6 Velocity Modeling

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(1)SKUA® and GOCAD® User Guide. Part VI: Velocity Modeling.

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(3) Contents. Part VI: Velocity Modeling Chapter 1. Chapter 2. Introduction to Velocity Modeling ........................................................... 1-1 1.1. What Is Velocity Modeling? ........................................................................... 1-2. 1.2. Why Perform Velocity Modeling in SKUA or GOCAD ...................................... 1-3. 1.3. Typical Velocity Modeling Workflow............................................................... 1-4. Constructing 3D Models ........................................................................... 2-1 2.1. Constructing a Model3d ............................................................................... 2-2 2.1.1. Common Styles for Models ............................................................... 2-2 Regions ............................................................................................2-2 Layers ...............................................................................................2-3. 2.1.2. Procedure to Construct a Model3d ................................................... 2-3. 2.1.3. Creating a New Model3d From Surfaces............................................ 2-4. 2.1.4. Creating a New Model3D from a SKUA Model................................... 2-5. 2.1.5. Adding Surfaces to a Model3d.......................................................... 2-7. 2.1.6. Deleting Surfaces from a Model3d .................................................... 2-8. 2.1.7. Building a Model3d .......................................................................... 2-8. 2.1.8. Rebuilding a Model3d ...................................................................... 2-9. 2.1.9. Editing a Model3d............................................................................ 2-9 Making Surfaces and Regions Geologically Consistent ........................2-9 Removing Free Horizon Extremities in a Given Region .......................2-11 Removing All Free Extremities from a Horizon ...................................2-12. 2.1.10 Creating and Working with Layers in a Velocity Model ......................2-12 Creating Default Layers in a Velocity Model ......................................2-13 Creating a Layer from a Region in a Velocity Model ..........................2-13 Deleting a Layer in a Velocity Model.................................................2-14 Renaming a Layer in a Model3d .......................................................2-14. Contents. iii.

(4) 2.1.11 Working with Regions in a Model3d................................................ 2-15 Adding a Region to a Velocity Model Layer ...................................... 2-15 Moving a Region to a Different Velocity Model Layer ....................... 2-15 Deleting a Region from a Velocity Model Layer ................................ 2-16 Finding a Region Name in a Velocity Model ..................................... 2-16 Renaming a Region in a Velocity Model ........................................... 2-17 2.2. Constructing a Voxet Model ........................................................................ 2-18 2.2.1. Procedure to Construct a Voxet Model ............................................ 2-18. 2.2.2. Adding Surfaces to a Voxet Model Build List .................................... 2-19. 2.2.3. Removing Surfaces from a Voxet Model Build List ............................ 2-20. 2.2.4. Building a Voxet Model................................................................... 2-21. 2.2.5. Creating and Working with Layers in a Voxet Model ........................ 2-21. 2.2.6. Working with Regions in a Voxet Model .......................................... 2-22 Finding a Region Name ................................................................... 2-22 Collapsing Small Regions in a Voxet Model ...................................... 2-22. 2.2.7. Chapter 3. Creating Velocity Functions ...................................................................... 3-1 3.1. About Velocity Functions ............................................................................... 3-2. 3.2. Creating Velocity Functions from a SKUA Model ............................................. 3-4. 3.3. Visualizing Velocity Functions ........................................................................ 3-5. 3.4. Creating Velocity Functions for Time-to-Depth Conversion .............................. 3-6 3.4.1. Chapter 4. Creating and Editing Voxet Model Properties ................................... 2-22. Creating Velocity Functions from a Well Marker in Depth and a Horizon in Time ................................................................................ 3-6. 3.4.2. Creating Velocity Functions from a Time-Depth Well Log .................... 3-7. 3.4.3. Creating Velocity Functions from a Vertical Curve .............................. 3-8. Defining Property Values for Velocity Models ......................................... 4-1 4.1. Procedure to Define Velocity Model Property Values ....................................... 4-2. 4.2. Understanding the Property Model Editor ...................................................... 4-3 4.2.1. About the Property Model Editor Interface......................................... 4-3. 4.2.2. Working with the Variable Type Menu ............................................... 4-4. 4.2.3. Common Variable Definition Parameters............................................ 4-6 Variable Name.................................................................................. 4-6 Shoot Direction ................................................................................ 4-6 Shoot Position .................................................................................. 4-7 Impact Point .................................................................................... 4-8. 4.3. iv. Contents. Defining Layer Property Values Directly .......................................................... 4-9 4.3.1. Assigning Constant Values to Properties or Variables .......................... 4-9. 4.3.2. Defining Properties or Variables by Using Linear Functions.................. 4-9. 4.3.3. Defining Properties or Variables by Using Interpolation ..................... 4-10. 4.3.4. Defining Properties or Variables from Grid Properties ....................... 4-12. 4.3.5. Defining Values from Surface or Layer Boundary Properties .............. 4-13. SKUA® and GOCAD® – Paradigm™ 2011 With Epos® 4.1 Data Management.

