波形指示叠前地震反演方法在致密含油薄砂层预测中的应用

摘要

岩石物理研究的实践表明,叠前弹性参数及其多参数交会对储层和烃类更为敏感,以此为基础的叠前地震反演是定量预测含油气储层的有效方法.对于致密砂岩薄储层及其含油性预测而言,因其地震响应极其隐蔽、地震信号分辨率不足,目前普遍采用基于变差函数理论的高分辨率叠前随机反演方法,但其反演结果的高频成分随机性较强、可靠性降低,对预测结果的精度和可靠性造成较大的影响.为解决上述问题,以四川盆地中北部地区侏罗系沙溪庙组致密含油薄砂层的预测为例,在储层及含油性敏感弹性参数分析的基础上,开展了波形指示叠前地震高分辨率反演方法的应用研究.该方法利用叠前地震波形相似性代替传统变差函数优选测井样本,并以此进行随机模拟建立各弹性参数的初始模型;在贝叶斯框架下,联合初始模型、测井弹性参数先验概率分布和叠前同时反演弹性参数结果建立后验概率分布,对其进行Metropolis-Hastings采样得到收敛的平稳分布即为一个反演实现.实际应用效果表明,波形指示叠前地震反演方法能够从叠前地震资料中获取地层各项弹性参数的高分辨率宽频结果,且其高频成分的确定性增强,提高了致密砂岩薄储层及含油性的预测精度和可靠性.该项技术是陆相致密碎屑岩储层及含油气性高精度预测的有效方法,具有广阔的应用前景.%The results of petro-physical research show that pre-stack elastic parameters and multi-parameter intersection are more sensi-tive to reservoir and hydrocarbon,and the pre-stack inversion based on this conclusion is an effective method for quantitative prediction of the oil-bearing reservoir.As for compact and thin sand reservoir and its oil-bearing property,because their seismic response are ex-tremely concealed and the seismic resolution is deficient,the high-resolution pre-stack stochastic inversion based on variogram is widely applied.However,the high frequency contents of pre-stack stochastic inversion have strong randomness and low reliability,which exerts a great impact on the accuracy and reliability of the prediction results.In order to solve these problems,the authors took the prediction for compact and oil-bearing thin sand of Jurassic Shaximiao Formation in north-central Sichuan Basin as a study case and,after analyzing the sensitive elastic parameters of reservoir and its oil-bearing property,carried out the application research on the high-resolution pre-stack inversion method based on seismic waveform indicator.The method uses the similarity of pre-stack seismic waveform instead of var-iogram to optimize well samples,and builds the initial model of each elastic parameter by stochastic simulating based on the optimization samples.Under a Bayesian framework,the method combines the initial model,the prior probability distribution of well elastic parameters and the inversion elastic parameters of pre-stack simultaneous inversion to build the posterior probability distribution of each elastic pa-rameter,then resamples the posterior probability distribution function using Metropolis-Hastings method to get a convergent and stationa-ry distribution which is also an inversion result.The practical application shows that it can get a high-resolution and broadband result of each elastic parameter in the formation from the pre-stack seismic data by using the pre-stack inversion based on seismic waveform indi-cator,and the high frequency contents of the result are more certain to raise the prediction accuracy and reliability of compact and thin sand reservoir and its oil-bearing property.It has extensive application prospect as an effective method for high-precision prediction of the reservoir and the oil-bearing property of compact clastic rocks in terrestrial facies.