基于正演模拟的奥陶系潜山岩溶储层地震响应特征——以塔里木盆地轮古地区为例

Study on Seismic Response Characteristics of Ordovician Buried Hill Karst Reservoir Based on Forward Modeling:Taking Lungu Area in the Tarim Basin as an Example

塔里木盆地北部轮古地区构造多期活动,形成复杂的断裂体系,增强了储层空间的复杂性;奥陶系潜山岩溶发育期次多,表层岩溶作用强烈;储层类型多,地震响应特征多样,纵横向变化大,埋藏深,储集体控制因素多,这些原因造成难以有效进行奥陶系潜山岩溶储层预测。针对塔北轮古奥陶系潜山岩溶储层预测难点,通过多口已钻井统计分析,选取较准确储层参数,设计3个模型,运用正演技术方法,开展了奥陶系潜山岩溶地震响应特征研究,以便指导奥陶系潜山岩溶储层预测。结果表明塔北轮古奥陶系潜山岩溶储层地震响应特征:串珠的大小随着洞穴的规模增大而增大;随着洞穴规模的增大,串珠的主频相应降低;潜山顶部发育串珠时,在潜山波阻抗界面处出现相位上移现象;在顶部发育洞穴时,潜山顶界面处表现为弱反射。随着洞穴距离潜山顶面距离的增大,串珠状反射逐渐下移,潜山顶面也逐渐由弱反射过渡为强波峰反射。随着纵向上2个洞穴间隔距离的增大,串珠间的干涉逐渐由相消干涉过度为相长干涉,串珠纵向延伸也相应增长。

Several tectonic movements were developed in the Lungu area of Tabei,forming a complex fault system,which also led to a complex reservoir space system.Several stages of karstification were confirmed in the Ordovician buried hill karst with strong epikarst karstification.Reservoirs were characterized by various types of reservoirs,variable characteristics in seismic response,large changes in vertical and lateral,deep buried depth,and various controlling factors on the reservoir bodies.All these characteristics caused a lot of difficulties in reservoir prediction for reservoirs of Ordovician buried hill.Aiming difficulties in reservoir prediction,selected relatively accurate reservoir parameters to design three models by forwards technique according to statistical analysis of several drilled wells.Study on seismic response characteristics in Ordovician buried hill karst has been carried out to guide the prediction of reservoirs in Ordovician buried hill karst.According to the study results,seismic response characteristics of reservoirs in Ordovician buried hill karst of Lungu area were listed as below:The size of'string'reflection increased along with the increasing cave scales;with the increase of cave scales,the main frequency of the'string'reflection will decrease correspondingly;when'string'reflection was developed in the top of buried hill,the upward-shift of phase can be found in the wave-impedance surface of buried hill;while cave was developed in the top,weak reflection can be found in the top-surface of the buried hill.Along the increasing distance between the cave and top-surface of the buried hill,'string'reflection will move downwards gradually,and the weak reflection in the top of buried hill will transfer to strong wave-peak gradually.With the increase of distance between two caves in vertical,coherent interference between'string'reflections transfer to subtraction interference gradually,and vertical elongating also increases correspondingly.