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In structural geology, restoration is the process of reversing rock deformation in the subsurface through time, which can be achieved by using modeling techniques (e.g., kinematic, geometrical, and geomechanical). For instance, seismic sections from an area of interest can be used to generate restored seismic cross sections to illustrate past subsurface geology.‎<ref name=Nunns_1991>Nunns, A. G. (1991). Structural restoration of seismic and geologic sections in extensional regimes. AAPG Bulletin, 75(2), 278-297.</ref>

In structural geology, restoration is the process of reversing rock deformation in the subsurface through time, which can be achieved by using modeling techniques (e.g., kinematic, geometrical, and geomechanical). For instance, seismic sections from an area of interest can be used to generate restored seismic cross sections to illustrate past subsurface geology.‎<ref>Nunns, A. G., 1991, Structural restoration of seismic and geologic sections in extensional regimes: AAPG Bulletin, v. 75, no. 2, p. 278-297.</ref>

==Background==

==Background==

Structural restoration is a collective term that encompasses several methods used to reverse the history of deformation and yield a pre-deformational state of the area in a single step restoration or in several intermediate stages (sequential restoration).‎<ref name=Vidalroyoetal_2015>Vidal-Royo, O., T. E. Hearon IV, C. D. Connors, S. Bland, F. Schaefer, O. Ferrer, I. Mora, et al., 2015, Introduction to special section: Balancing, restoration, and palinspastic reconstruction: Intrepretation, v. 3 no. 4, p. 1N-Y1</ref> Structural restoration is linked to structural balancing, which is the adjustment of geological interpretation – of a section or an area – so that mass conservation before and after the strain is maintained. Therefore, a balanced section should be:

Structural restoration is a collective term that encompasses several methods used to reverse the history of deformation and yield a pre-deformational state of the area in a single step restoration or in several intermediate stages (sequential restoration).‎<ref>Vidal-Royo, O., T. E. Hearon IV, C. D. Connors, S. Bland, F. Schaefer, O. Ferrer, I. Mora, et al., 2015, Introduction to special section: Balancing, restoration, and palinspastic reconstruction: Intrepretation, v. 3 no. 4, p. 1N-Y1</ref> Structural restoration is linked to structural balancing, which is the adjustment of geological interpretation – of a section or an area – so that mass conservation before and after the strain is maintained. Therefore, a balanced section should be:

# accurate,  

# accurate,  

# geologically admissible,

# geologically admissible,

# restorable (it should be possible to return the section to a pre-deformation geometry),

# restorable (it should be possible to return the section to a pre-deformation geometry),

# balanced/valid (mass conservation is maintained).‎<ref name=Dahlstrom_1969>Dahlstrom, C. D. A., 1969, Balanced cross sections: Canadian Journal of Earth Sciences, v. 6, no. 4, p. 743-757.</ref><ref name=Elliott_1983>‎Elliott, D., 1983, The construction of balanced cross-sections: Journal of Structural Geology, v. 5, no. 2, p. 101.</ref>  

# balanced/valid (mass conservation is maintained).‎<ref name=Dahlstrom>Dahlstrom, C. D. A., 1969, Balanced cross sections: Canadian Journal of Earth Sciences, v. 6, no. 4, p. 743-757.</ref><ref name=Elliott>‎Elliott, D., 1983, The construction of balanced cross-sections: Journal of Structural Geology, v. 5, no. 2, p. 101.</ref>  

Therefore, structural balancing represents a powerful tool to predict unseen, subsurface geometries based on input data (e.g., outcrop geometries, well-imaged seismic sections/volumes, etc.)

Therefore, structural balancing represents a powerful tool to predict unseen, subsurface geometries based on input data (e.g., outcrop geometries, well-imaged seismic sections/volumes, etc.)

==History==

==History==

Structural balancing was first applied (but not introduced as a term) by Chamberlin‎<ref name=Chamberlin_1910>Chamberlin, R. T., 1910, The Appalachian folds of central Pennsylvania: The Journal of Geology, v. 18, no. 3, p. 228-251.</ref> to predict the geometry of the subsurface based on outcrop relationships. At the start of the Twentieth Century, deciphering the evolution of mountain belts and orogens represented an early stage of studying the kinematics associated with deformation.‎<ref name=Peach_1907>Peach, B. N., J. Horne, W. Gunn, C. T. Clough, and L. W. Hinxman, 1907, The geological structure of the North-West Highlands of Scotland: Glasgow, Scotland, HM Stationery Office, 668 p.</ref> As a defined term, balancing initially referred to the conservation of bed lengths and thicknesses.‎<ref name=Dahlstrom_1969 />

Structural balancing was first applied (but not introduced as a term) by Chamberlin‎<ref name=Chamberlin_1910>Chamberlin, R. T., 1910, The Appalachian folds of central Pennsylvania: The Journal of Geology, v. 18, no. 3, p. 228-251.</ref> to predict the geometry of the subsurface based on outcrop relationships. At the start of the twentieth century, deciphering the evolution of mountain belts and orogens represented an early stage of studying the kinematics associated with deformation.‎<ref name=Peach>Peach, B. N., J. Horne, W. Gunn, C. T. Clough, and L. W. Hinxman, 1907, The geological structure of the North-West Highlands of Scotland: Glasgow, Scotland, HM Stationery Office, 668 p.</ref> As a defined term, balancing initially referred to the conservation of bed lengths and thicknesses.‎<ref name=Dahlstrom />

In the 1960s, Bally et al.<ref name=Ballyetal_1966>Bally, A. W., P. L. Gordy, and G. A. Stewart, 1966, Structure, seismic data, and orogenic evolution of southern Canadian Rocky Mountains: Bulletin of Canadian Petroleum Geology, v. 14, no, 3, p. 337-381.</ref>‎ and Dahlstrom<ref name=Dahlstrom_1969 /> first used restoration as a tool to assess interpretation and predict geometry of structures whose interpretations were highly uncertain.‎ Advancements in computer science at the end of the century has had great impact in converting balancing and restoration concepts into software applications that can handle structural analysis of 2-D sections and maps. Most recently as computer power increased and algorithms enhanced, commercial software applications allowed for the handling of 3-D volumes balancing and restoration.

