User guide of paleo-structure restoration

module

1 Quick look

1.1 Introduction

Based on kinematic principles, all tectonic movements involved in the structural model could

be restored with full consideration of the tectonic evolution history. The processes and results

of the restoration can provide first-hand materials for studying the region's tectonic evolution,

and reference materials for studying the region's hydrocarbon migration history, which is

significant for the exploration and development of oil and gas.

Restore multi-directional and multi-stage complex structures.

Quantitatively describe tectonic activity intensity.

Demonstrate the tectonic evolution process with 3D models.

Construct balanced cross-sections of any orientation.

Fig.1- 1 The same layer model in different stage.

1.2 Module relationships

The system can directly use the model established in the structural modeling module. The

resulting model can be opened and edited structural modeling module.

1.3 Workflow

The process of paleo-structure restoration is the process of using the tools, such as Erosion

restoration, Inclined shear, Flexural slip, Unfolding and Flattening beds to restore

different structures.

The steps are as follows:

1) Create an appropriate tool;

2) Set parameters used by the tool;

3) Implement the tool and obtain the result;

4) Export the result.

Fig.1- 2 Workflow.

1.4 Theory

1.4.1 Principles and conditions of algorithm

Principles and conditions of using paleo-structure restoration module are as follows:

1) Rock volume is conserved during deformation.

2) Rock volume is only altered by erosion and sediment compaction.

3) Dominant deformation mode is brittle faulting.

4) Folding is related to faulting.

5) Volume losses attributed to pressure solution and tectonic compaction are assumed to be

minim.

1.4.2 Tool theory

There are four tools in the process of paleo-structure restoration, Erosion restoration,

Inclined shear, Flexural slip, Unfolding and Flattening beds. The theory would be

introduced in follows.

1) Inclined shear

The Inclined shear algorithm is effective for restoring normal faults.

A gap or void between the fault plane and the hanging-wall block is created by the extension.

The hanging-wall then collapses onto the fault plane. The collapse is controlled by the shear

vector, which is the specific path hanging-wall elements taken during the collapse. Thus

Inclined shear assumes deformation only occurs within the hanging-wall. The volume of the

hanging-wall is conserved during the restoration.

Fig.1- 3 Schematic diagram.

2) Flexural slip

The Flexural slip algorithm is used to restore the thrust fault.

It is assumed that deformation is restricted to the hanging-wall. Volume and area of the

hanging-wall beds are preserved, while footwall beds remain undeformed and are not

translated during the restoration.

Fig.1- 4 Schematic diagram.

3) Unfolding

The Unfolding tool is mainly used to restore upright folds formed by compression.

A pin plane and a folded range should be defined to determine the fold and its range to be

restored. A template plane should also be defined, which will be restored to horizontal state.

The area of the template plane and the volume of the model keep constant during the

restoration.

Fig.1- 5 Schematic diagram.

4) Flattening beds

The Flattening beds tool could restore the target surface to the datum along the reverse

process of the sedimentation, and could also restore the volume altered by sediment

compaction. The datum position, movement direction of the target surface, the initial porosity

and compacting factor of each horizon should be set before restoration. The area of the target

surface's projection is conversed during the restoration.

Fig.1- 6 Schematic diagram.

2 How to use the paleo-structure restoration tool

Please refer to the teaching video of paleo-structure restoration.

3 Special topic

3.1 Parameters introduction

1) Inclined Shear

Shear upper surface: is the target horizon, and corresponds to the" upper horizon" in fault

editing of Structure Modeling.

Generally, the Shear upper surface is set up according to the default, because the recovery

process always starts from the top of the model.

Shear lower surface: is the lower horizon affected by the fault, and corresponds to the" lower

horizon" in fault editing of Structure Modeling.

"NO" is the default option of software, which means the fault affected all horizon of the

model.

Shear vector:

Azimuth：it is the angle between shear vector and the north direction

Inclination：it is the angle between shear vector and the Z axis.

