HTI煤层方位AVO响应与裂隙识别  

Analysis of azimuthal AVO response and crack identification on HTI tectonic coal

作　　者：李勤[1] 王玮 马随波 赵斌 LI Qin;WANG Wei;MA SuiBo;ZHAO Bin(College of Geology and Environment,Xi’an University of Science and Technology,Xi’an 710054,China)

机构地区：[1]西安科技大学地质与环境学院,西安710054

出　　处：《地球物理学进展》2021年第1期178-186,共9页Progress in Geophysics

基　　金：国家自然科学基金项目(41674135,41304105)资助。

摘　　要：煤层在顶板压实作用下水平裂隙近乎闭合,多垂向裂隙发育,因此将该类煤层等效为HTI介质,研究裂隙密度和填充物类型对方位AVO的影响,可以为预测裂隙提供理论依据,对煤田勘探有重要意义.本文基于Thomsen各向异性理论和模型等效理论建立上层为各向同性介质而下层为垂向裂隙发育的HTI煤层的正演模型,推导出适用于所建模型的更高精度反射系数近似公式对不同裂隙密度、不同填充物类型的模型进行方位AVO数值模拟,并利用反射系数进行地震记录合成;从反射系数空间曲面和地震记录两方面分析不同模型随着入射角、方位角、裂隙密度、裂隙填充物的改变而产生的不同地震响应.结果表明:裂隙密度的增大导致反射系数空间曲面波幅增大,地震记录波振幅增大;裂隙密度相同时,饱和水裂隙模型和干裂隙模型的反射系数空间曲面和合成地震记录存在显著差异;方位角为0°时,饱和水裂隙模型和干裂隙模型的反射系数差值达到0.2,分辨性较强;在方位角为0°时,入射角大于45°时地震记录差异最显著.测试数据中,含饱和水裂隙煤层的反射系数绝对值低于干裂隙煤层,地震记录的振幅也低于干裂隙煤层.Under the action of roof compaction, the horizontal fissures of coal seams are nearly closed and many vertical fissures are developed. Therefore, equivalent to HTI medium, studying the influence of fissure density and filler type on azimuthal AVO can provide theoretical basis for predicting fissures and is of great significance to coal exploration. In this paper, based on Thomsen anisotropy theory and model equivalence theory, a forward model of HTI coal seam with isotropic medium in the upper layer and vertical fractures in the lower layer is established. Azimuthal AVO numerical simulation is carried out for models with different fracture densities and different filler types by adopting azimuthal AVO approximation formula suitable for the established model, and seismic record synthesis is carried out by using reflection coefficient. The different seismic responses of different models with the changes of incident angle, azimuth angle, fracture density and fracture filler are analyzed from the reflection coefficient space curved surface and seismic records. The results show that the increase of fracture density results in the increase of the amplitude of reflection coefficient spatial curved surface and the amplitude of seismic record. When fracture density is the same, there are significant differences between saturated water fracture model and dry fracture model in reflection coefficient space curved surface and synthetic seismic record. When the azimuth angle is 0°, the difference between the reflection coefficients of the saturated water fracture model and the dry fracture model reaches 0.2, with strong resolution. When the azimuth angle is 0°, the difference in seismic records is most significant when the incident angle is greater than 45°. In the test data, the absolute value of reflection coefficient of fractured coal seam with saturated water is lower than that of dry fractured coal seam, and the amplitude of seismic records is also lower than that of dry fractured coal seam.

关 键 词：方位AVO 裂隙密度 HTI介质 反射系数 

分 类 号：P631[天文地球—地质矿产勘探]