基于F⁃J法微动探测的表层结构调查

Surface structure survey by microtremor based on F⁃J method

三维地震勘探常常处于城镇、道路等无法实施微测井等静校正方法的区域,近期人们尝试利用微动调查替代现有的静校正方法,取得了一定效果。现今微动调查在石油勘探的应用中主要通过提取面波频散曲线反演地层速度结构。该方法在石油勘探领域仍处于起步阶段,作为核心技术的频散成像方法种类繁多,其中2019年提出的频率—贝塞尔变换法(Frequency‑Bessel,F‑J)受到人们的广泛关注。相比空间自相关方法(SPAC),F‑J方法在利用背景噪声高阶模式面波成像上具有巨大优势。为了更好地研究F‑J方法的适用性,首先利用合成数据分析了不同观测系统和采集参数对F‑J成像的影响;然后利用四川某地实际噪声数据分析了不同观测系统、采集时间对F‑J频散成像的影响。实际应用中采用分段择优叠加得到的频散谱,可有效提高频散谱成像质量,为准确提取频散曲线提供了数据基础。进一步对比测井数据,发现利用基阶、高阶模式频散曲线进行多模式联合反演可精确地反演地层结构,使经济、高效地获得表层结构成为可能。

3D seismic exploration is typically employed in areas where micro logging and other static correction methods cannot be implemented,such as towns and roads.Recently researchers have tried to replace existing static correction methods with microtremor surveys and yielded some achievements.At present,in petroleum exploration,microtremor survey mainly employs surface wave dispersion curves to invert formation velocity structures.This method is still in its infancy in petroleum exploration.As the core technology,dispersion imaging methods can be classfied into many types,such as the frequency‑Bessel(F‑J)transformation method proposed in 2019,which has attracted the attention of geophysicists.Compared with the spatial autocorrelation method(SPAC),the F‑J method has great advantages in adopting ambient noise for higher‑mode surface wave imaging.To better study the applicability of F‑J method,this paper first analyzes the influence of different observation systems and acquisition param‑eters on F‑J imaging using synthetic data.Then,the effect of different observation systems and acquisition time on FJ dispersion imaging is analyzed through the field ambient noise data of an area in Sichuan.In practical application,the dispersion spectrum obtained by subsection optimization superposition can effectively improve the imaging quality of the dispersion spectrum and provide a data basis for the accurate extraction of dispersion curves.Finally,logging data comparison shows that multi‑mode joint inversion using fundamental mode and higher‑mode dispersion curves can accurately invert formation structures,thus making it possible to obtain surface structures economically and efficiently.