地震波形指示反演在东营凹陷王家岗地区沙四上亚段滩坝砂的应用

以东营凹陷王家岗沙四上亚段滩坝砂为例,在层序地层格架建立的基础上,利用沉积学原理,基于贝叶斯理论将地震、测井和地质统计学信息融合为地层模型参数的后验概率分布,采用Metropolis-Hastings抽样算法对后验概率分布随机抽样,获得反演解,从而预测有利滩坝相带。结果表明:东营凹陷王家岗地区沙四上亚段低位域发育滩坝砂,其中准层序组2沉积时期以坝砂为主,砂体厚且横向分布稳定,而准层序组1和准层序组3沉积时期滩砂和坝砂间互发育,砂体厚度相对较小;湖侵域和高位域主要发育碳酸盐岩滩坝,滩坝砂零星状分布。该方法体现了相控的思想,预测结果更符合地质规律,在东营凹陷沙四上亚段滩坝储层预测中取得了较好的效果,为同类型储层预测提供了有利支持。

Application of seismic waveform inversion in Ess4 beach-bar sandstone in Wangjiagang area, Dongying Depression

The focus of the paper is the upper part of the fourth member of Shahejie Formation (Es^s₄) in Wangjiagang area, Dongying Depression. Based on Bayesian theory, a posterior probability density function of subsurface models was developed by establishing sequence stratigraphy framework, integrating the principles of sedimentology and information from seismic, well logs and geostatistics. The Metropolis-Hastings algorithm was applied to obtain an exhaustive characterization of the posterior probability density to predict the favorable beach-bar sedimentary facies. Results show that in the beach-bar sand development in the lowstand system tract (LST) of the Es^s₄, the bar sand is well developed, relatively thick, has large scale distribution, and less lateral variation in the second order para-sequence. The bar sand is interbedded with beach sand, and the overall thickness of the sand is relatively small in the first and third order para-sequences. The lacustrine transgressive system tracts (TST) and the highstand system tracts (HST) are mainly developed the carbonate beach-bar, and are less developed in sandy beach-bar. The aforementioned method is facies-controlled, which yields results that are more consistent with the geological observations. The proposed method works preferably in the Es^s₄, but may also be applied to other types of reservoirs.