In the 1960s, Bally et al.<ref>Bally, A. W., P. L. Gordy, and G. A. Stewart, 1966, Structure, seismic data, and orogenic evolution of southern Canadian Rocky Mountains: Bulletin of Canadian Petroleum Geology, v. 14, no, 3, p. 337-381.</ref>‎ and Dahlstrom<ref name=Dahlstrom /> first used restoration as a tool to assess interpretation and predict geometry of structures whose interpretations were highly uncertain.‎ Advancements in computer science at the end of the century has had great impact in converting balancing and restoration concepts into software applications that can handle structural analysis of 2-D sections and maps. Most recently as computer power increased and algorithms enhanced, commercial software applications allowed for the handling of 3-D volumes balancing and restoration.

==Rationale and theory==

==Rationale and theory==

Understanding the underlying geology of sedimentary basins is often hindered by the existence of complex structures and/or lack of data, leading to highly uncertain models, and thus exploration/operational difficulties. For that, subsurface dynamic structural models are critical for constructing an understanding of the structural evolution of a basin of interest. For instance, tectonic controls such as faults and subsidence/uplift play a significant role in altering the subsurface geology, impacting petroleum system elements such as reservoir distribution and source rock burial depth. Dynamic restoration models as such can aid the understanding of petroleum systems processes, including hydrocarbon maturation, expulsion, migration and accumulation, and potentially present-day location of hydrocarbon fields.‎<ref name=Neumaier_2016>Neumaier, M. (2016). Structural Restoration and Basin and Petroleum Systems Modeling: Case Studies from the Monagas Fold and Thrust Belt, Venezuela and the Moroccan Atlantic Margin (Doctoral dissertation, Universitätsbibliothek der RWTH Aachen).</ref> Structural balancing and restoration combined make a good tool that can be used to validate structural models and predict untapped locations with more confidence in a geologically plausible manner.

Understanding the underlying geology of sedimentary basins is often hindered by the existence of complex structures and/or lack of data, leading to highly uncertain models, and thus exploration/operational difficulties. For that, subsurface dynamic structural models are critical for constructing an understanding of the structural evolution of a basin of interest. For instance, tectonic controls such as faults and subsidence/uplift play a significant role in altering the subsurface geology, impacting petroleum system elements such as reservoir distribution and source rock burial depth. Dynamic restoration models as such can aid the understanding of petroleum systems processes, including hydrocarbon maturation, expulsion, migration and accumulation, and potentially present-day location of hydrocarbon fields.‎<ref name=Neumaier_2016>Neumaier, M., 2016, Structural restoration and basin and petroleum systems modeling: Case studies from the Monagas Fold and Thrust Belt, Venezuela and the Moroccan Atlantic Margin: Doctoral dissertation, Universitätsbibliothek der RWTH Aachen.</ref> Structural balancing and restoration combined make a good tool that can be used to validate structural models and predict untapped locations with more confidence in a geologically plausible manner.

[[file:AlHawajAlQahtaniFigure1.jpg|center|framed|{{figure number|1}}3D restoration conducted on a faulted and folded layer (Sub-Andean Zone, Bolivia), showing a) the deformed state and b) the restored state. c) Distribution of maximum principal stress that resulted from the deformation in a.‎<ref name=Morettietal_2006>Moretti, I., F. Lepage, and M. Guiton, 2006, KINE3D: A new 3D restoration method based on a mixed approach linking geometry and geomechanics: Oil & Gas Science and Technology, v. 61. no. 2, p. 277-289.</ref>]]

[[file:AlHawajAlQahtaniFigure1.jpg|center|framed|{{figure number|1}}3-D restoration conducted on a faulted and folded layer (Sub-Andean Zone, Bolivia), showing a) the deformed state and b) the restored state. c) Distribution of maximum principal stress that resulted from the deformation in a.‎<ref name=Morettietal_2006>Moretti, I., F. Lepage, and M. Guiton, 2006, KINE3D: A new 3D restoration method based on a mixed approach linking geometry and geomechanics: Oil & Gas Science and Technology, v. 61. no. 2, p. 277-289.</ref>]]

Structural restoration can be conducted in 2-D and 3D models. As 3-D applications help to quantify spatial distribution of deformation, 2D balancing and restoration can be used to validate interpretation at parts of the volume of interest, which can be edited before committing to the 3-D workflow ([[:file:AlHawajAlQahtaniFigure1.jpg|Figure 1]]).  

Structural restoration can be conducted in 2-D and 3D models. As 3-D applications help to quantify spatial distribution of deformation, 2D balancing and restoration can be used to validate interpretation at parts of the volume of interest, which can be edited before committing to the 3-D workflow ([[:file:AlHawajAlQahtaniFigure1.jpg|Figure 1]]).