Efficient volumetric extraction of most positive/negative curvature and flexure for fracture characterization from 3D seismic data

Most positive/negative curvature and flexure are among the most useful seismic attributes for detecting faults and fractures in the subsurface based on the geometry of seismic reflections. When applied to fracture characterization and modelling of a fractured reservoir, their magnitude and azimuth help quantify both the intensity and orientation of fracturing, respectively. However, previous efforts focus on estimating only the magnitude of both attributes, whereas their associated azimuth is ignored in three‐dimensional (3D) seismic interpretation. This study presents an efficient algorithm for simultaneously evaluating both the magnitude and azimuth of most positive/negative curvature and flexure from 3D seismic data. The approach implemented in this study is analytically more accurate and computationally more efficient compared with the existing approach. The added value of extracting most positive/negative curvature and flexure is demonstrated through the application to a fractured reservoir at Teapot Dome (Wyoming). First, the newly extracted attributes make computer‐aided fault/fracture decomposition possible. This allows interpreters to focus on one particular component for fracture characterization at a time, so that a composite fractured reservoir could be partitioned into different components for detailed analysis. Second, curvature/flexure azimuth allows interpreters to plot fracture histogram and/or rose diagram in an automatic and quantitative manner. Compared with the conventional plotting rose diagram based on manual measurements, automatic plotting is more efficient and offers unbiased insights into fracture systems by illuminating the most likely orientations of natural fractures in fractured reservoirs.     

反正切函数拟合下的地震数据体断裂刻画方法

利用界面的形状或者其不连续性是基于叠后地震数据刻画断裂的两种主要方法,根据实际地震资料的特点,两种方法各有其优劣性.对于同界面形状相关的断裂刻画方法,较常用的为地震曲率属性.受实际断裂模型的制约,在曲率属性的基础上,曲率变化率表现出对断裂更强的相关性及敏感性.本文发展了以反正切函数为准线的柱面拟合法来刻画断裂,主要包括两个步骤,分别为:一、柱面直母线的拟合;二、柱面准线拟合及曲率变化率的求取.实际地震资料计算结果表明,该方法对断裂刻画的精度高于传统方法,能够揭示更多的断裂细节,特别是对于地震剖面上不易识别的小断距断裂,亦能够清晰的刻画,同时具有较高的信噪比.     

Arctangent function‐based third derivative attribute for characterisation of faults

Using seismic attributes such as coherence and curvature to characterise faults not only can improve the efficiency of seismic interpretation but also can expand the capability to detect faults. The coherence and curvature have been widely applied to characterising faults for years. These two methods detect faults based on the similarity of seismic waveforms and shapes of the reflectors, respectively, and they are complementary to each other and both have advantages and disadvantages in fault characterisation. A recent development in fault characterisation based on reflector shapes has been the use of the rate of change of curvature. Through an application to the seismic data from Western Tazhong of the Tarim Basin, China, it was demonstrated that the rate of change of curvature is more capable of detecting subtle faults having quite small throws and heaves. However, there often exist multiple extreme values indicating the same fault when applying the rate of change of curvature, which significantly degrades the signal‐to‐noise ratio of the computation result for multiple extrema interfering with each other. To resolve this problem, we propose the use of a linear combination of arctangent and proportional functions as the directrix of a cylindrical surface to fit the fault model and calculate its third derivative, which can then be used to characterise the fault. Through an application to the 3D seismic data from Western Tazhong of the Tarim Basin, the results show that the proposed method not only retains the same capability to detect subtle faults having small throws as the curvature change rate but also greatly improves the signal‐to‐noise ratio of the calculated result.     

Three-dimensional curvature analysis of seismic waveforms and its interpretational implications

The idea of curvature analysis has been widely used in subsurface structure interpretation from three-dimensional seismic data (e.g., fault/fracture detection and geomorphology delineation) by measuring the lateral changes in the geometry of seismic events. However, such geometric curvature utilizes only the kinematic information (two-way traveltime) of the available seismic signals. While analysing the dynamic information (waveform), the traditional approaches (e.g., complex trace analysis) are often trace-wise and thereby fail to take into account the seismic reflector continuity and deviate from the true direction of geologic deposition, especially for steeply dipping formations. This study proposes extending the three-dimensional curvature analysis to the waveforms in a seismic profile, here denoted as the waveform curvature, and investigates the associated implications for assisting seismic interpretation. Applications to the F3 seismic dataset over the Netherlands North Sea demonstrate the added values of the proposed waveform curvature analysis in four aspects. First, the capability of the curvature operator in differentiating convex and concave bending allows automatic decomposition of a seismic image by the reflector types (peaks, troughs and zero crossings), which can greatly facilitate computer-aided horizon interpretation and modelling from three-dimensional seismic data. Second, the signed minimum curvature offers a new analytical approach for estimating the fundamental and important reflector dip attribute by searching the orientation associated with least waveform variation. Third, the signed maximum curvature makes it possible to analyse the seismic signals along the normal direction of the reflection events. Finally, the curvature analysis promotes the frequency bands of the seismic signals and thereby enhances the apparent resolution on identifying and interpreting subtle seismic features.     

