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Analyzing and Interpreting Geologic Structure with Automatic Fault Extraction - Rock & Fluid Canvas 2009 | Epos 4 Paradigm AFE New Features
Fault-stick interpretation has long been a mainstay of the work of the seismic interpreter. In the past this was accomplished by tedious picking of either one or several faults at a time on an evenly spaced subset of the lines or crossline vertical seismic amplitude sections. The advent of Coherence Cube in the mid 1990s made the process easier to check for errors such as crossing fault relays, or incorrectly joining intersecting faults, and in some cases made it easier to understand the relationship of cross-cutting faults in determining relative fault timing. However, fault interpretation still primarily consisted of manual picking on a subset of lines, crosslines or z-slices.
Automatic Fault Extraction (AFE), introduced by Paradigm* in 2006, reduced the tedium of the slice to slice interpretation and enabled the seismic interpreter to quickly pick hundreds of faults at a time. Faults were now automatically picked in all 3 dimensions and the task of the interpreters changed from spending most of the available time making the picks to editing and interpreting the results of the automatic picks.
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Fig. 1: Fault Enhanced Volume with Planar Clustered Faults –
Gulf of Mexico dataset. |
In the Rock & Fluid Canvas™ 2009 release, AFE has undergone significant changes to make the editing and interpretation of the results easier and faster. All faults are now named according to their strike and dip orientations which enables the interpreter to quickly sort on loading or in the display so that one major orientation at a time can be identified, turned on or off, copied to an interpretation list or geoset, or have all faults of the group displayed with the same display properties. The fault segments now more closely track the discontinuities than in previous versions of AFE because of better enhancement processing of the coherence input data. The better-enhanced coherence data is now immediately available as an Epos brick file to assist even in a manual fault interpretation process.
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Fig. 2: Fault Enhanced mid-Cretaceous time slice w/ Rose
diagram Analysis showing primary(blue), secondary(green)
, and tertiary(black) structural orientations--Australia dataset. |
New analysis capabilities are also included in the new Rock & Fluid Canvas 2009 version of AFE. A Rose diagram allowing independent statistical analysis of the automatically extracted lineaments is useful to the structural interpreter in understanding fault orientations relative to different areas or different geologic ages (based on marker horizons). A statistical analysis of the lineaments is also available to study fractured plays such as the Barnett shale. The lineaments are also presented in a new volume (the vector azimuth volume) in which the direction of each lineament is presented as the value along the lineament while the rest of the non-extracted data remains undefined. This volume can be viewed separately or co-rendered with amplitude or coherence data to enhance understanding of the stress orientations.
One of the results of improved lineament tracking is that many more faults are extracted than in prior versions. Single geologic faults are often represented by numerous separate AFE faults which need to be joined together in order to create a meaningful surface. The joining of these faults can be readily accomplished using standard interpretation tools that reassign fault segments to another fault, or that build a single T-surface with multiple different faults as input. In Rock & Fluid Canvas 2009, we provide a new tool in AFE to automatically cluster the constituent faults into a single surface. The Planar Clustering feature, which uses a separate license, allows the user to select which faults potentially may be clustered together. The process reduces the total number of fault “pieces” for the individual geologically significant faults using a different algorithm than the initial fault linkage algorithm. For example the user might select 700 faults with NNW strike and West dip as output from the initial fault linkage step and the planar cluster process may reduce that to 75 NNWstrike, West dip faults.
The new AFE adds some powerful tools to the structural interpreter’s toolbox. Faults are better quality and much easier to work with than faults generated with earlier versions of software, allowing the interpreter to spend more time with structural interpretation analysis activities rather than tedious fault picking activities.
*AFE is a joint development of TerraSpark Geosciences and Paradigm.
Laura Evins
Senior Geophysicist
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