克拉通内盆地走滑断层地震判识的若干陷阱

Pitfalls in seismic identification of strike-slip faults in intracraton basin

1.西南石油大学地球科学与技术学院,四川成都 610500;
2.中国石油西南油气田公司勘探开发研究院,四川成都 610051;
3.西南石油大学天然气地质四川省重点实验室,四川成都 610500;
4.中国石油塔里木油田公司,新疆库尔勒 841000

1. School of Geoscience and Technology,Southwest Petroleum University,Chengdu 610500,China;
2. Exploration and Development Research Institute,PetroChina Southwest Oil & Gasfield Company,Chengdu 610051,China;
3. Sichuan Key Laboratory of Natural Gas Geology,Southwest Petroleum University,Chengdu 610500,China;
4. PetroChina Tarim Oilfield Company,Korla 841000,China

克拉通盆地内走滑断层位移量小、变形微弱且构造复杂,深层地震低分辨率识别走滑断层困难且受诸多假象影响。通过剖析塔里木和四川盆地克拉通内走滑断层的典型地震现象,结合地质因素综合分析辨别走滑断层是否发育,总结了典型的地震假象并建立三大类陷阱模式,主要包括:①基底陡崖、阶梯状断裂与断垒结构可能误判为“花状构造”,基底盖层垂向发育的相似褶皱也可能成为走滑构造假象;②喷发岩、蒸发岩厚度、岩性的横向变化,可能造成地震层速度横向突变,导致下伏岩体在地震剖面上产生似走滑断层的高陡假象;③垂向规模发育的沟谷地形、岩溶地貌、岩相相变等地质现象可能出现似走滑断层的地震响应。为避免这些地震解释陷阱,在提高走滑断层地震分辨率的基础上,排除蒸发岩和火成岩的速度影响,剔除地形地貌与岩相变化的影响,并基于以地震平面属性为主的典型走滑构造识别,排除地震走滑断层的假象,建立合理的走滑断层地震地质解释模式。

It is challenging to identify strike-slip faults in a Craton basin owing to their small displacement,small deformation,and complicated tectonic features,particularly in the context of low seismic resolution and false images in deep zones.According to typical seismic signatures of intracraton strike-slip faults in the Tarim and Sichuan Basins and geologic factors,we identify misconceptions of seismic interpretation and extract three pitfalls.The first is that precipitous cliffs at basement,step-like fractures,and faulted horsts may be misinterpreted as flower structures;similar folds occurring vertically between the basement and overburden may be treated as strike-slip structures by mistake.The second is false images of underlying rock masses as steeply dipping strike-slip faults on seismic sections caused by the occurrence of eruptive rocks and evaporites with lateral thickness and lithology variations,leading to sudden interval velocity change laterally.The third is strike-slip fault-like responses related to some geologic phenomena,e.g.large vertical ravines,karst landform,and lithofacies change.To avoid these pitfalls,the impacts of evaporite and igneous-rock velocities,landform,and lithofacies should be mitigated in enhanced-resolution seismic data interpretation.Seismic attribute maps are the top selection for strike-slip fault identification to exclude false images of strike-slip faults on seismic sections and establish a correct model for seismic-geologic interpretation of strike-slip faults.

中国石油—西南石油大学创新联合体科技合作项目(2020CX010101)资助。

10.12431/issn.1000-1441.2024.63.04.015