北部湾盆地海中凹陷地层特征地震识别研究

北部湾盆地多期构造演化及沉积沉降中心迁移,使得不同凹陷存在沉积差异,由于缺乏钻井资料,海中凹陷地层结构研究及盆地主要烃源岩层流沙港组二段(流二段)预测均十分困难。依托三维地震资料联片处理,基于层位标定及初步建立的构造框架模型,运用地震相类比、地震属性和测井约束反演等技术,由定性类比到定量分析,对北部湾盆地涠西南凹陷及海中凹陷沉积地层进行了地震识别研究。研究认为海中凹陷与涠西南凹陷流沙港组二段、流沙港组三段(流三段)地震相、均方根振幅及波阻抗等属性的变化具有对应层段高度相似的特点,据此类比建立海中凹陷地层建造,查明该凹陷流二段、流三段地层分布特征。结果表明,海中凹陷与涠西南凹陷古近系地层特征相似,流沙港组具相同沉积演化过程,海中凹陷流三段为水动力条件较强的砂泥岩互层沉积,流二段与涠西南凹陷完全一样,发育相对稳定的湖相泥岩相沉积,即存在良好的烃源岩条件。此认识与HZ2井钻井结果吻合,表明该凹陷具有良好的油气前景,为下一步油气勘探提供了科学依据。

Because of the multi period tectonic evolutions and the migration of sedimentary center and subsidence center in Beibu Gulf Basin,the stratum structure of the Haizhong Sag without adequate drilling wells data is fuzzy and there are different understandings on the existence of hydrocarbon source rocks (The 2nd member of Liushagang formation).In order to solve the problem,based on the drilling horizon calibration and preliminary establishment of structural frame model,3D seismic data were used to identify the formations of Weixinan Sag and Haizhong Sag in the North depression of Beibu Gulf Basin by several seismic techniques such as seismic facies analogy,quantitative seismic attribute analysis and logging constrained inversion.The seismic facies,RMS amplitude and acoustic impedance from the 2nd and 3rd member of Liushagang formation in Weixinan Sag and Haizhong Sag have been studied from qualitative analogy to quantitative analysis.The study finds above three seismic attributes from  the target formations in the two sags  have highly similar characteristics for the corresponding layers.So the formation distribution of Haizhong Sag has been further defined,especially the 2nd and 3rd member of Liushagang formation.Research results show that Haizhong Sag has the same stratum with Weixinan Sag.The two sags have similar sedimentary evolution in Liushagang period,the 3rd member of Liushagang in Haizhong Sag is sand and mudstone interaction deposition in strong hydrodynamic condition and the 2nd member of Liushagang is lacustrine mudstone deposition in relatively stable environment which is the same to Weixinan Sag.So there was good hydrocarbon rock condition in Haizhong Sag.The above understanding was confirmed by HZ2 wells and it indicates that Haizhong Sag has good prospects for hydrocarbon exploration,which provides a scientific basis for the next step hydrocarbon exploration.

中国石油化工股份有限公司项目(P14088)资助。