Impedance inversion of pre-stack seismic data in the depth domain

The extensive application of pre-stack depth migration has produced huge volumes of seismic data,which allows for the possibility of developing seismic inversions of reservoir properties from seismic data in the depth domain.It is difficult to estimate seismic wavelets directly from seismic data due to the nonstationarity of the data in the depth domain.We conduct a velocity transformation of seismic data to make the seismic data stationary and then apply the ridge regression method to estimate a constant seismic wavelet.The estimated constant seismic wavelet is constructed as a set of space-variant seismic wavelets dominated by velocities at different spatial locations.Incorporating the weighted superposition principle,a synthetic seismogram is generated by directly employing the space-variant seismic wavelets in the depth domain.An inversion workflow based on the model-driven method is developed in the depth domain by incorporating the nonlinear conjugate gradient algorithm,which avoids additional data conversions between the time and depth domains.The impedance inversions of the synthetic and field seismic data in the depth domain show good results,which demonstrates that seismic inversion in the depth domain is feasible.The approach provides an alternative for forward numerical analyses and elastic property inversions of depth-domain seismic data.It is advantageous for further studies concerning the stability,accuracy,and efficiency of seismic inversions in the depth domain.

Fluid discrimination incorporating amplitude variation with angle inversion and squirt flow of the fluid

Pre-stack seismic inversion is an important method for fluid identification and reservoir characterization in exploration geophysics. In this study, an effective fluid factor is initially established based on Biot poroelastic theory, and a pre-stack seismic inversion method based on Bayesian framework is used to implement the fluid identification. Compared with conventional elastic parameters, fluid factors are more sensitive to oil and gas. However, the coupling effect between rock porosity and fluid content is not considered in conventional fluid factors, which may lead to fuzzy fluid identification results. In addition,existing fluid factors do not adequately consider the physical mechanisms of fluid content, such as squirt flow between cracks and pores. Therefore, we propose a squirt fluid factor(SFF) that minimizes the fluid and pore mixing effects and takes into account the squirt flow. On this basis, a novel P-wave reflection coefficient equation is derived, and the squirt fluid factor is estimated by amplitude variation with offset(AVO) inversion method. The new reflection coefficient equation has sufficient accuracy and can be utilized to estimate the parameters. The effectiveness and superiority of the proposed method in fluid identification are verified by the synthetic and field examples.

基于同步压缩匹配追踪的砂体尖灭点识别研究

砂体尖灭的刻画是构造岩性复合圈闭有效性评价的关键,而受地震资料带限影响难以准确识别砂体的尖灭位置。为了有效解决地震剖面上尖灭识别不准的问题,本文创新引入同步压缩匹配追踪时频分辨率和能量聚焦性双重优势开展砂体尖灭识别研究。首先利用时频域褶积算子与初始模型约束构建匹配追踪的冗余字典,在时频域内筛选出所有可能的匹配原子构成备选原子库;将初始模型约束与时频域联合反演方法引入反演框架,可获得更精确的反演结果;再利用同步压缩匹配追踪变换,通过逐道分析提取优势频率,筛选时频瞬时谱,得到具有最优频率的单频谱剖面。对所提方法进行的二维模型及实际资料的测试,结果表明,基于同步压缩匹配追踪的高分辨率地震谱分解砂体尖灭点识别方法能够获得更丰富的时频域信息,得到最优频率的单频谱剖面,进而精确识别地下地质体尖灭位置。该方法对超覆型及削蚀型岩性圈闭尖灭线的刻画具有重要的借鉴意义。

Seismic wave scattering inversion for fluid factor of heterogeneous media

Elastic wave inverse scattering theory plays an important role in parameters estimation of heterogeneous media.Combining inverse scattering theory,perturbation theory and stationary phase approximation,we derive the P-wave seismic scattering coefficient equation in terms of fluid factor,shear modulus and density of background homogeneous media and perturbation media.With this equation as forward solver,a pre-stack seismic Bayesian inversion method is proposed to estimate the fluid factor of heterogeneous media.In this method,Cauchy distribution is utilized to the ratios of fluid factors,shear moduli and densities of perturbation media and background homogeneous media,respectively.Gaussian distribution is utilized to the likelihood function.The introduction of constraints from initial smooth models enhances the stability of the estimation of model parameters.Model test and real data example demonstrate that the proposed method is able to estimate the fluid factor of heterogeneous media from pre-stack seismic data directly and reasonably.

