利用地震波形—振幅响应技术预测海相碎屑岩岩性组合——以北康盆地为例

Prediction of marine clastic rocks assemblage with seismic waveform and amplitude responses:an example in Beikang Basin,South China Sea

利用海相地层的沉积—地震响应关系结合地震波形—振幅响应技术可对砂、泥岩进行识别和精细解释,是低勘探程度地区海相地层岩性判别的重要手段。为此,选取北康盆地上渐新统—下中新统层序,以沉积—地震响应关系为基础,利用地震波形—振幅响应技术识别碎屑岩岩性组合。结果表明:(1)碎屑岩沉积过程与地震响应具有较好的耦合关系。(2)对于厚层砂、泥岩,地震反射界面较好地对应岩性界面,对于薄层砂、泥岩,地震波仅能大致确定砂、泥岩的厚度,地震反射界面与岩性界面不具有对应关系;砂、泥岩薄互层和岩性渐变的碎屑岩的地震响应特征容易产生多解性。(3)在厚度小于1/4波长的情况下,地质体顶、底面界面的反射波会产生干涉效应,该效应是波阻抗与岩层厚度共同作用的结果,因此应区别对待薄层砂、泥岩和厚层砂、泥岩以及砂泥岩薄互层的地震响应特征。(4)利用地震波形和振幅分析并结合视波阻抗差在剖面上建立的高精度地震剖面岩相展布,可以为烃源岩和储层预测提供可靠依据。文中方法可为南海海域等低勘探程度地区的岩性识别、烃源岩和储层预测提供可靠依据。

The identification and interpretation of sandstones and mudstones with the relationships between sedimentation and seismic response,and between seismic waveform and amplitude response is an important means of marine stratigraphic identification in under-explored areas.Combining these two relationships,we identify clastic rocks assemblage in the upper Miocene-lower Miocene sequences in the Beikang Basin.The following understandings are obtained:(1)There is a good coupling relationship between the sedimentary process of clastic rocks and seismic responses.(2)Seismic reflection interfaces correspond well to lithologic interfaces for thick sand and mudstone,but not for thin ones.Only thin bed thickness can be identified with seismic information,not its interfaces;Seismic response of thin inter-beds(sand,mudstone,clastic rocks)is prone to multiple solutions.(3)If geological body thickness is less than 1/4 wavelength,reflection waves of their tops and bottoms cause interference effects,these effects are the result of the interaction between wave impedance and strata thickness.Therefore,seismic response characteristics of sand,mudstone,and their inter-bed should be distinguished.(4)With seismic waveform and amplitude,and the difference of apparent impedance,high-precision lithofacies distributions can be established on seismic sections,which can provide reliable basis for hydrocarbon source rock and reservoir prediction.The proposed approach successfully applied in source rock and reservoir prediction in low exploration areas such as the South China Sea.