南海南部礼乐盆地礁体发育区的构造热演化特征  

Tectono-thermal evolution features of the reef body developing area in the Liyue Basin,southern South China Sea

作　　者：王丽芳 施小斌[3,4,5] 任自强 裴健翔[1,2] 杨小秋 谌永强 史德锋[1,2] 刘奎 赵鹏 闫安菊 WANG LiFang;SHI XiaoBin;REN ZiQiang;PEI JianXiang;YANG XiaoQiu;SHEN YongQiang;SHI DeFeng;LIU Kui;ZHAO Peng;YAN AnJu(Hainan Energy Ltd.of CNOOC,Haikou Hainan 570100,China;Zhanjiang Branch of CNOOC Ltd.,Zhanjiang Guangdong 524057,China;Key Laboratory of Ocean and Marginal Sea Geology,South China Sea Institute of Oceanology,Chinese Academy of Sciences,Guangzhou 510301,China;Innovation Academy of South China Sea Ecology and Environmental Engineering,Chinese Academy of Sciences,Guangzhou 510301,China;Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou),Guangzhou 510301,China;University of Chinese Academy of Science,Beijing 100049,China)

机构地区：[1]中海油海南能源有限公司,海南海口570100 [2]中海石油(中国)有限公司湛江分公司,广东湛江524057 [3]中国科学院边缘海与大洋地质重点实验室,南海海洋研究所,广州510301 [4]中国科学院南海生态环境工程创新研究院,广州510301 [5]南方海洋科学与工程广东省实验室,广州510301 [6]中国科学院大学,北京100049

出　　处：《地球物理学报》2020年第8期3050-3062,共13页Chinese Journal of Geophysics

基　　金：国家科技重大专项课题(2017ZX05026-005);国家自然科学基金项目(41776078);南方海洋科学与工程广东省实验室(广州)人才团队引进重大专项(GML2019ZD0104)资助.

摘　　要：礼乐滩是礼乐盆地的重要组成部分,自晚渐新世礼乐地块裂离北部陆缘后开始发育礁灰岩.为认识这些长期浸没海水中的礼乐礁体及其下伏地层的热状态与热演化特征,在详细分析礼乐滩钻井测温数据和镜质体反射率数据的基础上,对一条穿过礁体的骨干剖面进行了构造热演化数值模拟.结果显示,礁体区钻井2000~4500 m深度范围内温度介于30~90℃之间,井底与海底之间的平均地温梯度仅10℃·km^-1左右,地温梯度随深度逐渐增加,3000~4000 m深度段地温梯度介于32~37℃·km^-1;礁体下伏地层有机质曾经经历了比现今所处温度更高的古温度.进一步分析表明,高孔高渗的礁体上部因与周围低温海水发生热交换,导致地层温度降低、地温梯度和热流降低甚至为负值;与海水热交换作用随深度增加而减弱并最终停止,地层温度逐渐升高,地温梯度和热流值趋于正常;现今钻井3000~4000 m深度段地温梯度约为35℃·km^-1,基底热流可能介于65~75 mW·m^-2,平均约为70 mW·m^-2;礁体发育区有机质热成熟度主要是在礁体与周围低温海水发生实际热交换前获得的,礁体与海水热交换作用导致地层温度逐渐降低,有机质热成熟度增长缓慢,现今生烃门限深度明显大于邻近的北1凹陷中部区域的门限深度.Reed Bank is an important tectonic unit of the Liyue Basin,and has been developing reefs since drifting from the northern continent margin in the Late Oligocene.To understand the thermal state and thermal evolution features of these long term submerged reefs and underlying strata,we first made a detailed analyses on borehole temperature and vitrinite reflectance data,then modeled numerically the tectono-thermal evolution history of a typical profile just passing through a reef body of the Reed Bank.The results show that the borehole temperature in the depth interval of 2000~4500 m in the reef ranges from 30℃to 90℃,and the thermal gradient between the seafloor and the measured depth is only about 10℃·km^-1.The geothermal gradient increases gradually with depth,and the thermal gradient is about 32~37℃·km^-1 between 3000 and 4000 m.The maximum paleo-temperature that organic matter below the reef body has experienced should be much higher than their present environmental temperature.Further analyses suggests that due to heat exchange with the surrounding low temperature seawater,the upper part of the reefs with high porosity and high permeability is cooled,and seafloor thermal gradient and heat flow are greatly reduced,even to be negative.As the heat exchange with surrounding seawater became weak,and finally disappear with increasing depth,formation temperature gradually increases,and geothermal gradient and heat flow tend to be normal.The borehole geothermal gradient in the depth range of 3000~4000 m is about 35℃·km^-1,and the estimated heat flow across sedimentary basement is in the range of 65 and 75 mW·m^-2,with an average of 70 mW·m^-2.The organic matter maturity was mainly obtained just before the reefs began to exchange heat effectively with the surrounding low temperature seawater,and then with heat exchange between reef and seawater,thermal maturity of the organic matter has been increased slowly with decreasing formation temperature.As a result,the threshold depth of oil generation in the ree

关 键 词：礼乐滩 热状态 热史 热流 镜质体反射率 

分 类 号：P314[天文地球—固体地球物理学]