt structures in this basin mainly focused on its strong sealing capacity and structural traps created by salt structures. However, besides its extreme impermeability and low viscosity, rock salt has other unique thermal properties, including a large thermal conductivity as high as 5-6 W/（m K）, usually 2-3 times greater than that of other common sedimentary rocks, but a relatively low radiogenic heat production. This strong contrast in thermal properties could change the evolving thermal regime and associated thermal history of the source rocks around salt bodies, but it has not been understood well. Herein based on the theoretical models and interpreted salt-bearing seismic profiles from the Kuqa Foreland Basin, northern Tarim Basin, we use 2D finite element numerical experiments to investigate the impacts of salt structures on the basin geothermal regime and associated hydrocarbon thermal evolution. Our results show that, owing to their high efficiency in heat conduction, the salt rocks would result in obviously positive temperature anomalies （3%-13%） above the salt body and negative temperature anomalies （11%-35%） in the subsalt, enhancing and restraining the thermal maturation of source rocks above and below the salt body, respectively. The amplitude and extent of geothermal effects of salt structures depend on the thermal conductivity, geometry, thickness and burial depth of the salt bodies. The thermally affected area around the salt body can be 2 times the salt radius laterally and 2-3 times the salt thickness vertically. Salt structures in the Kuqa Foreland Basin can prom

关 键 词：盐构造 地温梯度 热物性 热演化 库车前陆盆地 

分 类 号：P618.13[天文地球—矿床学]