塔里木盆地褶皱中和面与油气成藏关系初探

The Relationship between Fold Neutral Planes and Hydrocarbon Accumulation in Tarim Basin

塔里木盆地从前震旦纪至今主要有七个演化阶段,其中的三次前陆盆地阶段是形成褶皱中和面的主要时期。古油藏能否保存下来,实际上要看褶皱中和面是否能被保存完整。在遭受很大剥蚀的古生界构造,虽然残存的构造核部仍保存有较大的地质空间,但易于聚集油气的背斜上中和面(TA)地层不太容易被保存下来。塔里木盆地Fang1构造,其背斜上中和面TA地层已基本被剥蚀殆尽,只有一小部分残留,Fang1井因钻在背斜下中和面(CA)部位而钻探失败。主要原因是CA部位是构造挤压区,属油气排出区。Tadong3构造区背斜中和面以上部位也已遭受剥蚀,残留的背斜下中和面看上去仍为背斜构造,但已属于构造应力挤压区,为不能储集油气的CA区,因此对该构造的勘探风险很大。对塔里木盆地古生界,需要寻找较完整的或剥蚀不大的背斜上中和面构造油藏;对中—新生界,除了寻找发育较完整的上中和面构造外,还应重视向斜下中和面部位的构造或岩性油气藏。

Preservation of a fossil oil reservoir is actually decided to whether the fold neutral plane keeps entirely or not. In Tarim Basin, although the residual cores of Palaeozic anticlines that are greatly denuded still have large geo- logical space, the strata located at the upper neutral plane （UNP） which are favorable to hydrocarbon accumulation could not been preserved easily. The cause of drill failures in Fang-1 and Tadong-3 anticlines is analyzed as cases. In these anticlines, the UNP strata are mostly denuded and only a small part of it is remained. The reason of drill failures is that either well was just drilled to the lower neutral plane（LNP） which belongs to the hydrocarbon-drain- ing area under tectonic compression stress. Therefore, drill risks will be faced to alike anticlines. It is necessary to look for the Paleozoic reservoirs at UNP in anticlines where the strata are less denuded. Besides, an attention should be paid to the Meso-Cenozoic structural and/or lithological reservoirs at LNP in synclines.