流花地区巨厚灰岩层下伏构造落实方法研究

流花地区珠江组碳酸盐岩台地广泛发育巨厚的生物礁、滩灰岩。灰岩层和上、下碎屑岩地层之间存在巨大的速度差异,灰岩顶面地震能量屏蔽作用强,灰岩层内幕有效地震信号弱,加之灰岩层非均值性强,横向速度变化快,因而灰岩内幕地震成像效果差,常规方法无法获得灰岩层下伏地层的真实构造形态,这是流花地区灰岩层下砂岩层系油气勘探亟待解决的问题。为落实流花地区A区块灰岩层下伏构造,首先应用井震联合速度建模技术精细落实灰岩层顶面构造;然后基于压缩感知理论对反映灰岩层沉积相差异的地震低频信息进行补偿,并在层序地层格架控制下通过地震属性分析、沉积相研究,揭示多期次灰岩沉积相特征及速度特征;最后,采用相控约束地质统计学反演技术对灰岩层段进行波阻抗反演,基于反演结果构建灰岩层速度场并计算灰岩层厚度,进而落实灰岩层下伏构造形态,形成了一套巨厚灰岩层下伏构造落实方法。该方法可基本落实流花地区灰岩层下伏构造形态,对该地区灰岩层下砂岩地层的构造评价及勘探实践具有一定参考意义。

The carbonate platform of the Zhujiang formation in the Liuhua area is characterized by very thick reef and beach limestone strata.The shear wave velocity of limestone is significantly different from that of the underlying and overlying clastic rock strata.On the other hand,the heterogeneity of the formation and its strong shielding effect with respect to the seismic signal results in poor imaging of the inner features of the formation as well as of the strata underneath.In this work,a method was proposed to address these limitations and confirm the structural information of the clastic strata below the thick limestone formation.First,a joint velocity model based on well logging and seismic data was developed to accurately confirm the top structure of the limestone.Second,based on the theory of compressed sensing,the effect of the low-frequency seismic information,which reflects the differences of sedimentary facies in limestone,was compensated.Then,using a sequence-stratigraphic framework as an additional constraint,the characteristics of the sedimentary facies and the velocity distribution within the structures in the limestone formations were revealed by analyzing the seismic attributes and the information on the facies.Finally,the impedance inversion of the limestone section was carried out using the facies-controlled geostatistical inversion.Based on the results of the inversion,the velocity field within the limestone was constructed,the thickness of the formation was calculated,and the underlying structure was confirmed.The proposed technique provides a novel way to confirm the structure of the clastic strata underneath the very thick limestone formation in the Liuhua area.