Ensemble-based conditioning of reservoir models to seismic data

While 3D seismic has been the basis for geological model building for a long time, time-lapse seismic has primarily been used in a qualitative manner to assist in monitoring reservoir behavior. With the growing acceptance of assisted history matching methods has come an equally rising interest in incorporating 3D or time-lapse seismic data into the history matching process in a more quantitative manner. The common approach in recent studies has been to invert the seismic data to elastic or to dynamic reservoir properties, typically acoustic impedance or saturation changes. Here we consider the use of both 3D and time-lapse seismic amplitude data based on a forward modeling approach that does not require any inversion in the traditional sense. Advantages of such an approach may be better estimation and treatment of model and measurement errors, the combination of two inversion steps into one by removing the explicit inversion to state space variables, and more consistent dependence on the validity of assumptions underlying the inversion process. In this paper, we introduce this approach with the use of an assisted history matching method in mind. Two ensemble-based methods, the ensemble Kalman filter and the ensemble randomized maximum likelihood method, are used to investigate issues arising from the use of seismic amplitude data, and possible solutions are presented. Experiments with a 3D synthetic reservoir model show that additional information on the distribution of reservoir fluids, and on rock properties such as porosity and permeability, can be extracted from the seismic data. The role for localization and iterative methods are discussed in detail.     

陆相薄互层稠油油藏热采时移地震监测互均衡处理效果分析

陆相储层稠油热采时移地震监测数据开展的互均衡处理结果表明,此项处理有利于有效时移地震异常的识别与热前缘位置的准确确定。当原始采集资料的一致性极差时,互均衡处理虽然可以改善资料的一致性,因此,提高野外采集震源子波和采集资料的一致性,是陆相薄互层油藏时移地震监测顺利实施的关键。振幅属性是陆相薄储层油藏时移地震监测的主要标志之一,笔者在振幅处理方面做了一些探索,取得一定效果。     

Impact of time-lapse seismic data for permeability estimation

We consider the impact of using time-lapse seismic data in addition to production data for permeability estimation in a porous medium with multiphase fluid flows, such as a petroleum reservoir under water-assisted production. Since modeling seismic wave propagation in addition to modeling fluid flows in the reservoir is quite involved, it is assumed that the time-lapse seismic data have already been inverted into fluid saturation differences (pseudoseismic data). Because an inversion process often leads to considerable error growth, we will consider pseudoseismic data with large uncertainties. The impact of pseudoseismic data is assessed through permeability estimation with and without such data and through application of some uncertainty measures for the estimated parameters. A multiscale algorithm is used for the parameter estimations, so that potential differences in attainable permeability resolution will be easily revealed. The numerical examples clearly indicate that the permeability estimation problem is stabilized at a higher level of resolution when pseudoseismic data are applied in addition to production data, even if the pseudoseismic data have large associated uncertainties. Use of the parameter uncertainty measures confirm these results.     

Using time-lapse 4D seismic to monitor saturation changes in carbonate reservoirs

In the past ten years, time-lapse (4D) seismic has evolved as a standard way of monitoring reservoir performance. The method is now being used as good reservoir management practice to provide evidence of saturation changes within the reservoir at field scale. 4D provides a new piece of data describing the dynamic behavior of the reservoir fluids between the wells, often limited to small scale monitoring at the borehole scale. Thus, it provides sophisticated techniques for reservoir monitoring and management relying on the integration of geological models, static and dynamic properties of the reservoir rock, and detailed production and pressure field data.While 4D seismic data has been very successful in monitoring hydrocarbon production from clastic reservoirs, this work has focused on implementing 4D time lapse to monitor saturation changes in carbonate reservoirs and it’s capability to be used as enhanced oil recovery (EOR) tool that can help in enhancing the recovery factor for the filed and help to locate new drilling to sweep more oil out of the reservoir and locate the by-pass oil.The principal goal of this research was to detect the maximum change in seismic attributes (amplitude, acoustic impedance, travel time) that could occur as a result of oil production, water and gas injection in carbonate reservoirs by using time-lapse 4D seismic.     

