Changes

[[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}}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>]]

Structural restoration can be conducted in 2D and 3D models. As 3D 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 3D 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]]).  

Several established techniques have been used as a basis for restoration workflow, which are:  

Several established techniques have been used as a basis for restoration workflow, which are:  

* Numerical Modeling: Numerical modeling provides a great advancement over geometric models whereby the physical properties of the formations can be modeled during the deformation. An example of such development in 2D modeling of fault-propagation folds is the trishear model that incorporates not only the strain in the hanging wall block but also that in the footwall block.‎<ref name=Erslev_1991>Erslev, E. A. (1991). Trishear fault-propagation folding. Geology, 19(6), 617-620.</ref> Three-dimensional trishear modeling followed after at the beginning of the 21st century.‎<ref name=Cristallinietal_2004>Cristallini, E. O., L. Giambiagi, and R. W. Allmendinger, 2004, True three-dimensional trishear: A kinematic model for strike-slip and oblique-slip deformation: Geological Society of America Bulletin, v. 116, no. 7-8, p. 938-952.</ref>  

* Numerical Modeling: Numerical modeling provides a great advancement over geometric models whereby the physical properties of the formations can be modeled during the deformation. An example of such development in 2D modeling of fault-propagation folds is the trishear model that incorporates not only the strain in the hanging wall block but also that in the footwall block.‎<ref name=Erslev_1991>Erslev, E. A. (1991). Trishear fault-propagation folding. Geology, 19(6), 617-620.</ref> Three-dimensional trishear modeling followed after at the beginning of the 21st century.‎<ref name=Cristallinietal_2004>Cristallini, E. O., L. Giambiagi, and R. W. Allmendinger, 2004, True three-dimensional trishear: A kinematic model for strike-slip and oblique-slip deformation: Geological Society of America Bulletin, v. 116, no. 7-8, p. 938-952.</ref>  

* Geomechanical Modeling: Geomechanical modeling covers not only the geometric aspects but also the states of stress and strain that caused and accompanied the deformation by using, boundary, discrete and finite element modeling.‎<ref name=Masinietal_2011>Masini, M., S. Bigi, J., Poblet, M. Bulnes, R. Di Cuia, and D. Casabianca, 2011, Kinematic evolution and strain simulation, based on cross-section restoration, of the Maiella Mountain: An analogue for oil fields in the Apennines (Italy), ''in'' J. Poblet and R. J. Lisle, eds., Kinematic evolution and structural styles of fold-and-thrust belts: Geological Society (London) Special Publication 349, p. 25-44.</ref>

* Geomechanical Modeling: Geomechanical modeling covers not only the geometric aspects but also the states of stress and strain that caused and accompanied the deformation by using, boundary, discrete and finite element modeling.‎<ref name=Masinietal_2011>Masini, M., S. Bigi, J., Poblet, M. Bulnes, R. Di Cuia, and D. Casabianca, 2011, Kinematic evolution and strain simulation, based on cross-section restoration, of the Maiella Mountain: An analogue for oil fields in the Apennines (Italy), ''in'' J. Poblet and R. J. Lisle, eds., Kinematic evolution and structural styles of fold-and-thrust belts: Geological Society (London) Special Publication 349, p. 25-44.</ref>

==Workflow==

==Workflow==

# restoration of eroded sections.  

# restoration of eroded sections.  

The validity of structural restoration is determined by achieving a dynamic restoration model that is both balanced and geologically plausible. It is worth pointing out that several dynamic restoration models may be considered valid. For that, it is recommended to test multiple restoration scenarios. Output results include paleotopography maps, quantified analysis of basin extension/compression, and stress/strain mapping and simulation. If the results are not valid, then seismic reinterpretation must be performed to regenerate an alternative structural/geological model. [[:file:AlHawajAlQahtaniFigure2.jpg|Figure 2]] summarizes the proposed restoration steps.

