针对四川盆地龙门山推覆构造复杂地质目标的地震采集技术

Seismic acquisition for complex geologic targets, nappe structure of Longmenshan Mountain

近年在四川盆地西北部龙门山山前隐伏带钻探的多口井在二叠系获得了高产工业气流,但是该区块的地表地形起伏剧烈,出露地层复杂,涉及石灰岩、砂泥岩、砾岩、河滩砾石等多种岩性,激发接收条件差,且地腹地质结构复杂,断裂发育、地层倾角大,甚至直立倒转,导致有效地震波能量极弱,地震波成像效果差,难以获得目的层的有效反射,无法满足油气勘探需求。为获得更好的地震采集资料,特别是推覆构造带的中、深层地震信息,针对该区块开展了地震采集攻关,采用高覆盖三维观测设计、激发及接收条件优选、过障碍动态观测系统设计等技术措施,保证了目的层有效波覆盖次数,提高了采集单炮的信噪比,改善了复杂构造成像效果,整体上剖面成像效果得到大幅提升。

In the piedmont buried belt of Longmenshan Mountain,northwestern Sichuan Basin,high-yield industrial gas flow has been obtained from the Permian in some wells.This block,however,is featured by salient surface topographic relief,complex exposure strata which are composed of limestone,sand shale,conglomerate,and bench gravel,bringing about poor exciting and receiving conditions.In addition,with complex structure and developed faults,the belly in this block is characterized by high stratigraphic dip even vertical reversal,resulting in weaker energy of seismic wave and poorer imaging effect of seismic wave.It's very hard to achieve the effective reflection of the target and to meet the exploration demand.So,Many acquisition technologies and measures,including high-coverage 3D survey design,exciting-and receiving-condition optimization,and dynamic obstacle-crossing geometry design,were studied and made in order to acquire better seismic data especially on middle to deep layers of Longmengshan nappe belt.These technologies and measures may ensure the coverage frequency of effective wave in the target,increase the signal-to-noise ratio of single-shot acquisition,perfect the imaging effect of complex structure,and greatly improve the imaging effect of section.