Local adaptive parameterization for the history matching of 3D seismic data

Matching seismic data in assisted history matching processes can be a challenging task. One main idea is to bring flexibility in the choice of the parameters to be perturbed, focusing on the information provided by seismic data. Local parameterization techniques such as pilot-point or gradual deformation methods can be introduced, considering their high adaptability. However, the choice of the spatial supports associated to the perturbed parameters is crucial to successfully reduce the seismic mismatch. The information related to seismic data is sometimes considered to initialize such local methods. Recent attempts to define the regions adaptively have been proposed, focusing on the mismatch between simulated and reference seismic data. However, the regions are defined manually for each optimization process. Therefore, we propose to drive the definition of the parameter support by performing an automatic definition of the regions to be perturbed from the residual maps related to the 3D seismic data. Two methods are developed in this paper. The first one consists in clustering the residual map with classification algorithms. The second method proposes to drive the generation of pilot point locations in an adaptive way. Residual maps, after proper normalization, are considered as probability density functions of the pilot point locations. Both procedures lead to a complete adaptive and highly flexible perturbation technique for 3D seismic matching. A synthetic study based on the PUNQ test case is introduced to illustrate the potential of these adaptive strategies.     

History matching time-lapse seismic data using the ensemble Kalman filter with multiple data assimilations

The ensemble Kalman filter (EnKF) has become a popular method for history matching production and seismic data in petroleum reservoir models. However, it is known that EnKF may fail to give acceptable data matches especially for highly nonlinear problems. In this paper, we introduce a procedure to improve EnKF data matches based on assimilating the same data multiple times with the covariance matrix of the measurement errors multiplied by the number of data assimilations. We prove the equivalence between single and multiple data assimilations for the linear-Gaussian case and present computational evidence that multiple data assimilations can improve EnKF estimates for the nonlinear case. The proposed procedure was tested by assimilating time-lapse seismic data in two synthetic reservoir problems, and the results show significant improvements compared to the standard EnKF. In addition, we review the inversion schemes used in the EnKF analysis and present a rescaling procedure to avoid loss of information during the truncation of small singular values.     

时移地震数据空间偏差校正方法

时移地震油藏监测技术是直接确定剩余油分布的关键技术之一。针对时移地震油藏监测在国内的需求及推广应用难点,研究了时移地震数据空间偏差校正处理方法。由于在观测系统、采集方向的处理参数等方面的差异,导致地下同一反射点在不同时移地震数据偏移后空间位置存在差异,产生与油藏变化无关的地震差异,增加数据解释的难度和风险。通过对参考数据与监测数据三维空间内的局部数据体的三维相关计算,确定监测数据体在x方向、y方向和时间方向上最佳移动量,从而实现两次地震数据空间位置差异校正。实际时移地震数据处理试验结果分析表明,空间偏差校正处理方法在消除时移地震数据三维空间非线性空间偏差方面是有效的。     

Approximate Derivative Computations for the Gradient-Based Optimization Methods in the Local Gradual Deformation for History Matching

Reservoir characterization needs the integration of various data through history matching, especially dynamic information such as production or four-dimensional seismic data. To update geostatistical realizations, the local gradual deformation method can be used. However, history matching is a complex inverse problem, and the computational effort in terms of the number of reservoir simulations required in the optimization procedure increases with the number of matching parameters. History matching large fields with a large number of parameters has been an ongoing challenge in reservoir simulation. This paper presents a new technique to improve history matching with the local gradual deformation method using the gradient-based optimizations. The new approach is based on the approximate derivative calculations using the partial separability of the objective function. The objective function is first split into local components, and only the most influential parameters in each component are used for the derivative computation. A perturbation design is then proposed to simultaneously compute all the derivatives with only a few simulations. This new technique makes history matching using the local gradual deformation method with large numbers of parameters tractable.     

基于匹配追踪时—频分解技术的辫状河道油藏储层预测简

The braided channel sedimentary sand is a kind of common oil reservoir, which is characteristic of poor regularity structure and complicated oil water relation. Seismic trace can be remodeled by wavelet decomposition, namely seismic trace is decomposed into a series of different attribute wavelets. The different reflection is obtained by the different attribute wavelets, thus prediction accuracy of braided channel sedimentary sand is improved. The seismic signal treated by matching pursuit method has good focusing capability of instantaneous spectrum, based on which the seismic signal is simply and rapidly remodeled by time frequency decomposition. The seismic data of Kendong 701 area were processed based on matching pursuit time frequency decomposition. The results showed that the interpretability of oil reservoir was improved and the seismic reflection characteristics and drilling data were well related. The braided channel sedimentary sands of Minghuazheng and Guantao group strata in Kendong 701 area were predicted, and the results showed that the reservoir distribution had the obvious braided channel features. Based on the predictions, three wells were located and the prediction and drilled results were consistent.     