多角度同步反演在南海西部气田开发中的应用

在海上开发的油气田中,由于钻井数量,地震资料的应用在气田的管理中具有非常重要的作用,特别是在气田开发的中后期,常规的烃类检测技术和波阻抗反演技术已经无法解决储层物性横行变化的问题和剩余气分布的问题。通过采用多角度联合弹性反演技术获得的弹性参数来描述储层的物性变化和剩余油气分布,基本达到半定量的水平,为气田的下一步开发调整奠定了基础。研究表明,多角度同步弹性反演(AVA反演)得到的泊松比、纵横波组速度比可以定性识别含气储层和含水储层,利用纵横波组速度比与纵波波阻抗进行交会的办法可以半定量解释出气层的饱和度,反演结果可以用于未知目标的预测。

基于贝叶斯理论的裂缝性介质叠前地震同步反演方法

裂缝的发育使储层表现出方位各向异性,而不同方位的叠前地震数据则表现出在振幅等属性上存在一定差异。所以,基于方位地震数据的叠前地震同步反演方法能获取储层裂缝相关参数,进而进行储层裂缝预测。为此,从方位各向异性介质的基本理论出发,介绍描述裂缝性介质的岩石物理参数,并给出各向异性参数与裂缝参数之间的转换关系。针对分步反演法可能产生累积误差的缺点,结合贝叶斯理论,提出裂缝性介质叠前地震同步反演方法。模型测试和实际资料测试结果均表明,新方法具有较好的可靠性和稳定性。

霸县凹陷南洼槽沉积相研究及岩性地层圈闭识别

通过对霸县凹陷南洼槽构造、沉积特征和成藏条件研究,首次建立了该区古近系层序地层等时格架,将沙一下亚段—沙四段划分为7套三级层序,明确了沉积体系及沉积相在等时地层格架内的空间展布及特征,指出文安斜坡内带、"凹中隆"背斜构造带和洼槽带为3个岩性地层圈闭发育的有利区带。综合应用地震相分析、地震属性分析及地震反演等技术进行岩性地层圈闭的有效识别。构建了斜坡带、背斜带和洼槽区岩性地层油藏模式,对有利勘探目标进行精细落实优选,钻探文安1、文安11井均获成功,研究表明该区是岩性地层油藏规模勘探的有利区,对冀中坳陷富油气凹陷岩性地层油藏勘探具有一定指导作用。

Near-surface absorption compensation technology and its application in the Daqing Oilfields

High-frequency seismic data components can be seriously attenuated during seismic wave propagation in unconsolidated （low-velocity） layers, resulting in reduced seismic resolution and signal-to-noise （S/N） ratio. In this paper, first, based on Wiener filter theory, inverse filter calculations for near-surface absorption attenuation compensation were accomplished by analysis of the direct wave spectral components from different distances near the surface. The direct waves were generated by detonators in uphole shots and were acquired by receivers on the surface. The spatially varying inverse filters were designed to compensate for the frequency attenuation of 3D pre-stack CRG （common receiver-gather） data. After applying the filter to CRG data, the high frequency components were compensated with the low frequencies maintained. The seismic resolution and S/N ratio are enhanced and match better with synthetic seismograms and better meet the needs of geological interpretation.

Sweet spot prediction in tight sandstone reservoir based on well-bore rock physical simulation

To establish the relationship among reservoir characteristics and rock physical parameters,we construct the well-bore rock physical models firstly,considering the influence factors,such as mineral composition,shale content,porosity,fluid type and saturation.Then with analyzing the change rules of elastic parameters along with the above influence factors and the cross-plots among elastic parameters,the sensitive elastic parameters of tight sandstone reservoir are determined,and the rock physics template of sweet spot is constructed to guide pre-stack seismic inversion.The results show that velocity ratio and Poisson impedance are the most sensitive elastic parameters to indicate the lithologic and gas-bearing properties of sweet spot in tight sandstone reservoir.The high-quality sweet spot is characterized by the lower velocity ratio and Poisson impedance.Finally,the actual seismic data are selected to predict the sweet spots in tight sandstone gas reservoirs,so as to verify the validity of the rock physical simulation results.The significant consistency between the relative logging curves and inversion results in different wells implies that the utilization of well-bore rock physical simulation can guide the prediction of sweet spot in tight sandstone gas reservoirs.

利用叠前密度反演预测岩性的应用研究

珠江口盆地番禺某地区使用常规的叠后波阻抗较难识别储层岩性。使用叠前密度反演方法,即利用不同炮检距道集数据以及纵波、横波、密度等测井资料进行反演,同时反演出纵波阻抗、横波阻抗、密度等。利用该技术对该地区进行储层预测,结果表明密度可以有效的区分该区的储层,并能清楚反映出尖灭等地质现象;目的层SB21.0沿层属性展示出有利储层的分布区域,预测区得到了钻井证实,证明该技术是有效的。

Determination of gas reservoir(s) using AVO inversion within “XY” field offshore Niger Delta

The AVO inversion analysis of pre-stack seismic data of“XY”field located within the offshore,Niger Delta Basin has been considered in this research work with the aim of using AVO inversion to delineate gas reservoirs within the field.Three different inversion techniques are carried out in order to obtain accurate reservoir signature.The conventional AVO inversion analysis of the field do not identify the gas reservoirs clearly as there are other zones without gas with similar signatures,however,the cross-plots analysis of elastic parameters and the inverted volumes are used to delineate two gas reservoirs at 2000 and 2100 ms.Conclusively,the inversion techniques help to map the reservoir zone in a better way by increasing the vertical resolution.AVO inversion analysis as used in this research help for better understanding of the physical properties of the delineated reservoirs.