甜点地震属性理论诠释及应用

Theoretical annotation and application of sweetness

近年来,甜点和甜点属性常被地质和地球物理研究人员所提及。人们通常将沉积地层中局部油气有利区称为甜点,将反射强度与瞬时频率平方根的比值称为甜点属性。在对国内外原始文献进行系统调研基础上,制作了理论模型,定量说明了甜点属性的本质,给出了详细的理论诠释。研究表明:(1)瞬时振幅极性变换点对应希尔伯特变换的过零点,因为过零点两侧极性发生了改变,所以相位会有从180°到-180°的改变,此时瞬时频率会产生很大的野值;(2)在甜点属性修正式中N=2比N=1计算结果的压制异常效果好,至于N的取值,在理论上不好下定论,应根据具体资料特点进行测试、分析,对于文中实际资料N=2已满足要求;(3)在实际资料应用中,受储层厚度、埋深、资料信噪比和分辨率的影响,瞬时频率稳定性不好,不宜用剖面特征识别储层,而沿层甜点属性应用效果较好;(4)主频比瞬时频率更稳定,将反射强度与主频平方根的比值作为一种新的属性值——类甜点属性,在实际应用中可取得比常规甜点属性更好的结果;(5)对于有些瞬时振幅不具有高值、瞬时频率不具有低值的复杂储层,应先做映射,将它们映射成有利于井点属性评价的值,再计算甜点属性,这样会取得更好的结果。

In recent years,sweet spots or sweetness are often mentioned by geologists and geophysicists.They usually call local oil bearing beds in sedimentary strata as sweet spots,and the ratio of the reflection intensity to the square root of the instantaneous frequency is called sweetness.We consult systematically domestic and foreign references,and make a theoretical model to quantitatively illustrate sweetness,and give detailed theoretical interpretation.The following observations are obtained:A.The instantaneous amplitude polarity transformation point corresponds to the zero crossing of the Hilbert transform trace.Since the polarity of the two sides of the zero point has changed,the phase may change from 180°to-180°and the instantaneous frequency will produce large outliers;B.The suppressing abnormality effect of N =2 is much better than that of N=1 in the sweetness correction formula.The N=2 is not always good in theory,N should be tested and analyzed according to characteristics of actual data.N=2 has met the requirements for real data in the paper;C.In the real data application,with the influence of reservoir thickness and depth,signal-to-noise ratio(SNR),and resolution,the stability of instantaneous frequency may not be good.So it is better to identify sweetness along horizon than to identify reservoirs on section features on sections;D.The dominant frequency is more stable than the instantaneous frequency,so the ratio of the reflective intensity to the square root of the dominant frequency is a new attribute value,class sweetness,which can get better results than the sweetness in real data applications;E.For some complex reservoirs without high instantaneous amplitude and low instantaneous frequency,we should map them to favorable values and then calculate sweetness to obtain the better result.