逆断层对致密岩石构造裂缝发育的约束控制

致密岩石(如火山岩和碳酸盐岩)可广泛发育构造裂缝,这类致密岩石的构造裂缝数值建模是构造裂缝地震解释、地震反演和油藏数值模拟的基础.我国西北各盆地普遍发育逆断层,通过在新疆巴楚地区微波塔逆断层和一间房逆断层分别布置实测剖面对野外测量的构造裂缝面密度进行定量分析,发现受逆断层控制的裂缝面密度与逆断层面的曲率呈线性关系;裂缝...     

三维多尺度体曲率的算法及应用(英文)

为了充分提取与挖掘储层结构及构造信息在时间(深度)和空间上的多尺度特征,构造了一种新的三维多尺度体曲率分析方法,并给出了三维体曲率快速提取算法。与常规的体曲率方法相比,本文方法的改进主要体现在以下两个方面:①在体曲率分析中引入时频域分频展开和对应的空间波数域多尺度自适应微分算子,可同时在时间和空间上反映地震信息的多尺度特征;②将不同尺度的体曲率数据进行有机融合,充分利用了不同尺度曲率异常信息,同时突出有效异常,降低噪声影响,为体曲率属性解释奠定基础。利用该方法处理了陆上和海上三维地震资料,实现了对储层展布、断层及裂缝发育带的检测及多尺度特征的有效刻画。     

基于局部直方图规定化的相干体增强

Coherence analysis is a powerful tool in seismic interpretation for imaging geological discontinuities such as faults and fractures. However, subtle faults or fractures of one stratum are difficult to be distinguished on coherence sections (time slices or profiles) due to interferences from adjacent strata, especially these with strong reflectivity. In this paper, we propose a coherence enhancement method which applies local histogram specification (LHS) techniques to enhance subtle faults or fractures in the coherence cubes. Unlike the traditional histogram specification (HS) algorithm, our method processes 3D coherence data without discretization. This method partitions a coherence cube into many sub-blocks and self-adaptively specifies the target distribution in each block based on the whole distribution of the coherence cube. Furthermore, the neighboring blocks are partially overlapped to reduce the edge effect. Applications to real datasets show that the new method enhances the details of subtle faults and fractures noticeably.     

Steered migration in hard rock environments

Hard rock seismic exploration normally has to deal with rather complex geological environments. These types of environments are usually characterized by a large number of local heterogeneity (e.g., faults, fracture zones, and steeply dipping interfaces). The seismic data from such environments often have a poor signal‐to‐noise ratio because of the complexity of hard rock geology. To be able to obtain reliable images of subsurface structures in such geological conditions, processing algorithms that are capable of handling seismic data with a low signal‐to‐noise ratio are required for a reflection seismic exploration. In this paper, we describe a modification of the 3D Kirchhoff post‐stack migration algorithm that utilizes coherency attributes obtained by the diffraction imaging algorithm in 3D to steer the main Kirchhoff summation. The application to a 3D synthetic model shows the stability of the presented steered migration to the presence of high level of the random noise. A test on the 3D seismic volume, acquired on a mine site located in Western Australia, reveals the capability of the approach to image steep and sharp objects such as fracture and fault zones and lateral heterogeneity.     

基于地震多属性融合的断层识别与评价——以塔里木盆地SHB地区碳酸盐岩缝洞型储层为例

塔里木盆地SHB地区的深部碳酸盐岩缝洞型储层主要发育于断裂破碎带,大多表现为断裂破碎形成的裂缝和后期溶蚀形成相互连通的断溶体.因此,断层的识别与精细评价成为该区缝洞型储层识别评价的基础.考虑到研究区处于沙漠腹部,深部地层的地震反射能量相对较弱,用单一地震属性难以实现断裂带的识别.本文针对研究区地震资料的地质-地球物理特...     

