摘要:
川西坳陷海相勘探目的层埋藏较深,反射资料频带窄,地震分辨率无法满足勘探要求,地层吸收衰减是导致分辨率低的主要原因,为了解深层地震波的衰减情况,首先根据低降速带资料和测井资料建立川西坳陷地层模型,然后定量估算球面扩散、吸收衰减和透射损失引起的地震波衰减量,以估算的衰减值为参考,同时结合地震采集资料、井中零偏VSP和Walkway-VSP资料来分析影响深层反射波高频信号接收的因素。分析指出1500m以上浅层强吸收衰减是造成川西坳陷深层反射波高频成分缺失的主要原因,5000m以下海相地层反射波频带只能达到40 Hz左右,深层资料采集应以降低背景干扰为重点,并在提高资料采集密度上下功夫,以达到增强深层弱反射信号、提高地震勘探精度的目的,而不应单纯强调提高分辨率。
Abstract:
InwesternSichuanbasindepression,themarinefaciestargetlayersareburiedingreatdepth,resultinginnarrowfrequency bandofreflectedseismicdata.Henceseiemicresolutioncannotmeettheneedofprospectinggoals,andlowseismicresolutionisre-sponsibleforstratigraphicabsorptionattenuation.Inordertounderstandcompletelythereasonfortheattenuationofseismicwaves,the authorsbuiltamodelforwesternSichuanbasindepressionstrata,thencalculatedquantitativelysphericaldivergence,absorptionand transmissionattenuationofseismicwavebasedonthemodel,andcombinedthecalculatedattenuationvalueswithseismicdata,VSP andWalkway-VSPdatatoanalyzethefactorsaffectinghighfrequencyreflectedsignalacquisitionrecordingofdeeplayers.Itturnsout thattheseriousabsorptionattenuationofshallowstrataabove1500metersisthefundamentalcauseresponsibleforhighfrequencycom-ponentlossesofdeeplayersinwesternSichuanbasindepressionand,asforthemarinefaciestargetlayersburieddeeperthan5000me-ters,fieldacquisitiondatacanonlyreachabout40Hzfrequencyband.Therefore,thefieldacquisitionmethodsaimingatdeeptarget layersshouldfocusonreducingbackgroundnoisesandincreasingacquisitiondensitytoenhanceweakreflectionsignalsofdeeplayers soastoimprovetheseismicprospectingprecision,ratherthansolelyfocusonimprovingtheseismicresolution.
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