Seismic Horizon Skeletonization

Abstract

Method for analysis of hydrocarbon potential of subterranean regions by generating surfaces or geobodies and analyzing them for hydrocarbon indications. Reflection-based surfaces may be automatically created in a topologically consistent manner where individual surfaces do not overlap themselves and sets of multiple surfaces are consistent with stratigraphic superposition principles. Initial surfaces are picked from the seismic data ( 41 ), then broken into smaller parts (“patches”) that are predominantly topologically consistent ( 42 ), whereupon neighboring patches are merged in a topologically consistent way ( 43 ) to form a set of surfaces that are extensive and consistent (“skeleton”). Surfaces or geobodies thus extracted may be automatically analyzed and rated ( 214 ) based on a selected measure ( 213 ) such as one or more direct hydrocarbon indications (“DHI”), e.g. AVO classification. Topological consistency for one or more surfaces may be defined as no self overlap plus local and global consistency among multiple surfaces ( 52 ).

1 . A computer-implemented method for transforming a seismic data volume acquired in a seismic survey to a corresponding data volume which, when visually displayed, shows a representation of subterranean reflector surfaces that gave rise to the data by reflecting seismic waves, said method comprising:
 (a) picking seismic reflections from the data volume, and creating initial surfaces from the picks;   (b) breaking surfaces into smaller parts (“patches”) that are predominantly topologically consistent;   (c) merging neighboring patches in a topologically consistent way, thus extracting topologically consistent reflection-based surfaces from the seismic data volume; and   (d) displaying the extracted surfaces for visual inspection or interpretation, or saving their digital representations to computer memory or data storage.   
     
     
         2 . The method of  claim 1 , further comprising using the topologically consistent reflection-based surfaces to predict or analyze potential for hydrocarbon accumulations. 
     
     
         3 . The method of  claim 1 , wherein topologically consistent comprises verifying that surfaces satisfy at least one of (i) no self overlaps; (ii) local consistency; and (iii) global consistency. 
     
     
         4 . The method of  claim 1 , wherein the seismic reflections are picked by correlating reflection events between neighboring traces in the seismic data volume. 
     
     
         5 . The method of  claim 4 , wherein the picking is automated, using a computer. 
     
     
         6 . The method of  claim 1 , wherein breaking surfaces into patches comprises shrinking initial surfaces to lines, removing joints in the lines to form more individual lines, shrinking individual lines to single-voxel points (characteristic points), and propagating the characteristic points along the initial surfaces by adding neighboring voxels to form patches of voxels. 
     
     
         7 . The method of  claim 6 , wherein each characteristic point is labeled with a different label, and the label is applied to the patch formed around the characteristic point, thus providing a means to keep track of different patches as they are expanded by propagation. 
     
     
         8 . The method of  claim 6 , wherein controlled marching is used to propagate points along initial surfaces. 
     
     
         9 . The method of  claim 6 , wherein shrinking of an initial surface to a line comprises successively removing one-voxel-thick layers from the periphery of the surface until a continuous line of individual voxels results. 
     
     
         10 . The method of  claim 6 , further comprising deleting joint voxels from lines to form more lines before shrinking lines to points. 
     
     
         11 . The method of  claim 6 , wherein topological consistency is enforced during the propagation of points. 
     
     
         12 . The method of  claim 1 , wherein merging neighboring patches in a topologically consistent way is performed by developing overlap and neighbor tables for the patches, generating an order for merge pair candidates by sorting the overlap and neighbor tables, checking candidate merges for topological consistency using the overlap and neighbor tables, and accepting topologically consistent mergers. 
     
     
         13 . The method of  claim 12 , wherein the sort order of the neighbor table is based on geometries of, or geometry differences between, the neighboring patches, or is based on the statistical properties of, or the differences between, one or more attributes extracted from seismic data collocated with the patches. 
     
     
         14 . The method of  claim 1 , further comprising spatially flattening the topologically consistent reflection-based surfaces into an order representing the sequence of deposition using the topologically consistent reflection-based surfaces and using the flattened surfaces to predict or analyze potential for hydrocarbon accumulations. 
     
     
         15 . The method of  claim 14 , further comprising flattening the associated seismic data within which the topologically consistent reflection-based surfaces exist. 
     
     
         16 . The method of  claim 15 , wherein the seismic data flattening is performed by nonlinear stretch of the seismic data or by a cut and past method. 
     