Fig.3- 1 (a)Azimuth, (b) Inclination.

By setting the Azimuth and Inclination parameters, guide he moving direction of the fault in

the process of structure restoration. Generally, we can use the default Azimuth and

Inclination parameters which can be obtained by calculated automatically according to the

position of fault in the model to calculate the model. You can modify the parameters properly

according to the research situation of the regional fault.

Surface and main fault would fit together as closely as possible when the surface is

restored：if the target fault was truncated, you need to select this function.

Shear plane：it is the plane that perpendicular to the fault strike, and located in the middle of

the fault.

2) Flexural Slip

Target surface to slide：it's the target horizon, and corresponds to the" upper horizon" in fault

editing of Structure Modeling.

Basement：it's the sliding datum in the process of restoration (As follows).

Fig.3- 2 Basement.

Movement hanging-wall: the hanging-wall would be moved, and the footwall has no

deformation during the restoration process.

Basement constraint: the deformation of the hanging-wall is constrained by the basement

form during the restoration process.

Movement direction of hanging-wall: it is the tendency of the fault.

Detachment fault group: it's the gather of all the fault in the hanging wall of the thrust fault.

Selecting the "Calculate slip fault" in the tree window, and then the Properties would be

increased an option of "Detachment fault group1" ,so we can choose the group according to

requirements.

3) Unfolding

Template plane：it is the target horizon default option is the top surface of the model in the

software.

Scoping in horizontal direction：It is a rectangular box in the model, and shows the scoping

of the fold control. We can adjust it by modifying the Forward and Reverse.

Fig.3- 3 The scoping of the fold control.

4) Flattening beds

Template plane：it is the target horizon.

Horizontal plane Z value：it is the datum position, which default value is 0.

De-compaction parameters：we need to set the initial porosity and compacting factor. There

are two ways to set, and default value is 0.

3.2 Denudation Restoration

3.2.1 Theory

"Reconstructing the strata denuded thickness" is the converse process of Denudation. Using a

series of methods to restore denuded thickness, structure form of purpose layer can be

restored to the form of no denudation.

Fig.3- 4 Schematic diagram.

3.2.2 Method

In view of the structure situation and the original data, we usually adopt the following two

methods：

Restore manually , using the method of stratum tendency extension

Restore automatically, according to the denudation amount data

Note: denudation thickness data is provided by customers, if there is no such data, denudation

thickness can be restored manually using the method of stratum tendency extension in

software.

3.2.3 Operation

1) No data of denuded thickness

By using the method of seismic interpretation, interpreting manually the data of denudation

area (method as seismic interpretation module), and adding the data to the model data ,

updating the surface, completing restore denuded thickness.

2) Provide denuded thickness data

According to the data of denudation amount, the software can automatically recover

denudation thickness. The specific steps are as follows:

In software directory select the tool: EsCalThickness; ("EsCalThickness" is a tool of

Reconstructing the strata denuded thickness)

In the opening software window, select respectively Formation scatter file, Denudation

thickness and Results file path, and then click the Calculate button to generate the resulting

file

Discrete points file of the target horizon would be replaced by the result file, imported the

model. Update the horizon, and complete denudation recovery.

Fig.3- 5 comparison photo in before and after restoration.

3.3 Eliminate the distortion during the restoration

1) Problem description:

Sometimes there may be a distortion that impact the restoring effect of model because of

different displacement of fault during the restoration, as follows. If you want to directly to

restoration, it may beget a wrong calculating result, so you need to modify the model, and

then continue the follow-up work.

Fig.3- 6 The irregular fault line is the distortion near the red line.

2) Process Mode:

If there is some distortion (not limited to such distortion), it need us to Create a new mode in

the "tool name" node. And then continue the next work. Distortion can be eliminated by this

method.

Note: After creating a new model, it is necessary to adjust model boundary according to data

of discrete points, to ensure the changes of shrinkage and stretching quantity.

Fig.3- 7(a) Original data and boundary, (b) The data and the boundary in the new model.