(5) Part VI: Velocity Modeling. Defining Values from Surface Boundaries .........................................4-13 Defining Values from Layer Boundaries.............................................4-14 Notes on Defining Values from Surfaces and Layers ..........................4-18 4.4. Defining Properties or Variables by Using Property Functions..........................4-19 4.4.1. Defining Properties or Variables by Using Linear Functions ................4-20. 4.4.2. Defining Properties or Variables by Using Exponential Functions ........4-22. 4.4.3. Defining Property Functions by Using Scripts ....................................4-23 About Script Property Functions .......................................................4-23 Creating Script Property Functions ...................................................4-24. 4.5. Chapter 5. Visualizing Property Functions ......................................................................4-25 4.5.1. Painting a Voxet with a Velocity Model Property ...............................4-25. 4.5.2. Painting a Velocity Function on a Grid ..............................................4-26. 4.6. Adding Properties to Velocity Models............................................................4-27. 4.7. Deleting Properties from Velocity Models ......................................................4-28. Creating Grid Properties with Geostatistical Functions ........................... 5-1 5.1. Geostatistics System File Formats................................................................... 5-2 5.1.1. GS File ............................................................................................. 5-2 Variogram and Associated Parameters File Format ..............................5-2 GS File Examples ...............................................................................5-3. 5.2. 5.3. User Guide. 5.1.2. Column_Average_Map File ............................................................... 5-4. 5.1.3. Scattergram File ............................................................................... 5-4. 5.1.4. External_Histogram File .................................................................... 5-5. 5.1.5. Facies_Map File ................................................................................ 5-5. 5.1.6. Annealing_Schedule File ................................................................... 5-5. Estimating Grid Properties with Kriging Algorithms ........................................ 5-6 5.2.1. Estimating Properties with Kriging .................................................... 5-6. 5.2.2. Estimating Properties with Kriging with Trend .................................... 5-8. 5.2.3. Estimating Properties with Kriging with External Drift .......................5-10. 5.2.4. Estimating Properties with Bayesian Kriging......................................5-12. 5.2.5. Estimating Properties with Collocated Cokriging ...............................5-14. 5.2.6. Estimating Properties with Indicator Kriging .....................................5-16. Running Geostatistical Simulations ...............................................................5-18 5.3.1. Running Sequential Gaussian Simulations (SGS) ................................5-18. 5.3.2. Running Non-Conditional Sequential Gaussian Simulations ...............5-21. 5.3.3. Running Collocated Cokriging Simulations .......................................5-22. 5.3.4. Running Sequential Indicator Simulations (SIS)..................................5-24. 5.3.5. Running Annealing Simulations .......................................................5-26. 5.3.6. Running Cloud Transform Simulations with P-Fields ..........................5-29. 5.3.7. Performing Categorical Histogram Corrections .................................5-31. 5.3.8. Performing Continuous Histogram Corrections .................................5-32. 5.3.9. Filling Grids with Facies Map Data....................................................5-34. Contents. v.

