Title
Dolomite reservoir prediction with lithology factor in the Maokou Formation, Fuling area, Sichuan Basin
摘要
川东南涪陵地区茅口组碳酸盐岩与上覆吴家坪组底部炭质泥岩存在较大波阻抗差，形成连续强反射界面T，屏蔽了下伏白云岩储层的地震响应，茅口组白云岩与灰岩纵波阻抗叠置，叠后地震难识别，原始CRP道集有效角度仅到20°，缺乏大角度信息，不利于叠前弹性参数求取。针对以上问题，在叠前道集优化处理基础上，采用多子波分解与重构技术对近、中角度的叠加数据进行了去强轴处理，再通过贝叶斯稀疏脉冲反演求取了两个叠加数据体的射线弹性阻抗体，最后利用近、中角度的射线弹性阻抗体通过坐标旋转技术构建了岩性因子，进行白云岩储层的有效识别。多子波分解与重构技术可有效压制炭质泥岩的强轴屏蔽，突显下伏白云岩储层的地震响应，提高储层预测精度，射线弹性阻体构建岩性因子规避了叠前道集大角度信息缺失、弹性参数难求取的问题。研究表明，涪陵地区茅口组三段白云岩储层主要呈团块状沿基底断裂分布，地震岩性因子预测的白云岩厚度与实钻井较吻合，该技术可有效解决白云岩储层难预测的问题，具一定的推广运用价值。
Abstract
Large P-wave impedance difference exists between the Maokou Fm.carbonates and overlying carbonaceous mudstones at the bottom of the Wujiaping Formation in Fuling area, southeastern Sichuan Basin, resulting in a continuous strong reflection interface(T), which shields the seismic response of the underlying dolomite reservoirs.Due to the superimposition of the P-wave impedance between dolomite and limestone in the Maokou Formation, post-stack seismic prediction of the dolomite reservoir is difficult.In addition, the effective angle of the original CRP gather is only 20°, and the lacking of high-angle information is unfavorable for the calculation of pre-stack elastic parameters.On the basis of the CRP gather optimization, superimposed near-and medium-angle data were formed with the technology of multi-wavelet decomposition and reconstruction.Then, the ray elastic impedance of the two superimposed data volumes was obtained by Bayesian sparse pulse inversion.The lithology factor was built by coordination rotation to identify dolomite reservoirs via the ray elastic impedances of near-and medium-angle information.Multi-wavelet decomposition and reconstruction can effectively suppress the strong inference of the carbonaceous mudstone, and highlight the seismic responses of dolomites, thus improving the accuracy of reservoir prediction.The lithology factor obtained can be applied to avoid problems relating to the lack of high-angle CRP gather and the difficulty in elastic parameter calculation.In conclusion, the dolomite reservoirs in the Mao 3 member are distributed in blocks along basement-rooted faults, the thickness out of seismic prediction by lithology factor is in good agreement with actual drilling data, indicating that the technology could be applied to the effective prediction of dolomite reservoirs, and is of promotional value in practice.
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