Gradient-based Pareto optimal history matching for noisy data of multiple types

The advantages of the simultaneous integration of production and time-lapse seismic data for history matching have been demonstrated in a number of previous studies. Production data provide accurate observations at particular spatial locations (wells), while seismic data enable global, though filtered/noisy, estimates of state variables. In this work, we present an efficient computational tool for bi-objective history matching, in which data misfits for both production and seismic measurements are minimized using an adjoint-gradient approach. This enables us to obtain a set of Pareto optimal solutions defining the optimal trade-off between production and seismic data misfits (which are, to some extent, conflicting). The impact of noise structure and noise level on Pareto optimal solutions is investigated in detail. We discuss the existence of the “best” trade-off solution, or least-conflicting posterior model, which corresponds to the history-matched model that is expected to provide the least-conflicting forecast of future reservoir performance. The overall framework is successfully applied in 2D and 3D compositional simulation problems to provide a single least-conflicting posterior model and, for the 2D case, multiple samples from the posterior distribution using the randomized maximum likelihood method.     

Assimilating spatially dense data for subsurface applications—balancing information and degrees of freedom

The degrees of freedom (DOF) in standard ensemble-based data assimilation is limited by the ensemble size. Successful assimilation of a data set with large information content (IC) therefore requires that the DOF is sufficiently large. A too small number of DOF with respect to the IC may result in ensemble collapse, or at least in unwarranted uncertainty reduction in the estimation results. In this situation, one has two options to restore a proper balance between the DOF and the IC: to increase the DOF or to decrease the IC. Spatially dense data sets typically have a large IC. Within subsurface applications, inverted time-lapse seismic data used for reservoir history matching is an example of a spatially dense data set. Such data are considered to have great potential due to their large IC, but they also contain errors that are challenging to characterize properly. The computational cost of running the forward simulations for reservoir history matching with any kind of data is large for field cases, such that a moderately large ensemble size is standard. Realization of the potential in seismic data for ensemble-based reservoir history matching is therefore not straightforward, not only because of the unknown character of the associated data errors, but also due to the imbalance between a large IC and a too small number of DOF. Distance-based localization is often applied to increase the DOF but is example specific and involves cumbersome implementation work. We consider methods to obtain a proper balance between the IC and the DOF when assimilating inverted seismic data for reservoir history matching. To decrease the IC, we consider three ways to reduce the influence of the data space; subspace pseudo inversion, data coarsening, and a novel way of performing front extraction. To increase the DOF, we consider coarse-scale simulation, which allows for an increase in the DOF by increasing the ensemble size without increasing the total computational cost. We also consider a combination of decreasing the IC and increasing the DOF by proposing a novel method consisting of a combination of data coarsening and coarse-scale simulation. The methods were compared on one small and one moderately large example with seismic bulk-velocity fields at four assimilation times as data. The size of the examples allows for calculation of a reference solution obtained with standard ensemble-based data assimilation methodology and an unrealistically large ensemble size. With the reference solution as the yardstick with which the quality of other methods are measured, we find that the novel method combining data coarsening and coarse-scale simulations gave the best results. With very restricted computational resources available, this was the only method that gave satisfactory results.     

流体替代的地震反射振幅特征分析

在油田的开发阶段,注水或注气开采会引起储层物性的变化,同时储层所含流体也会发生改变,这就为时移地震监测提供了可能.笔者主要基于Gassmann方程,详细地论述了孔隙流体替代储层地震波速度和密度变化规律,并且根据预测的结果建立了含水饱和度变化地震地质模型.最后通过对该模型的振幅类地震属性分析,对地震属性进行了优选,找到了适合本工区时移地震监测的敏感性振幅属性,为预测工区剩余油的分布提供了基础.     

海上时移地震数据处理关键技术

分析了时移地震地球物理机制及造成时移地震数据差异的非地质因素,论述了海上拖缆采集的时移地震数据处理的关键技术。实例证明,这些技术可以改善时移地震资料处理结果的一致性,提高差异剖面的可靠性,为油气藏开发过程的监测提供准确信息。     

Stratimagic波形地震相分析在层序地层岩性分析中的应用

应用波阻抗反演以及常规地震属性预测储层时,在钻井资料较少、储层较薄的情况下多解性较强。Stratimagic波形地震相分析技术采用神经网络算法对某一层间的地震数据道进行逐道对比分类,细致刻画地震信号的横向变化,从而得到与地质相对应的地震相图,并以此用于储层砂体和地层岩性油藏的预测。以东营凹陷八面河地区滩坝砂体岩性油藏为例,说明应用该方法进行滩坝砂体和岩性油藏分布预测,是行之有效的。      

