Serial Cross-Section Trishear Modeling: Reconstructing 3-D Kinematic Evolution of the Perdido Fold Belt* Dian He 1 and John Paul Brandenburg 2 Search and Discovery Article #30313 (2014)** Posted January 20, 2014 *Adapted from oral presentation given at AAPG Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013 **AAPG 2013 Serial rights given by author. For all other rights contact author directly. 1 Department of Geology and Geophysics, Louisiana State University, Baton Rouge, LA (dhe2@lsu.edu) 2 Shell International Exploration and Production, Houston, TX Abstract Fault interpretations in seismic data wipe-out zones are commonly non-unique, particularly in contractional structures. This consequently leads to increased risk in hydrocarbon exploration. Trishear modeling provides a quantitative method to constrain the geometries and locations of faults in wipe-out zones using the data set of horizons interpreted from well-imaged areas. Here, we examine a pair of opposing fault propagation folds in the Perdido Fold Belt, northwest Gulf of Mexico. The two opposing fault zones are poorly imaged in seismic data. However, some geometric observations such as footwall thickening and well imaged hanging wall anticlines enable us to constrain the fault geometries using an optimized kinematic trishear model. The structure is well represented by two opposing trishear models with curved faults. Best-fit models are determined using global optimization. Finite strains are estimated by implementing strain markers (small circles) in the double trishear models. We modeled 8 parallel cross sections that are perpendicular to the strike of the structure. Each cross section is modeled independently, but some of the parameters (e.g., initial fault tips, trishear apical angles, and P/S ratio, etc.) are constrained in fixed small ranges for all cross sections in order to obtain consistent geometries and kinematics in 3-D. The results show that the modeled horizons in the best-fit models match the interpreted horizons very well for all 8 cross sections. 3-D fault surfaces and modeled horizons are generated by interpolating the best-fit models of all 8 cross sections. The 3-D model constrains the starting tip position and slip on both faults, and reveals that both faults show relatively high slips at the two ends of the structure and low slips in the middle. Shortening strains produced by thrust faulting are from 20% to 40%, concentrated on the areas adjacent to the two faults and ahead of the final fault tips. These high strain zones may correspond to degraded reservoir performance.
References Cited Brandenburg, J.P., F.O. Alpak, J. Solum, and S. Naruk, 2011, Optimized trishear modeling of incomplete seismic data: AAPG Search and Discovery Article #90124. Web accessed January 1, 2014. http://www.searchanddiscovery.com/abstracts/html/2011/annual/abstracts/brandenburg.html Camerlo, R.H., and E.F. Benson, 2006, Geometric and seismic interpretation of the Perdido fold belt; northwestern deep-water Gulf of Mexico: AAPG Bulletin, v. 90/3, p. 363-386. McClay, K., 2011, Introduction to thrust fault-related folding, in K. McClay, J. Shaw, and J. Suppe, eds., Thrust fault-related folding: AAPG Memoir 94, p. 1-19. Mount, V.S., J. Suppe, and S.C. Hook, 1990, A forward modeling strategy for balancing cross sections: AAPG Bulletin, v. 74/5, p. 521-531. Peel, F.J., C.J. Travis, and J.R. Hossack, 1995, Genetic structural provinces and salt tectonics of the Cenozoic offshore U.S. Gulf of Mexico, a preliminary analysis, in M.P.A. Jackson, D.G. Roberts, and S. Snelson, eds., Salt tectonics: a global perspective: AAPG Memoir 65, p. 153-175. Rowan, M.G., K.F. Inman, and J.C. Fiduk, 2004, Physical and temporal linkage between proximal loading and extension and distal deposition and contraction in the northwestern Gulf of Mexico basin: AAPG Annual Meeting Expanded Abstracts, v. 13, p. 120-121. Trudgill, B.D., M.G. Rowan, J.C. Fiduk, P. Weimer, P.E. Gale, B.E. Korn, R.L. Phair, W.T. Gafford, G.R. Roberts, and S.W. Dobbs, 1999, The Perdido fold belt, northwestern deep Gulf of Mexico; Part 1, Structural geometry, evolution and regional implications: AAPG Bulletin, v. 83/1, p. 88-113. Suppe, J., and D.A. Medwedeff, 1990, Geometry and kinematics of fault-propagation folding, in P. Jordan, T. Noack, S. Schmid, and D. Bernouli, eds., The Hans Laubscher volume: Eclogae Geologicae Helvetiae, v. 83/3, p. 409-454.
