时移地震属性表征油藏参数动态变化机理研究是有效区分不同油藏参数变化,进行时移地震解释的理论基础,是时移地震实际应用的关键环节.从疏松砂岩油藏岩石物理研究出发,计算得到含油饱和度和有效压力变化引起纵、横波速度变化的明显差异.并以此为基础,通过解耦后的地震波动方程模型模拟,分析证明不同偏移距地震振幅对含油饱和度变化响应规律存在差异,分析得到油藏有效压力和含油饱和度变化时P-P反射波和P-S转换波叠前地震属性差异特征,对比分析了油藏有效压力和含油饱和度变化时的P-P反射波和P-S转换波AVO(Amplitude Versus Of fset,振幅随偏移距变化)属性变化规律和差异特征.理论模型研究结果证明了利用叠前时移地震信息(叠前地震属性和地震AVO信息)区分不同油藏参数动态变化的可行性和在有效提高时移地震资料解释精度方面的潜力.同时,研究也表明针对目标油田深入理解油藏参数变化的时移地震响应机理对制定有效的时移地震资料处理和解释方案十分重要.
We propose a novel method for seismic noise attenuation by applying nonstationary polynomial fitting （NPF）, which can estimate coherent components with amplitude variation along the event. The NPF with time-varying coefficients can adaptively estimate the coherent components. The smoothness of the polynomial coefficients is controlled by shaping regularization. The signal is coherent along the offset axis in a common midpoint （CMP） gather after normal moveout （NMO）. We use NPF to estimate the effective signal and thereby to attenuate the random noise. For radial events-like noise such as ground roll, we first employ a radial trace （RT） transform to transform the data to the time-velocity domain. Then the NPF is used to estimate coherent noise in the RT domain. Finally, the coherent noise is adaptively subtracted from the noisy dataset. The proposed method can effectively estimate coherent noise with amplitude variations along the event and there is no need to propose that noise amplitude is constant. Results of synthetic and field data examples show that, compared with conventional methods such as stationary polynomial fitting and low cut filters, the proposed method can effectively suppress seismic noise and preserve the signals.
Liu Guo-ChangChen Xiao-HongLi Jing-YeDu JingSong Jia-Wen
The filter operator used in normal multichannel matching filter is physically realizable. This filter operator only delays seismic data in the filtering process. A non- causal multichannel matching filter based on a least squares criterion is proposed to resolve the problem in which predicted multiple model data is later than real data. The differences between causal and non-causal multichannel matching filters are compared using a synthetic shot gather, which demonstrates the validity of the non-causal matching filter. In addition, a variable length sliding window which changes with offset and layer velocity is proposed to solve the count of events increasing with increasing offset in a fixed length sliding window. This variable length sliding window is also introduced into the modified and expanded multichannel matching filter. This method is applied to the Pluto1.5 synthetic data set. The benefits of the non-causal filter operator and variable length sliding window are demonstrated by the good multiple attenuation result.
Liu Hua-FengChen Xiao-HongSong Jia-WenLiu Guo-Chang