(6) Chapter 6. Chapter 7. Chapter 8. vi. Contents. Performing Velocity Conversions ............................................................. 6-1 6.1. Converting the Velocity Type in One Domain .................................................. 6-2. 6.2. Converting the Velocity Type in Different Domains.......................................... 6-3. 6.3. Converting the Velocity Type of Velocity Functions.......................................... 6-5. Interpolating Velocity ............................................................................... 7-1 7.1. Smoothing a Voxet Property .......................................................................... 7-2. 7.2. Interpolating Velocity Linearly Between Surfaces............................................. 7-3. 7.3. Extracting the Velocity Trend From a Voxet ..................................................... 7-4. 7.4. Extracting the Velocity Trend From a Well Property ......................................... 7-5. Performing Time and Depth Domain Conversions................................... 8-1 8.1. Converting Objects Using a Velocity Cube ...................................................... 8-2. 8.2. Converting a Seismic Cube ............................................................................ 8-4. 8.3. Reassigning an Object to the Correct Domain ................................................ 8-7. 8.4. Converting Seismic Lines ............................................................................... 8-8. 8.5. Converting a SKUA Model........................................................................... 8-10. 8.6. Rescaling Objects in the Same Domain ......................................................... 8-12 8.6.1. Rescaling Objects in Same Domain .................................................. 8-12. 8.6.2. Rescaling a Seismic Cube in Same Domain....................................... 8-13. SKUA® and GOCAD® – Paradigm™ 2011 With Epos® 4.1 Data Management.

(7) 1 Introduction to Velocity Modeling In this chapter. Overview. •. "What Is Velocity Modeling?," page 1-2. •. "Why Perform Velocity Modeling in SKUA or GOCAD," page 1-3. •. "Typical Velocity Modeling Workflow," page 1-4. This section introduces velocity modeling, describes the benefits of using Paradigm™ SKUA® and Paradigm™ GOCAD® to perform velocity modeling, and describes a typical velocity modeling workflow.. 1-1.

(8) 1.1. What Is Velocity Modeling? The main source of imaging data of the subsurface for large areas is seismic. Because seismic data is a measure of the travel time of a sound wave, seismic data provides an image in time of the subsurface. But reservoir engineers, geologists, and drillers need to work in the depth domain to manipulate objects in real space. To convert the data acquired in time, the geophysicists uses a velocity model to convert from the time domain to the depth domain.The basic equation is:. V = DT Where: V = velocity; T = travel time provided by the seismic data; D = well depth. You create the velocity model from the seismic velocity and well data (checkshot, calibrated integrated sonic logs). After you build the velocity model, you can perform the time-to-depth conversion. Velocity modeling is an important step in seismic imaging, especially for complex reservoirs. The greater the complexity of the geological structure, the greater the need for an accurate velocity model at high resolution. SKUA provide the structural model that helps you achieve such a velocity model.. 1-2. Introduction to Velocity Modeling. SKUA® and GOCAD® – Paradigm™ 2011 With Epos® 4.1 Data Management.

(9) Part VI: Velocity Modeling. 1.2. Why Perform Velocity Modeling in SKUA or GOCAD SKUA or GOCAD, through the SKUA Structure and Stratigraphy, Velocity Modeling, and Time-Depth Conversion modules, enables you to create basic to advanced velocity models and then to perform time-to-depth conversions. For information, see:. • • • • • Creating a velocity model based on the SKUA model. When you build the SKUA model, SKUA automatically creates a sealed 3D model. You can use this SKUA model to create a velocity model. A sealed 3D model has the following advantages:. • • • • Creating velocity model using velocity functions Using geostatistics to update the velocity model. "Creating a velocity model based on the SKUA model," page 1-3 "Creating velocity model using velocity functions," page 1-3 "Using geostatistics to update the velocity model," page 1-3 "Converting velocity," page 1-3 "Performing time-to-depth conversion," page 1-3. Layers are automatically generated. Supports unlimited structural complexity. Faults are taken into account. Ability to define any velocity values using mathematical continuous functions.. SKUA and GOCAD support the Velocity Functions object type. You can use Velocity Functions to create a basic velocity model from sparse data where the velocity is interpolated throughout the entire area of interest. Defining the velocity model is iterative. SKUA and GOCAD provides geostatistic tools that help you create and refine the velocity model.. Converting velocity. SKUA and GOCAD provide tools for you to convert velocity from one type to another in same domain or to a different domain. For example, converting RMS velocity to average velocity.. Performing time-todepth conversion. After you finish refining the velocity mode, you can convert your data (seismic cube, interpretation data, for example) from time to depth using simple vertical stretching. If you want to perform migration, you can use Paradigm™ GeoDepth®.. User Guide. 1.2 Why Perform Velocity Modeling in SKUA or GOCAD. 1-3.