The validity of structural restoration is determined by achieving a dynamic restoration model that is both balanced and geologically plausible. It is worth pointing out that several dynamic restoration models may be considered valid. For that, it is recommended to test multiple restoration scenarios. Output results include paleotopography maps, quantified analysis of basin extension/compression, and stress/strain mapping and simulation. If the results are not valid, then seismic reinterpretation must be performed to regenerate an alternative structural/geological model. [[:file:AlHawajAlQahtaniFigure2.jpg|Figure 2]] summarizes the proposed restoration steps.

==Restoration results==

==Restoration results==

A number of results useful for a range of geological assessments can emerge from structural restoration. These include validation of interpretation, prediction of unseen structures and horizons geometries, estimation of extension and shortening, quantification of uplift and erosion, and construction of paleo-topographic and paleo-bathymetric maps. Additionally, restoration can be used to simulate geomechanical properties such as the distribution of stress and strain.  

A number of results useful for a range of geological assessments can emerge from structural restoration. These include validation of interpretation, prediction of unseen structures and horizons geometries, estimation of extension and shortening, quantification of uplift and erosion, and construction of paleo-topographic and paleo-bathymetric maps. Additionally, restoration can be used to simulate geomechanical properties such as the distribution of stress and strain.  

[[file:AlHawajAlQahtaniFigure3.jpg|thumb|300px|{{figure number|3}}Examples of 2D restoration at extensional (left) and compressional (right) regimes.‎<ref name=Neumaier_2016 />]]

file:AlHawajAlQahtaniFigure3.jpg|thumb|300px|{{figure number|3}}Examples of 2-D restoration at extensional (left) and compressional (right) regimes.‎<ref name=Neumaier_2016 />

* Validation/invalidation of interpretation and prediction of unseen geometries: Structural restoration and balancing assist in evaluating the interpretation, making them powerful tools in predicting the geometries of horizons and faults that are not imaged or only poorly imaged. In doing so, the interpreted faults and horizons are checked against geologically plausible deformational models and styles to test their viability. For instance, Chamberlin<ref name=Chamberlin_1910 /> used balancing methods to predict the geometry of the subsurface based on outcrop relationships.‎

* Validation/invalidation of interpretation and prediction of unseen geometries: Structural restoration and balancing assist in evaluating the interpretation, making them powerful tools in predicting the geometries of horizons and faults that are not imaged or only poorly imaged. In doing so, the interpreted faults and horizons are checked against geologically plausible deformational models and styles to test their viability. For instance, Chamberlin<ref name=Chamberlin_1910 /> used balancing methods to predict the geometry of the subsurface based on outcrop relationships.‎

* Estimation of uplift and erosion: Rock and surface uplifts can lead to erosion and non-deposition, which would result in the removal of previously deposited sections. This means that there will be a difference between the area/volume/line length of the restored and the deformed rock. The importance of balancing and restoration is that such dissimilarity can be pinpointed in space and time to reincorporate missing section/volume back into the geological evolution.

* Estimation of uplift and erosion: Rock and surface uplifts can lead to erosion and non-deposition, which would result in the removal of previously deposited sections. This means that there will be a difference between the area/volume/line length of the restored and the deformed rock. The importance of balancing and restoration is that such dissimilarity can be pinpointed in space and time to reincorporate missing section/volume back into the geological evolution.

* Paleotopography/paleobathymetry: Restoration, in particular 3D restoration, can be used to generate paleo-surfaces that are geologically plausible given the data. These paleo-surfaces can be incorporated into basin- and prospect-scale modeling of, for example, GDEs. Such application is important where sediment pathways are greatly affected by evolving structures. Paleo-surfaces are also important for constraining and calibrating petroleum system models over the basin scale as they can be used as an input in basin modeling.

* Paleotopography/paleobathymetry: Restoration, in particular 3D restoration, can be used to generate paleo-surfaces that are geologically plausible given the data. These paleo-surfaces can be incorporated into basin- and prospect-scale modeling of, for example, GDEs. Such application is important where sediment pathways are greatly affected by evolving structures. Paleo-surfaces are also important for constraining and calibrating petroleum system models over the basin scale as they can be used as an input in basin modeling.

