The effect of preexisting joints on normal fault evolution : insights from fieldwork and analogue modeling

Huge hydrocarbon reservoirs worldwide are bound to brittle lithologies that are affected by interacting fracture networks. For a better prediction of reservoir qualities a basic investigation of such interactions is inevitable. In this context, the present work aims for an understanding of the effect of preexisting joint sets on normal fault evolution. Approaches for this work contain a field study, remote sensing and analogue modeling. The Grabens Area of the Needles fault zone in the Canyonlands National Park, Utah/USA was chosen as field analogue. This arcuate array of young grabens (younger than SI{100}{ka}) extends over several kilometers along the Colorado River in Permian brittle lithologies with distinct preexisting joint sets. The graben-bounding normal faults formed due to gravity-driven extension above Pennsylvanian evaporites. The well-preserved outcrops and the stratigraphic similarity to producing reservoirs make this region a perfect field analogue. Remote sensing included geographic information system (GIS)-based mapping of over 20,000 joints and 500 faults from high resolution orthoimagery as well as calculations of drainage pattern and dip directions from digital elevation models. During field work, classic geologic field methods were used as well as a handheld laser distance measurement device and ground penetrating radar (GPR) surveys. For the analogue modeling cohesive and very fine-grained hemihydrate powder was used that scales well for brittle lithologies. Analytic methods contain high resolution time-lapse photography and particle imaging velocimetry (PIV) analyses. The GIS analyses revealed a correlation between joint and fault orientation. Interpreting the graben floor dips yielded evidence for both dipping as a result of oriented sedimentation and dipping due to different displacements at the graben bounding faults. Field observations at graben crosscuts confirm this assumption. Sinkholes, mapped in airborne imagery and in the field, indicate a steep-dipping dilational faulting close to the surface. This is consistent with the observation that graben walls coincide with original joint surfaces without slickenlines or toolmarks. Additional measurements of heave and throw allowed to estimate fault dips at depth which were then applied to an extensional model through the northern grabens, aiming to quantify the total extension. The GPR surveys worked well for the upper SI{10}{m} of sediment and the interpreted profiles imply an ongoing horizontal extension as well as in some cases changing rates of displacement or sedimentation. XRD and thinsection analysis of a calcite sample, derived from a fault/joint-interface, gave additional evidence for dilational faulting. Analogue models finally confirmed the findings of field work and GIS analysis and came up with very similar structures and features. It could be shown that preexisting joint-sets do affect normal fault geometries distinctly, although more work is needed to quantify this relationship in detail.

Grantor dc:publisher

Publikationsserver d. RWTH Aachen Univ.

Year dc:date

2012

Author dc:creator

• Kettermann, Michael

• info:eu-repo/classification/ddc/550
• Abschiebung <Geologie>
• Canyonlands National Park
• Klüftung
• Kluft
• Graben
• Störung <Geologie>
• Endogene Dynamik
• Strukturgeologie
• Elektromagnet
• Geowissenschaften
• Analoge Modellierung
• joint
• fault
• analogue modeling
• interaction
• canyonlands

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

eng

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-112358%22

OAI record oai:identifier

https://publications.rwth-aachen.de/oai2d?verb=GetRecord&metadataPrefix=oai_dc&identifier=oai%3Apublications.rwth-aachen.de%3A48762