利用高密度地震技术精细刻画叠置火山岩

安达地区位于徐家围子断陷，营三段火山岩存在2个大的喷发期次（yc32、yc33），每个喷发期次由多个次级喷发期次构成。由于火山岩埋深大、隐蔽性高、物源特殊、形成机制多变、岩相变化快，导致火山体内部结构复杂。安达地区常规地震资料的地震成像垂向分辨率和振幅保真度低，难以准确识别和刻画各喷发期次的地层展布。为此，在高密度地震数据基础上，采用近地表补偿和黏弹性介质稳相叠前时间偏移，大幅提高了成像结果的垂向分辨率和振幅保真度；应用相干分析、层拉平及波形精细对比等地震解释技术，精细描述了叠置火山岩；通过井震结合，精细划分了火山岩喷发期次，将yc32细分为3期（yc32-1、yc32-2、yc32-3），yc33细分为2期（yc33-1、yc33-2）。最终获得以下成果：①yc33发育酸性岩，主要为火山角砾岩；yc32发育中基性火山岩，上部以安山岩为主，下部以玄武岩为主。②识别了2个玄武岩体（面积分别为2和22km²）、3个安山岩体（面积分别为1.6、6.5、22.6km²）。上述成果为火山岩气藏储层预测奠定了基础。

Depiction of superimposed volcanic edifices in detail by high-density seismic techniques

The Anda area is located in the Xujiaweizi fault depression, and there are two large erupting periods (yc32 and yc33) in volcanic edifices in the third member of Yingcheng Formation, each consisting of multiple secondary erupting periods. Because volcanic edifices are characterized by a large burial depth, high concealment, special provenance, variable formation mechanisms, and fast lithofacies change, their internal structures are complex. The conventional seismic data in the Anda area have low vertical resolution and amplitude fidelity, and thus the stratigraphic distribution in each erupting period is hard to be accurately identified and depicted. Therefore, based on high-density seismic data, near-surface compensation and pre-stack time migration with stationary phases in the viscoelastic medium are used to greatly improve the vertical resolution and amplitude fidelity of the imaging results. Seismic interpretation techniques such as coherence analysis, layer flattening, and fine waveform comparison are applied to finely describing superimposed volcanic edifices. Well logging and seismic data are combined to accurately divide the erupting periods of volcanic edifices. To be specific, yc32 is divided into three periods (yc32-1, yc32-2, and yc32-3) and yc33 into two periods (yc33-1 and yc33-2). Finally, the following results are obtained:① Acidic rocks, dominated by volcanic breccia, are mainly developed in yc33;in yc32, intermediate-basic volcanic edifices are mainly developed, dominated by andesite in the upper part and basalt in the lower part. ② Two basalt masses (with a respective area of 2 and 22km²) and three andesite masses (with a respective area of 1. 6, 6. 5, and 22. 6km²) are identified. The above achievements lay a foundation for predicting the gas reservoirs of volcanic edifices.