The chapter also introduces important tools and concepts commonly employed in seismic data interpretation that include seismic sequence stratigraphy, seismic facies analysis, and direct hydrocarbon indicators (DHIs). Such structural features that are of interest to petroleum exploration include faults, folds, and diapirs and the chapter discusses relevant aspects of these features. Structural features are generally easy to identify in seismic sections. This chapter provides an overview of important structural and stratigraphic features commonly observed in exploration seismic images. The principal curvatures K1 and K2 are calculated from the intersection of the circle with the kn axis. A least squares best fit circle is fitted through the four points and the centre used to position the kn axis. The principal curvatures lie in directions of no surface torsion. The procedure for calculating normal curvatures and surface torsion is described in Lisle & Robinson (1995). (c) The Mohr circle construction allows plotting of the data points in normal curvature (kn) versus surface torsion (tg) space without prior knowledge of the position of the kn axis. The curvatures are then plotted on a Mohr circle diagram. Curvature is the reciprocal of the radius and is calculated for each set of A-A', B-B', C-C' and D-D'. The curvature is calculated by fitting an arc of a circle through the three points, finding the coordinates of the centre and calculating the radius of the circle. Curvature is measured on four vertical planes through the central node and opposite pairs. (a) Plan view of arrangement of a node with its eight nearest neighbours. However, care must be taken to separate intrinsic and tectonic curvatures when generating and interpreting k λ plots and their integrals.įeatures of the algorithm for calculating curvature from gridded data points. Freeing algorithms from the restriction of the ‘arbitrarily’ selected minimum grid node spacing is a key step towards calibrating measured curvature against strain mechanisms. The k λ integral provides a relatively simple approach to calculating the degree of multi-wavelength strain present at a particular grid node. A range of alternative types of curvature and curvature spectra are compared with other approaches to curvature calculation and other factors relevant to the calibration of such techniques in terms of the distribution of brittle fractures in sedimentary rocks. This algorithm has been tested using data from several North Sea chalk fields. Further filters designed to screen the effects of background tectonic, or non-tectonic, curvatures can be applied to the k λ integral. Portions of these data can be collapsed into single values by calculating the integral of the k λ curve. They also deliver intermediate wavelength features such as fault drag or buckle folding and the identification of long-wavelength (basin-scale) curvatures. These ‘spectral’ or k λ plots can be generated for each grid node and allow the definition of short-wavelength, high-amplitude noise cut-off lengths. The algorithm has also been used to generate plots of summed absolute curvature as a function of grid node separation ( k versus λ). For any grid node, the algorithm calculates the magnitude and orientations of the two principal curvatures, K 1 and K 2, from which other curvature measurements can be derived, such as Gaussian curvature and summed absolute curvature ( K 1 + K 2 ). Here we describe the development of an algorithm for measuring the curvature of gridded surfaces derived from seismic data. In many hydrocarbon reservoirs, this strain is expressed as brittle fracturing that may significantly impact reservoir performance. The curvature of structured geological surfaces can be used to assess the degree of strain they have undergone.
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