Enhancement of Seismic Data Processing and Interpretation of Fracture Zones on the Upper Part of Granitic Basement in Cuu Long Basin,Vietnam

The fractured granite basement is the primary oil and gas reservoir in the Cuu Long Basin, Vietnam. Due to the complexity of this nonlayered unconventional target, combined with complicated fault and fracture systems, the seismic data quality near and within the basement section is very low. For this reason, it is important to apply improved seismic data processing workflows, filtering and migration techniques, as wells as attribute processing methods to enhance the imaging quality.Our studies show that applying different types of filters, including the f-k, Radon transform and Tau-P, improves signal to noise ratio, removing multiples, revealing basement’s top and its related fractured and fault zones. In addition, the application of multi-arrival-solution migration algorithms, such as Kirchhoff Migration and Controlled Beam Migration, provides improved imaging for identifying basement top and faults and fractures within the basement. Furthermore, the application of seismic attributes such as curvature, apparent dip, or energy gradient, is important in locating faults and fractures, whereas mapping of intensity and orientation of such structures assists the delineation of “sweet spots” and assists the planning of exploration.     

Semi-automatic detection of faults in 3D seismic data

The semi‐automated detection of objects has been quite successful in detecting various types of seismic object, such as chimneys. The same technique can be applied successfully to detect faults in 3D seismic data. We show that several different attributes – among others, similarity, frequency and curvature, all of which potentially enhance the visibility of faults – can be combined successfully by an artificial neural network. This results in a fault ‘probability’ cube in which faults are more continuous and noise is suppressed compared with single‐attribute cubes. It is believed that the fault‐cube can be improved further by applying image‐processing techniques to enhance the fault prediction.     

基于密集台阵研究龙门山断裂带南段地震空段的地震活动性

2016年12月—2018年4月间布设于汶川、芦山地震之间地震空段的密集监测台阵(LmsSGA)提供了密集的观测数据.通过拾取地震走时、初始定位,计算地方震级,得到了完备性震级为0级的地震目录.更加完备的地震目录为地震空段及周围地震活动的时空分布特征和孕震风险性评估提供了丰富的信息.重定位结果显示地震主要集中于龙门山断裂带深度为5～20km的孕震层内.地震活动频繁的汶川、芦山主震区,震源的空间分布模式与其早期余震相似,说明两次大地震的区域仍处于缓慢的应力调整阶段.青藏高原物质东向挤出受宝兴、彭灌杂岩阻挡,在两个杂岩体西北侧地震活动频繁.地震活动性分布显示汶川—茂县、映秀—北川断裂上存在一个清晰的长约30km,宽约20km的地震活动"空白"区域,与其下方因部分熔融而产生的低速体分布一致,我们推测熔融体的加温作用是导致空段内极低的地震活动性的主要原因.监测时段内仍观测到降雨变化率和地震数量呈反相关关系,再次证实了汶川—芦山地震间地震空段及邻区内季节性降雨对地震活动性存在一定调节作用.综合分析S波速度模型、历史强震活动及b值,我们推断地震空段东部的彭灌断裂中段及周围部分隐伏断层存在发生强震的风险.     

Analysis of fault scaling relations using fault seismic attributes

We have studied three‐dimensional fault geometries through a geologically integrated analysis of fault seismic attribute volumes. We used a series of coherence (semblance) and filtered coherence attribute volumes with parameters optimised for imaging faults in the studied seismic volumes. Fault geometric attributes such as along strike segment length and displacement were measured on fault seismic attributes. The scaling relationships of fault geometric attributes were studied using statistical methods such as the Bayesian information criterion, the likelihood ratio test, and the bootstrap method. Univariate distributions of fault segment length and maximum displacement show a truncated power law for most of the fault data. The statistical results indicate a piecewise‐linear relation with two slopes between depth and fault segments lengths: depth and mean displacement. For these relations, we observe consistent increases in fault segment lengths and mean displacements from the lower tip of the fault at depth toward a point of inflection at shallower depth at the vertical section. From that point, a reduction in fault segment lengths and mean displacements toward the upper tip of the fault at the shallower depth occurs. Fault segmentation along strike increases toward the lower and upper tips of the fault, but the maximum number of segments are located near the lower tip of the fault in two of the studied faults. The fault segment length is maximum, where the number of segments (along strike) is least close to the middle of the fault in the vertical section.     

