地震可检测性分辨率研究

Research on seismic detectable resolution

探测厚度小于或远小于λ/4的薄层(薄煤层、薄砂岩储层等)以及宽度有限或长度、宽度有限且高度小于λ/4的非规则二度体(如地下暗河)和三度体(如溶洞)已是地震勘探的重要目标。近年来,这方面的探索研究已经取得一定进展。但人们对厚度(高度)小于λ/4的薄层(非规则体)能否被检测出来产生了质疑。分析表明,常用的分辨率定义(如瑞利、瑞克的λ/4、威迪斯的λ/8等)是用地震波的特征确定薄层厚度的,可以用其回答"薄层有多薄"的问题,因此,准确地说,上述分辨率应该称之为薄层厚度分辨率。用这类分辨率定义来判断薄层是否可被检测,有其不适应性。研究表明,薄层(非规则体)能否被检测的关键是其反射波(属性)能否从背景反射(属性)中区分出来,用这一思想可以回答"多薄的薄层、多小的非规则体可以被检测"的问题,这即是地震可检测性分辨率。讨论了薄层和非规则体可检测性分辨率的一些定量指标,给出了薄煤层、碳酸盐岩溶洞型储集体和薄砂岩储层检测的实例。

The detection of layers which thickness(height) is less or far less than λ/4(such as thin coal bed and thin sand reservoir) have become an important target for seismic exploration,so do the irregular 2-D(such as undercurrent) and 3-D bodies(such as caves) thinner than λ/4 with limited width or with limited width & length.In recent years,researchers have made some progress on the above targets.However,it is doubted that the layer with thickness(height) smaller than λ/4 can be detected.The definition of the conventional seismic resolution such as λ/4(Rayleigh or Ricker) or λ/8(Widess) is by using the characteristics of seismic wave to verify the thickness of thin layers,which can be used to answer 'how thin for a thin layer'.Therefore,the above resolutions should be called as 'Resolution on thickness of thin layer'.This kind of resolution is not adaptive to estimate whether the bed is detectable.Research indicates that the essence of thin layer can be detected is that its reflection(attributes) could be distinguished from its background(attributes).In terms of this theory,one new resolution is presented,which is called as seismic detectable resolution.The seismic detectable resolution answers the questions of 'what is the minimum thickness of detectable thin bed' and 'what is the minimum size of detectable irregular body'.In the paper,we discussed some quantitative indexes for the detectable resolution of thin layers and irregular bodies,and displayed some detection samples for thin coal bed,carbonate carven reservoirs and thin sand reservoirs.