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Hunt L.,Fairborne Energy | Reynolds S.,Fairborne Energy | Brown T.,Fairborne Energy | Hadley S.,Fairborne Energy | And 2 more authors.
Leading Edge (Tulsa, OK) | Year: 2010

These experiments illustrate that the AVAZ, VVAz, and curvature attributes correlate strongly with image log fracturedensity, and should be valid predictors of fractures in the Nordegg of this area. Similar observations were made using the microseismic data, a less direct validator of fracture prediction, also exhibited strong correlations. The large,spatially distributed sample size and similar support make microseismic events an intriguing data element to compare and cross-validate with surface seismic fracture predictors. The comparison of microseismic to surface seismic should be carried out with other data to determine if the results are repeatable. Further experiments may reveal how important the wellbore orientation and hydraulic fracture orientation were with reference to hmax and the orientation of the preexisting natural fractures. This work indicated that AVAz was the best single predictor of fracture density, although curvature attributes were almost as good. We also observed that despite the predictive correlations, significant scatter remained in the data comparisons. That scatter likely has implications to our data quality as well as the theoretical limitations of our methods. In consideration of this, we attempted to use com binations of the attributes in multilinear and crossplotting approaches. These results were most accurate when AVAz and curvature were used together. The advantage of using these attributes together may lie in the areas of validity for each attribute: AVAz can directly detect fractures, but may fail in hinge zones where multiple fracture sets are most likely to exist, while the curvature attribute identifies the hinge zones, but may not infer the fractures that exist in less obviously deformed areas. A surprising conclusion from this work was that the coherence attribute did not predict fracture density or microseismic event moments for the Nordegg in this area. For the kinds of fractures that exist in the Nordegg of this area, AVAz and curvature are a more useful combination than coherence and curvature, which have been used to advantage in other areas. © 2010 Society of Exploration Geophysicists.

Chopra S.,Arcis Corporation | Chopra S.,University of Oklahoma | Marfurt K.J.,University of Oklahoma
Leading Edge (Tulsa, OK) | Year: 2010

Volumetric curvature is a well-established interpretational tool that allows us to image subtle faults, folds, incised channels, differential compaction, and a wide range of other stratigraphic features. The maximum and minimum curvatures define the eigenvalues of a quadratic surface. By definition (and based on eigenstructure analysis), the maximum curvature is defined as the principal curvature that has the larger absolute value. We find that the principal curvatures k1 and k2, where k1 ≥ k2, provide the simplicity of interpretation seen in kpos and kneg, but retain the robustness of kmax and k min in the presence of steep dip. Multispectral volumetric curvature attributes are valuable for prediction of fracture lineaments in deformed strata. Several applications of volume curvature have been completed in different geological settings, which are useful for different stratigraphic features, ranging from imaging of channel boundaries and small scale faults to highly fractured zones. Corendering volumetric curvature with coherence provides a particularly powerful tool. © 2010 Society of Exploration Geophysicists.

Chopra S.,Arcis Corporation | Hardage B.,University of Texas at Austin
Leading Edge (Tulsa, OK) | Year: 2010

Borehole geophysics is essential for exploration, assessment, and production of Earth's resources, in addition to carrying out fundamental studies on the Earth itself. Borehole-based technology encompasses activities ranging from coring to measurements such as logging, VSP, crosswell profiling, and passive seismic monitoring. Each of these disciplines has grown into an established branch of borehole geophysics. The idea behind all these measurements has been to obtain useful information about the geological environment that helps evaluate subsurface zones of interest. © 2010 Society of Exploration Geophysicists.

Hunt L.,Fairborne Energy Ltd | Reynolds S.,Fairborne Energy Ltd | Hadley S.,Fairborne Energy Ltd | Downton J.,CGGveritas | Chopra S.,Arcis Corporation
Leading Edge (Tulsa, OK) | Year: 2011

We propose scaling volume curvature measurements with material property estimates to produce a superior prediction of natural fractures. Curvature is one of many, indirect, fracture-inferring attributes. It does not detect fractures, but is causally related to them through the assumption that increasing curvature relates to increasing strain. There are many other variables that are causally related to fractures. We propose that it would be advantageous to create combinations of these causal variables with curvature. Some of the most well known and important causes of variations in natural fracture density are material properties relating to brittleness. Material properties are critical geologically at all scales, from large-scale regional studies to prospect-level inquiries because the properties may vary significantly within individual formations and between formations. These vertical and lateral changes in material properties may be important and should be considered in fracture estimation, along with curvature. There is a lack of clarity regarding exactly which material property is best from the perspective of physics and rock mechanics; however, we have chosen a combination of parameters that we argue is a starting point. Fortunately, material properties are routinely estimated with amplitude variation with offset (AVO) techniques, and there is little practical reason not to use them together with curvature to produce a more complete attribute inferring fracture density. The combination of these variables is a step in the direction of creating quantitative causal fracture prediction estimates. © 2011 Society of Exploration Geophysicists.

Chopra S.,Arcis Corporation | Marfurt K.J.,University of Oklahoma
SEG Technical Program Expanded Abstracts | Year: 2011

Over the last several years, seismic curvature attributes have been shown to be very useful in delineation of folds, flexures, and faults. Although many curvature measures have been introduced we find the most-positive and most-negative principal curvatures k1 and k2 to be the most useful. All other curvature measures can be derived from the two principal curvatures. For example, Hart (2002) and others have found the components of apparent curvature projected parallel to the dip azimuth and strike of a dipping plane to be useful in given tectonic and stress settings. In this study we describe the theory and application of Euler curvature, which is a generalization of the dip and strike components of curvature in any user-defined direction, to the interpretation of surface seismic data. This attribute is useful for the interpretation of lineament features in desired azimuthal directions, say, perpendicular to the minimum horizontal stress. If a given azimuth is known or hypothesized to be correlated with open fractures or if a given azimuth can be correlated to enhanced production or effective horizontal drilling, an Euler-curvature intensity volume can be generated for that azimuth thereby high-grading potential sweet spots. © 2011 Society of Exploration Geophysicists.

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