地震属性分析在高分辨率活断层地震勘探中的应用

通过分析影响地震属性的岩石物理特性及其在地震响应上的特征,获得地震波传播过程中地震振幅、层速度与裂缝层密度、泊松比、纵横波速度、孔隙度、压力的关系。同时,结合地震属性的分析技术,利用地震正演模拟的方法提高地震勘探数据解释结果精确度和可信度,为高分辨率的活断层地震勘探研究提供更为可靠的方法手段,提高了地震数据的处理解释精度。     

Integrated application of 3D seismic and microseismic data in the development of tight gas reservoirs

The development of unconventional resources, such as shale gas and tight sand gas, requires the integration of multi-disciplinary knowledge to resolve many engineering problems in order to achieve economic production levels. The reservoir heterogeneity revealed by different data sets, such as 3D seismic and microseismic data, can more fully reflect the reservoir properties and is helpful to optimize the drilling and completion programs. First, we predict the local stress direction and open or close status of the natural fractures in tight sand reservoirs based on seismic curvature, an attribute that reveals reservoir heterogeneity and geomechanical properties. Meanwhile, the reservoir fracture network is predicted using an ant-tracking cube and the potential fracture barriers which can affect hydraulic fracture propagation are predicted by integrating the seismic curvature attribute and ant-tracking cube. Second, we use this information, derived from 3D seismic data, to assist in designing the fracture program and adjusting stimulation parameters. Finally, we interpret the reason why sand plugs will occur during the stimulation process by the integration of 3D seismic interpretation and microseismic imaging results, which further explain the hydraulic fracture propagation controlling factors and open or closed state of natural fractures in tight sand reservoirs.     

Imaging pre‐existing natural fractures using microseismic data

In hydraulic fracturing treatments, locating not only hydraulic fractures but also any pre‐existing natural fractures and faults in a subsurface reservoir is very important. Hydraulic fractures can be tracked by locating microseismic events, but to identify the locations of natural fractures, an additional technique is required. In this paper, we present a method to image pre‐existing fractures and faults near a borehole with virtual reverse vertical seismic profiling data or virtual single‐well profiling data (limited to seismic reflection data) created from microseismic monitoring using seismic interferometry. The virtual source data contain reflections from natural fractures and faults, and these features can be imaged by applying migration to the virtual source data. However, the imaging zone of fractures in the proposed method is strongly dependent on the geographic extent of the microseismic events and the location and direction of the fracture. To verify our method, we produced virtual reverse vertical seismic profiling and single‐well profiling data from synthetic microseismic data and compared them with data from real sources in the same relative position as the virtual sources. The results show that the reflection travel times from the fractures in the virtual source data agree well with travel times in the real‐source data. By applying pre‐stack depth migration to the virtual source data, images of the natural fractures were obtained with accurate locations. However, the migrated section of the single‐well profiling data with both real and virtual sources contained spurious fracture images on the opposite side of the borehole. In the case of virtual single‐well profiling data, we could produce correct migration images of fractures by adopting directional redatuming for which the occurrence region of microseismic events is divided into several subdivisions, and fractures located only on the opposite side of the borehole are imaged for each subdivision.     

基于离心窗倾角扫描的曲率属性提取

体曲率属性作为三维地震资料构造解释的重要工具,在识别地层弯曲、地层不连续性,以及裂缝预测方面呈现了不可或缺的作用,因此如何高质量的提取该属性成为一个需要关注的问题.体曲率属性提取质量的关键在于倾角扫描的精度,本文提出了一种基于离心窗的倾角扫描方法,该离心窗是在空间为中心偏离分析点的四个旋转窗口,时间上为包含分析点的五个纵向滑动窗口,通过变换不同的窗口进行高精度倾角估计,并采用最小二乘拟合插值求取真实倾角.该方法避免了多窗扫描对小断层构造的忽略以及噪声的过大影响,同时在处理中对倾角数据进行中值滤波,去掉噪点影响.将由离心窗倾角扫描方法所计算的倾角数据体应用到曲率属性的计算中,在恢复构造细节和提高信噪比方面均展现了较好的效果.     

复杂断块精细构造解释技术与效果

以大芦家地区为例详细论述了复杂断块精细构造解释的方法和流程.对地震资料的选取、层位标定、断裂系统识别与组合、层位立体解释及构造成图每个步骤的方法给以具体论述,重点分析了三维精细构造解释使用的关键技术如时变子波标定技术、相干体技术、变速成图技术.在实际应用中取得了良好的效果.     

Joint exploration of crustal structure in Fuzhou basin and its vicinities by deep seismic reflection and high-resolution refraction as well as wide-angle reflection/refraction

~~Joint exploration of crustal structure in Fuzhou basin and its vicinities by deep seismic reflection and high-resolution refraction as well as wide-angle reflection/refraction1.Ma,X.Y.,The Atlas of Lithospheric Dynamics of China(in Chinese),Beijing:Atlas Publishing Company,1989,1-68. 2.Liao,Q.L.,Wang,Z.M.,Wang,P.L.et al.,Explosion-generated earthquake study on crustal deep structure in Fuzhou-Quanzhou-Shantou region,Acta Geophysica Sinica(in Chinese),1988,31(3):270-280. 3.L…