Structural Styles in Seismic

Structural Styles Brenton, David, & Ryan

Normal-fault related structures

Syncline formed by growth faulting Shear fold formed as fault tip displacement was lost near the surface

Nigeria profile Normal-fault

related structures

Cretaceous strata onlap

Jurassic faulting

Syncline formed by growth faulting

Fault arrays under the Browse Basin

NW continental margin of Australia Mostly normal throws - partial inversion on the NW side of section? Post breakup unconformity overlain by strata that onlap significant relief across the section

Normal-faulted clinoforms, offshore Namibia

Thrust-Related Structures: Buckle folded Messinian strata, Western Ionian

Imbricate Thrust System:Glacial thrust belt, Danish North Sea

Toe of the Delta Thrust Faults, Deep Water Niger Delta

Connors, 2009

Flower Structures

Positive Flower

Negative Flower

Fault Imaging Challenges •

Juxtaposition of different velocity rocks causes issues with seismic profiles.

•

Ex: Thrust faults-faster velocity rocks over slower rocks o

•

Salt Intrusions

Planar faults appear curved o

o

velocity increases with depth constant thickness of rocks represented by smaller TWT at depth than shallower

Case Study: LLanos Foothills, Columbia Located between Eastern Cordillera and the undeformed foreland basin

Exploration in the mid 90's led to the discovery of 2 major fields: Cusiana and Cupiagua BPXC - 2000km 2D sesimic - 800km2 3D Estrada & Jaramillo (2003)

Columbia

Modeling showed long tails generated by overturned thrust sheets Post stack migration caused reflectors beneath the thrust sheets to be broken up

Reprocessing

3D seismic Quality of 2D lines was seen as adequate for the appraisal of the Cusiana.

Wasn't possible to define the limits of the Cupiagua field 3D acquisition resulted in "stepchange" in data quality

Seismic Attributes •

An attribute is a measured characteristic taken from seismic data •

•

Can reveal features that could easily be missed and aid in interpretation

Especially important in imaging complex fault systems •

For faults the two most important attributes are coherency and volumetric curvature

Coherency •

The measure of similarity between traces in a small analysis window

Coherency Cube

References Bahorich, Mike, and Steve Farmer. "3-D Seismic Discontinuity for Faults and S tratigraphic Features: The Coherence Cube: ABSTRACT." The Leading Edge (1995): 1053-058.

Connors, C. D., B. Radovich, A. Danforth, and S. Venkatraman. "The Structure of the Offshore Niger Delta." Orsget  (2009): 182-88.

Estrada, C. A., & Jaramillo, J. A. (2003). Making the difference: A story of pitfalls and successes in seismic imaging in a thrust belt environment.

Nissen, Susan. Using 3-D Seismic Attributes in Reservoir Charaterization. 9 Aug. 2007. Presentation. Hays, KS.

Virtual Seismic Atlas, http://see-atlas.leeds.ac.uk:8080/home.jsp