A Critical Comparison of Three Methods for Time-Lapse Time-Shift Calculation

Time-shift, one of the most popular time-lapse seismic attributes, has been widely used in dynamic reservoir characterization by linking it with pressure and geomechanical changes. Therefore, it is important to select appropriate calculation methods according to different time-lapse seismic data quality and time-shift magnitude. To date, there have been various published works comparing different time-shift calculation methods and discussing their advantages and disadvantages. However, most of these comparisons are based only on synthetic tests or single field applications. As the quality of time-lapse seismic data and time-shift magnitude can vary in different fields, one method may not work consistently well for each case. In this paper, a critical comparison of three different time-shift calculation techniques (Hale’s fast cross-correlation, Rickett’s non-linear inversion, and Whitcombe’s correlated leakage method) is provided. The three methods are applied to a set of synthetic data sets that are designed to account for various seismic noise and time-shift magnitudes. They are also applied to four real time-lapse seismic data sets from three North Sea fields. The calculated time-shift results are compared with the input (in synthetic tests) or the real observations from information such as seabed subsidence and compaction (in field applications). Both qualitative and quantitative comparisons are performed. At the end, each of the time-shift methods is evaluated based on different aspects, and the most appropriate method is suggested for each data scenario. All three time-shift methods are found to successfully measure time-shifts. However, Rickett’s non-linear inversion is the most outstanding method, as it gives smooth time-shifts with relatively good accuracy, and the derived time strains are more stable and interpretable.

     

时移地震数据重复性度量及一致性分析方法

时移地震的可重复性高低是时移地震成功与否的关键,因此需要有效的时移地震数据重复性度量及一致性分析方法。这里首先分析了常用的时移地震数据重复性度量方法,即NRMS和PRED方法。经研究发现,PRED度量方法对地震数据的差异性并不敏感,因此提出了基于第三代相干分析的COHE度量方法,COHE方法比PRED方法对地震数据的差异性更为敏感。NRMS和COHE方法可以度量地震数据的重复性,但不能直接分析不一致性的影响因素,因此这里引入地震数据处理中的相关参数分析法,提出了基于相关函数的时移地震数据一致性分析方法,求取相关函数的特征参数,可以直观地分析时移地震数据在时间、振幅、相位和频率等方面的一致性,指导时移地震数据的处理,进行质量监控。     

时延爆炸理论及应用研究

地震波激发方式是影响地震数据采集质量的主要因素之一。本文以野外试验数据为基础，对时延爆炸法原理进行了分析。运用数值模拟和其它数学手段，分析了延迟爆炸情况下地震波主频、频宽、能量的变化规律，研究了入射角对上述因素的影响特征。分析表明：相同药量条件下，采用延迟爆炸的激发方式可增大地震波主频，拓宽地震波的频带宽度，增大向下传播的地震波能量；在常规地震勘探的入射角范围内进行时延爆炸激发时，由入射角变化所引起的地震波波形及其频谱的畸变可忽略不计。     

基于水合物指示因子的地震识别方法

速度是水合物勘查的重要参数,但是速度的影响因素众多,给高精度识别水合物带来一定困难.水合物储层岩石物理是研究多种因素对速度影响的有效手段之一.考虑到水合物储层未固结等特征,本文采用SCA-DEM模型,重点对比了孔隙度、饱和度等对纵横波速度以及AVO特征的影响,并构建了一种新的水合物指示因子,消除了由于孔隙变化带来的假异...     

非平稳地震信号匹配追踪时频分析

根据三步法匹配追踪原理实现了基于雷克子波的地震信号自适应分解,在此基础上,讨论了利用匹配子波进行地震信号时频表征的方法。由于常规匹配追踪时频是以Wigner-Ville分布为基础,得到的时频信息有限,因此给出了一种基于可调窗口的短时傅氏变换时频表示方法,进而又利用各匹配子波的复谱,引入一种新的时频表示方法,不仅与Wigner-Ville方法具有同等的分辨率和能量聚集特性,而且保留了原信号的最基本时频特征,不存在交叉项和窗口截断效应。通过与短时傅氏变换和S变换时频特征的对比发现,匹配追踪时频表征和瞬时谱参数具有更高的分辨率。实际数据的应用也表明,匹配追踪分解非常适用于非平稳特征的地震信号的时频分析。