泌阳凹陷下二门油田油气成藏机理研究

Study on Reservoir-forming Mechanism in Xiaermen Oilfield , Biyang Depression

下二门油田位于泌阳凹陷东部边界下降盘内侧,是一个在早期同沉积逆牵引背斜构造基础上后期通过差异抬升和断裂改造的背斜构造。该油田油气差异聚集特征明显,从核三段和核二段下部的纯油藏,向上过渡到核二段上部带气顶的油藏,直到核一段和廖庄组为纯气藏,油源对比表明其上部的油气是通过长距离垂向运移由下部成熟油气向上运移聚集的。下二门背斜是一个早期(核三段Ⅶ砂组沉积时期)伴随着边界断裂的快速下降而形成的同沉积逆牵引背斜构造,但隆起幅度不明显,早喜马拉雅运动(廖庄组沉积末期)使该区遭受强烈的挤压,形成从下到上幅度逐渐加大的背斜隆起,晚喜马拉雅运动,形成北东、北东东向的张性断裂,使下二门背斜构造断裂化,形成了现今与断层有关的多种圈闭类型。与其相对应地该油田具有多期成藏和调整成藏的特点,一是发生在核一段沉积末期古油藏形成时期,二是发生在廖庄组沉积末期古油藏遭受破坏和成熟油气开始大量充注的时期,三是发生在廖庄末构造抬升期的晚期和第四系沉积前的大量油气充注和现今油气藏定型时期。其油气成藏模式是早期通过单砂体运移通道侧向运移缓慢充注聚集,中后期廖庄组末期差异抬升运动导致势能差的急剧增大而快速充注和断裂改造垂向调整运移聚集成藏模式。

There are clear hydrocarbon accumulation features for Xiaermen Oilfield in Biyang Depression of Nanxiang Basin, which changed upward from pure reservoirs in Member He3 and He2 to reservoirs with gas cap in the upper part of Member He2, and up to pure gas reservoirs in Member He1 and Liaozhuang. Oil-source correlation shows that hydrocarbon in the upper part migrated and accumulated upward through long distance vertical migration from the lower mature gas-oil. Along with fast drawdown of boundary fracture during deposition of sand group VI in Member He3, Xiaermen anticline structure came into being antithetic drag anticline structure together with deposition, but lifting amplitude is not clear. This area was subjected to strong compression caused by early Himalayas movement （ at the deposition last term of Liaozhuang Member）, this caused Xiaermen ancline structure into fracture developing many trap types connected with faults. Correspondingly, this oilfield is characterized of multi-term reservoir-forming and modified reservoir-forming： （ 1 ） reservoir-forming took place in the paleo-reservoir-forming period at the position last term of Member Her; （2） reservoir-forming took of mature oil-gas at the deposition last term place in the period of destruction of paleo-reservoir and began the filling of Member Liaozhuang; （3） reservoir-forming took place at the end of structure-rifting period in the late deposition, enough oil-gas filling before the Quaternary deposition. Hydrocarbon reservoir forming modes are that hydrocarbon laterally migrates through channels in single sand body and slowly fill and accumulate in the early term, and during mid and last term hydrocarbon fast migrate, fill and accumulate into reservoir because of sharp increase in potential energy caused by differential lifting motion, and vertical fracture modification at the end of Liangzhuang deposition period.