AAPG Annual Conference & Exhibition, 2013 Serial cross-section trishear modeling: Reconstructing 3D kinematic evolution of the Perdido fold belt Dian He Department of Geology and Geophysics, Louisiana State University, Baton Rouge JP Brandenburg Shell International Exploration and Production, Houston January 15, 2014 1
Trishear Fault-propagation folding Kink-band model Modified from Suppe & Medwedeff, 1990 January 15, 2014 2
Trishear Trishear is one type of fault-propagation folding models; it provides a quantitative description of kinematics. Allmendinger s website January 15, 2014 3
Trishear vs. kink-band models Kink-band model Trishear model trishear zone Graphical model Constant layer thickness Kink hinges Planar faults only Quantitative model (forward & inverse modeling) Variation of layer thickness Curved hinges Both planar and curved faults January 15, 2014 4
Problems in structure interpretation Fault interpretation: poorly imaged areas Trishear modeling: significantly reduce non-uniqueness Salt roller structure Alpha Wipe-out zone 500 m Conventional fault interpretation: nonunique solutions Brandenburg et al. 2011 January 15, 2014 5
Geological background A linked system: proximal extension and distal contraction. Modified from Peel et al., 1995; Rowan et al. 2004 January 15, 2014 6 Camerlo and Benson, 2006
Structural models January 15, 2014 7
An anticlinal structure to be modeled Top horizon H2 structure map Camerlo & Benson, 2006 SE 8
Conventional trishear vs. radial trishear Thick-skinned (Monoclines) Basement-involved structures Without hanging wall deformation Thin-skinned (Anticlinal folds) Deepwater toe structures With hanging wall deformation January 15, 2014 9
Curved thrust faults in deepwater passive margins Toe-thrust fold belt, Niger Delta McClay, 2011 January 15, 2014 10
Double Trishear Fully prescribed velocity field Velocity field Two opposing faults Curved fault geometry Configuration January 15, 2014 11
Workflow Trishear Input (strata data) Kinematic module Xn Objective function misfit Optimization module N iterations Best-fit parameters(x_best) Inverse modeling Initial strata (prekinematic) Forward modeling Output (best-fit model) Global optimization January 15, 2014 12
Serial cross-section modeling H2 depth structural map 8 cross sections: Parallel to one another 1 Perpendicular to the strike of the structure 2 3 4 8 7 6 5 January 15, 2014 13
Modeling results Data Models January 15, 2014 14
2D kinematics Cross section 4 Dotted lines: data Solid lines: model January 15, 2014 15
3D structure - faults Horizon H2 January 15, 2014 16
3D structure - folds Top surface: H2 January 15, 2014 17
3D kinematics Restored horizons Top surface: H1 Pre-kinematic January 15, 2014 18
Shortening Shortening by two faults Perdido fold-thrust belt map Average shortening amount: Fault F1: ~ 0.6 km Fault F2: ~ 1.3 km Total shortening in the Perdido foldthrust belt: ~ 7.5 12.5 km Proximal extension during the same period: ~ 10 km (Peel et al., 1995) January 15, 2014 19
Finite strain Heterogeneous strain High strain: nearby faults and in front of fault tips Strain map draped on horizon H2 Significance for hydrocarbon production January 15, 2014 20
Conclusions Trishear modeling provides a way to constrain the locations and geometries of faults in fault-propagation folding structures. Fault 1 does not cut through horizon H2; Fault 2 does partially. Estimated shortening in the Perdido fold-thrust belt is 7.5-12.5 km, which could balance the proximal extension (~10 km) of the same period. January 15, 2014 21
A family of solutions Final fault tips Initial fault tips January 15, 2014 22
Uncertainty Solution 1 Solution 2 Fault surfaces (model) Misfit: low Misfit: high January 15, 2014 23