北海盆地维京地堑渐新统砂岩侵入体形态特征及成因

摘要

Sandstone intrusions are a common class of soft-sediment deformation. They are formed by the forceful in-trusion of fluidization sand into overlying sealing sequence during early stages of burial. Based on 3-D high-resolution seismic data and logging data, we utilize methods of seismic reflection configuration analysis and coherence cube slice to illustrate geometry and induced mechanism of sandstone intrusions. Results indicated that sand intrusions appear V-shaped or W-shaped high amplitude anomalies in seismic sections;conical bodies are 1-2 km on the plane and up to hundreds of meters high;fluid emplacement and polygonal fault systems inducing cap-rock fracture are the key factors for overpressure of depositional sand body and fluidization of sand. After injection, sandstone intrusions may serve as high-permeability fluid flow passage for a long term and has great significance for vertical migration of fluid. More im-portantly, sandstone intrusions may serve as favorable reservoirs. So it has a great guiding significance to evaluation of cap-rock sealing capacity and hydrocarbon exploration.%砂岩侵入体是由处于浅埋藏阶段、尚未固结的砂质沉积物发生液化并侵入到上覆盖层所形成的一类软沉积物变形,在北海盆地维京地堑渐新统地层中非常发育.为探讨砂岩侵入体的形态特征及诱发机制,通过高分辨率三维地震及测井资料,利用地震反射结构分析、地震相干切片等手段对砂岩侵入现象进行了识别;并结合多边形断层系统、流体充注与砂岩侵入之间的关联性,对砂岩侵入体的成因机制进行了分析.结果表明:在地震剖面上可识别的砂岩侵入体多呈V型或W型强振幅反射特征,其横向展布规模约1~2 km,垂向侵入高度约100~200 m;流体的大规模充注及多边形断层诱发盖层破裂是形成砂体内部超压并诱发其发生液化的关键因素.砂岩侵入体在形成之后可以作为流体运移通道,对强化流体的垂向运移具有重要意义;并且砂岩侵入体本身即可作为油气的有利储集体.因此识别并分析砂岩侵入体的成因机理,对盖层封闭性评价及油气勘探具有重要指导意义.