A new analytical method for azimuthal curvature analysis from 3D seismic data (original) (raw)
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GEOPHYSICS, 2015
Fracture characterization is fundamental to the reliable prediction of fractured reservoirs; however, it is difficult and expensive to obtain detailed fracture information required for reservoir prediction due to the lack of direct observational data in the subsurface. Here we develop seismic analysis methods to characterize fractured reservoirs based on reflection geometry related to bending and shearing of reservoir formations. Among various geometric attributes, we focus on extreme curvature and extreme flexure that are considered effective at detecting fractures. Extreme curvature refers to the signed absolute maximum curvature at a specific azimuth where the curve shape is the tightest, whereas extreme flexure refers to the signed absolute maximum gradient of curvature at a specific azimuth where the curve shape changes the most. We implement new algorithms based on analytical equations to calculate extreme curvature and extreme flexure along with the corresponding azimuth from 3D seismic data. Results from 3D seismic surveys demonstrate that the new algorithms help resolve structural details that are otherwise not easily discernible from regular amplitude and conventional attributes. Most importantly, the algorithms hold the potential to volumetrically detect and visualize fractures in an automatic and quantitative manner. We conclude that extreme curvature and extreme flexure attributes have important geologic implications for predicting fundamental fracture properties that are critical to fractured reservoir characterization in the subsurface.
Geophysical Prospecting, 2015
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.
Fracture characterization is critical to reliable prediction of fractured reservoirs. Fractures formed by folding and/or shearing of reservoir formations, can be detected using seismic curvature and flexure analysis. Previous curvature and flexure analysis methods often have limitations in accuracy and efficiency in the presence of structural dip. We have developed new algorithms for volumetric curvature and flexure analysis based on 3D surface rotation using the local reflector dip to improve the accuracy and efficiency for curvature and flexure analysis in structurally complex settings. Among the various measures of curvature and flexure in 3D space, we have focused on signed maximum curvature and flexure that are considered to be most effective for predicting intensity and orientation of faults and fractures in fractured reservoirs. The application of the algorithms to a 3D seismic survey from Teapot Dome (Wyoming) demonstrated that the new methods help resolve subtle structural details that are otherwise not easily discernible from regular amplitude and conventional attributes, thus enhancing our capability to visualize and understand the structural complexity of fractured reservoirs.
GEOPHYSICS, 2006
Volumetric curvature analysis is a simple but computationally intensive procedure that provides insight into fracture orientation and regional stresses. Until recently, curvature analysis has been limited to computation along horizon surfaces that may be affected by unintentional bias and picking errors introduced during the interpretation process. Volumetric curvature is best estimated in a two-step process. In the first step, we use a moving-analysis subvolume to estimate volumetric reflector dip and azimuth for the best-fit tangent plane for each sample in the full volume. In the second step, we calculate curvature from adjacent measures of dip and azimuth. We use larger curvature analysis windows to estimate longer wavelength curvatures. Such a technique allows us to output full 3D volumes of curvature values for one or more scales of analysis. We apply these techniques to a data set from the Central Basin Platform of west Texas and find lineaments not observable with other seis...
A new algorithm for evaluating 3D curvature and curvature gradient for improved fracture detection
Computers & Geosciences, 2014
In 3D seismic interpretation, both curvature and curvature gradient are useful seismic attributes for structure characterization and fault detection in the subsurface. However, the existing algorithms are computationally intensive and limited by the lateral resolution for steeply-dipping formations. This study presents new and robust volume-based algorithms that evaluate both curvature and curvature gradient attributes more accurately and effectively. The algorithms first instantaneously fit a local surface to seismic data and then compute attributes using the spatial derivatives of the built surface. Specifically, the curvature algorithm constructs a quadratic surface by using a rectangle 9-node grid cell, whereas the curvature gradient algorithm builds a cubic surface by using a diamond 13-node grid cell. A dip-steering approach based on 3D complex seismic trace analysis is implemented to enhance the accuracy of surface construction and to reduce computational time. Applications to two 3D seismic surveys demonstrate the accuracy and efficiency of the new curvature and curvature gradient algorithms for characterizing faults and fractures in fractured reservoirs.
explora t ion review InterpretIng fractures through 3 D seIsmIc
2009
Characterization of fractures is essentially the understanding of fracture patterns, so that appropriate ways can be devised for effectively producing fractured reservoirs. The presence of naturally occurring fracture networks can lead to unpredictable heterogeneity within many reservoirs. Alternatively, fractures provide high permeability pathways that can be exploited to extract reserves stored in otherwise low permeability matrix rock. Consequently, the detection and characterization of fractures, which is driving significant improvements in azimuthal AVO, image-log breakout interpretation, and seismic attribute analysis, is of great interest. Surface seismic data has long been used for detecting faults and large fractures, but recent developments in seismic attribute analysis have shown promise in identifying groups of closely spaced fractures or interconnected fracture networks. EXPLORATION REVIEW photo overleaf Strata-cube slice from the maximum curvature attribute run on the seismic amplitude data. Besides the main faults running northeast-southwest, many fractures can be seen on the slice. Image courtesy arcIs , 2009 Fractures can enhance permeability in reservoirs and hence impact the productivity and recovery efficiency from them. Fold and fault geometries, stratal architecture and large-scale depositional elements (e.g. channels, incised valley-fill and turbidite fan complexes) are often difficult to see clearly on vertical and horizontal slices through seismic reflection data. Seismic discontinuity attributes help us in characterizing stratigraphic features that may comprise reservoirs and form an integral part of most interpretation projects completed today. Coherence and curvature are two important seismic attributes that are used for such analysis. However, for extracting accurate information from seismic attributes, the input seismic data needs to be conditioned optimally. This includes noise removal, using robust dip-steering options and superior algorithms for computation of seismic attributes. Curvature attributes, in particular, exhibit detailed patterns for fracture networks that can be correlated with image logs and production data to ascertain their authenticity. One way to do this correlation is to manually pick the lineaments seen on the curvature displays for a localized area around the borehole, and then transform these lineaments into rose diagrams to compare with similar rose diagrams obtained from image logs. Favourable comparison of these rose diagrams lends confidence in the interpretation of fractures. An alternative
3D curvature analysis of seismic waveforms and its interpretational implications
Geophysical Prospecting
The idea of curvature analysis has been widely used in subsurface structure interpretation from three-dimensional (3D) 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 analyzing 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 3D 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 3D 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 analyze 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.
Interesting directions being pursued in seismic curvature attribute analysis
SEG Technical Program Expanded Abstracts 2012, 2012
Seismic curvature attribute analysis forms an integral part of most interpretation projects as they yield useful information that adds value for the interpreters. Being a popular tool, curvature applications are expanding in terms of not only different types of curvature measure but also in terms of their visualization, their application on other types of data besides seismic amplitudes, and scaling curvature with other attributes so as to extract more useful information. In this work we discuss the different developments and their applications.