==Example from industry==

==Example from industry==

The impact of structural restoration on petroleum exploration and development resides in its ability to evaluate the relative timing of petroleum system elements and processes. In particular, structural restoration constrains the timing of these elements, which helps to de-risk them when evaluating a prospect. Of particular importance is the timing of the trap formation that can be evaluated using structural restoration and compared to the timing of the hydrocarbon expulsion and migration. For example, [[:file:AlHawajAlQahtaniFigure4.jpg|Figure 4]] shows 2D geological evolution at the Monagas Fold and Thrust Belt in Venezuela, demonstrating the temporal relationship between trap formation and source rock maturation and hydrocarbon expulsion, migration, and accumulation in a structurally complex basin.‎<ref name=Neumaier_2016 />  

The impact of structural restoration on petroleum exploration and development resides in its ability to evaluate the relative timing of petroleum system elements and processes. In particular, structural restoration constrains the timing of these elements, which helps to de-risk them when evaluating a prospect. Of particular importance is the timing of the trap formation that can be evaluated using structural restoration and compared to the timing of the hydrocarbon expulsion and migration. For example, [[:file:AlHawajAlQahtaniFigure4.jpg|Figure 4]] shows 2D geological evolution at the Monagas Fold and Thrust Belt in Venezuela, demonstrating the temporal relationship between trap formation and source rock maturation and hydrocarbon expulsion, migration, and accumulation in a structurally complex basin.‎<ref name=Neumaier_2016 />  

==Challenges==

==Challenges==

One of the main challenges encountered during restoration is the three-dimensional nature of geology, which means that out-of-plane deformation may not be captured by the conventional 2D section restoration. This is most obvious when trying to restore salt basins or blocks affected by strike-slip deformation.

One of the main challenges encountered during restoration is the three-dimensional nature of geology, which means that out-of-plane deformation may not be captured by the conventional 2D section restoration. This is most obvious when trying to restore salt basins or blocks affected by strike-slip deformation.

* Salt tectonics: The underlying cause for the complexity in deformation in salt basins is that salt rock can flow in different directions that are not necessarily perpendicular to the basin margin when subjected to burial, compaction and margin tilt ([[:file:AlHawajAlQahtaniFigure5.jpg|Figure 5]]).‎<ref name=Fossen_2016>Fossen, H. (2016). Structural geology. Cambridge university press.</ref> When such flow is out-of-plane with respect to a cross section, performing 2D balancing would most likely not yield conserved cross-sectional areas of the salt and, therefore, restoration may not be adequate. This necessitates the use of 3D restoration to better restore deformation in salt basins in the regional scale and validate the results of the 2D restoration.‎<ref name=Rowanandratliff_2012>Rowan, M. G., & Ratliff, R. A. (2012). Cross-section restoration of salt-related deformation: Best practices and potential pitfalls. Journal of Structural Geology, 41, 24-37.</ref>

* Salt tectonics: The underlying cause for the complexity in deformation in salt basins is that salt rock can flow in different directions that are not necessarily perpendicular to the basin margin when subjected to burial, compaction and margin tilt ([[:file:AlHawajAlQahtaniFigure5.jpg|Figure 5]]).‎<ref name=Fossen_2016>Fossen, H. (2016). Structural geology. Cambridge university press.</ref> When such flow is out-of-plane with respect to a cross section, performing 2D balancing would most likely not yield conserved cross-sectional areas of the salt and, therefore, restoration may not be adequate. This necessitates the use of 3D restoration to better restore deformation in salt basins in the regional scale and validate the results of the 2D restoration.‎<ref name=Rowanandratliff_2012>Rowan, M. G., & Ratliff, R. A. (2012). Cross-section restoration of salt-related deformation: Best practices and potential pitfalls. Journal of Structural Geology, 41, 24-37.</ref>