孟加拉湾若开海域晚新生代构造变形及其对油气的控制作用

摘要

Based on recent drilling and 2D/3D seismic data, the late Cenozoic deformation of Arakan fold belt and its control on hydrocarbon accumulation was investigated in offshore Rahkine, Bay of Bengal. The analysis result shows that only a basal detachment fault (10km of burial depth) develops in the southern part of the study area while a basal detachment fault (12km deep buried) and a middle detachment fault (4km deep) develop in the northern part. Under the control of these detachment faults, one set of tectonic layers develops in the southern part and two sets of layers (the upper and the lower one) in the northern part, respectively. The lateral extended distance, the wave length and the interval distance between anticlines are longer obviously in the southern part than those in the northern part. In addition, both the NS-trending anticline and the secondary NE-trending transtensional dextral strike-slip fault formed in the up-per tectonic layer in northern part. According to growth strata records, these deformations formed in late Quaternary and at the end of late Quaternary respectively. Trap formation, hydrocarbon migration and accumulation conditions are greatly controlled by the late Cenozoic deformation. It is suggested that the structural-lithologic composite traps have the condition to form large gas fields in the gentle fold belt and the southern part of the study area is the favorable ex-ploration targets in the future.%利用钻井、二维和三维地震资料，剖析了孟加拉湾若开海域晚新生代的构造变形特征，探讨了构造变形对油气的控制作用。区域深度地质剖面揭示，研究区南部仅发育底部滑脱层(深度10 km)，而北部则发育底部滑脱层(深度12 km)和中部滑脱层(深度4 km)；受滑脱层的控制，研究区南部仅发育一套构造层，而北部则发育变形不协调的上、下两套构造层；南部背斜的南北向延伸距离、波长及背斜间隔距离均明显大于北部。通过北部局部构造精细解析表明，研究区北部变形相对较复杂，上构造层主要发育近南北向的背斜和次级张扭性右旋走滑断层，二者形成时间分别为晚第四纪和晚第四纪末。若开海域晚新生代的构造变形对圈闭形成、油气运聚和保存条件具有重要的控制作用。指出研究区南部平缓褶皱带构造—岩性复合圈闭具备形成大油气田的条件，是下一步油气勘探的重要目标。