     
         17 . The method of  claim 1 , further comprising creating a visual representation showing depositional order or hierarchy of the topologically consistent reflection-based surfaces. 
     
     
         18 . The method of  claim 17 , further wherein the visual representation is a tree and comprising using the tree to select one or more surfaces for visualization. 
     
     
         19 . The method of  claim 1 , further comprising using the patches to segment the seismic data volume into three-dimensional bodies or inter-surface packages that represent geologic units that were deposited within a common interval, and using them to analyze for hydrocarbon potential. 
     
     
         20 . The method of  claim 2 , further comprising analyzing the location and characteristics of edges and termination points of the topologically consistent reflection-based surfaces and using that to assist in predicting or analyzing potential for hydrocarbon accumulations. 
     
     
         21 . The method of  claim 2 , further comprising analyzing attributes and geometric characteristics of the topologically consistent reflection-based surfaces and/or the associated seismic data at the locations of said surfaces to assist in predicting or analyzing potential for hydrocarbon accumulations. 
     
     
         22 . The method of  claim 1 , further comprising using the patches or topologically consistent reflection-based surfaces to reduce the amount of information contained in the seismic data volume in order, thereby reducing storage or computational efficiency requirements for subsequent data processing of the seismic data. 
     
     
         23 . The method of  claim 1 , wherein merging neighboring patches is restricted to patches that trace back before shrinking to the same initial surface. 
     
     
         24 . The method of  claim 12 , wherein topological consistency is enforced in merging neighboring patches using a depth-limited search method comprising:
 (a) creating a graph structure based on the overlap table that captures relative positions of the patches in the data volume;   (b) assigning a depth attribute to each patch such that comparison of the depth attributes of any two patches indicates whether one of the patches overlies the other;   (c) using the graph structure and the depth attributes to check a merger proposed based on the neighbor table for topological consistency; and   (d) updating the depth attributes and graph structure as patch mergers are accepted.   
     
     
         25 . The method of  claim 1 , wherein the extracted surfaces are displayed or saved as an earth model. 
     
     
         26 . A computer program product, comprising a computer usable medium having a computer readable program code embodied therein, said computer readable program code adapted to be executed to implement a method for reducing a seismic data volume to reflection-based surfaces, said method comprising:
 (a) picking seismic reflections from the data volume, and creating initial surfaces from the picks;   (b) breaking surfaces into smaller parts (“patches”) that are predominantly topologically consistent; and   (c) merging neighboring patches in a topologically consistent way, thus extracting topologically consistent reflection-based surfaces from the seismic data volume.   
     
     
         27 . A method for producing hydrocarbons from a subsurface region, comprising:
 (a) obtaining a seismic data volume representing the subsurface region;   (b) obtaining a prediction of the potential for hydrocarbon accumulations in the subsurface region based at least partly on topologically consistent reflection-based surfaces extracted from the seismic data volume by a method described in  claim 1 , which is incorporated herein by reference; and   (c) in response to a positive prediction of hydrocarbon potential, drilling a well into the subsurface region and producing hydrocarbons.   
     
     
         28 . A method for merging surfaces identified in a seismic or seismic attribute data volume to form larger surfaces representing subterranean geologic structure or geophysical state of matter, comprising merging neighboring surfaces in a topologically consistent way. 
     
     
         29 . A method for exploring for hydrocarbons, comprising:
 (a) obtaining a data volume of seismic or seismic attribute data resulting from a seismic survey;   (b) subdividing the data volume into parts, called objects;   (c) forming regions of one or more objects;   (d) developing or selecting a measure for ranking the regions in terms of potential to represent a geobody, interface surface, or intersection of these, or other physical geologic structure or geophysical state of matter that is indicative of hydrocarbon deposits; and   (e) using the measure to prioritize regions, and then using the prioritization to assess the volume for hydrocarbon potential.   
     
     
         30 . The method of  claim 29 , wherein each object contains cells classified together using one or more criteria based on the data or attribute thereof or other physical reasonableness criterion. 
     
     
         31 . The method of  claim 29 , further comprising using the region prioritization to transform the data volume into a geophysical earth model, and using the earth model to assess the volume for hydrocarbon potential. 
     
     
         32 . The method of  claim 29 , wherein (b) is performed using a method described in  claim 1 , which is incorporated herein by reference. 
     
     
         33 . The method of  claim 29 , wherein the measure in (d) comprises a direct hydrocarbon indicator (DHI).