(10) 1.3. Typical Velocity Modeling Workflow This section describes a typical velocity modeling workflow. Depending on your goals, you can use a different workflow. SKUA and GOCAD support a variety of workflows. Step. Description. 1. Import the data needed to perform the time-to-depth conversion:. Import data. • Seismic data • Well data • Interpretation data (faults, horizons, salt bodies) If this data is in the Epos repository, you can import this data from SeisEarth into a SKUA project. For more information about importing, see:. • Part II: Data Import and Export, Chapter 1, "Importing Data." • Part I: Getting Started, Chapter 4, "Sharing Data with Paradigm Applications." 2. Quality check the data. 3. Build seismic velocity model. After you import the data, verify the data is correct and consistent. SKUA and GOCAD provide several methods for creating the velocity model:. • Create a basic velocity model using velocity functions. For more information, see "About Velocity Functions" on page 3-2.. • Create a basic to complex velocity model using a 3D model. For more information, see "Creating Velocity Functions from a SKUA Model" on page 3-4. In GOCAD, you need to build the 3D model, and then define a property for the velocity model. For more information, see Part VIII: 3D Grid Building, Chapter 6, "Building a 3D Reservoir Grid in GOCAD," and Chapter 4, "Defining Property Values for Velocity Models." • Create a basic to complex velocity model using a grid and geostatistics. In this approach, you create a geologic grid using the structural data. With geologic grids, you can keep the structural unit information, which is appropriate when working in a layer-cake model. Using the Property Modeling workflow, you can populate the grid using checkshot data as hard data (after you convert the RMS velocity into interval velocity) and then interpolate the interval velocity throughout the grid using geostatistics (like simple kriging).. 1-4. 4. Calibrate seismic velocity to well data. You can force the velocity model to fit the well markers when you perform a domain conversion.. 5. Interpolate velocity (optional). For more information, see Chapter 7, "Interpolating Velocity.". 6. Perform time-todepth conversion. For more information, see Chapter 8, "Converting Objects Using a Velocity Cube.". Introduction to Velocity Modeling. SKUA® and GOCAD® – Paradigm™ 2011 With Epos® 4.1 Data Management.

(11) 2 Constructing 3D Models. In this chapter. Overview. •. "Constructing a Model3d," page 2-2. •. "Constructing a Voxet Model," page 2-18. There are two types of model objects in Paradigm™ SKUA® and Paradigm™ GOCAD ® : the Model3d, which is the main focus of this chapter, and the Voxet model.. 2-1.

(12) 2.1. Constructing a Model3d • • • • • • • • • •. 2.1.1. "Common Styles for Models," page 2-2 "Procedure to Construct a Model3d," page 2-3 "Creating a New Model3d From Surfaces," page 2-4 "Creating a New Model3D from a SKUA Model," page 2-5 "Adding Surfaces to a Model3d," page 2-7 "Deleting Surfaces from a Model3d," page 2-8 "Building a Model3d," page 2-8 "Editing a Model3d," page 2-9 "Creating and Working with Layers in a Velocity Model," page 2-12 "Working with Regions in a Model3d," page 2-15. Common Styles for Models There are three sets of styles common to models:. • • •. Regions Layers Fault blocks. Regions In a model object, a region is a closed space bounded by Surfaces and/or the edges (boundaries) of the model.. Figure 2–1 Model region area. Individual regions. If there are any regions in the model, their names appear in the Regions area. You can adjust the styles associated with each region.. 2-2. •. Visible. Turns the display of all selected regions on and off.. •. Region check boxes. When the Visible check box is selected, turns the display of individual regions on and off.. •. Region color. Changes the display color of an individual region.. Constructing 3D Models. SKUA® and GOCAD® – Paradigm™ 2011 With Epos® 4.1 Data Management.

(13) Part VI: Velocity Modeling. Voxet models are visualized through their parent voxets. (Select the voxet model in the Objects browser, but display the voxet itself in the 3D Viewer.). Layers A layer is composed of one or more geologically related regions (for example, a layer of sand faulted into two separate bodies). For information on creating and working with layers, see "Creating and Working with Layers in a Velocity Model" on page 2-12. By default, a layer is named after its top bounding surface.This is to follow the geologic convention of naming a surface Top of Something. For example, the name "Top of Miocene" implies that the layer below the Top of Miocene surface is the Miocene layer.. Figure 2–2 Model layer area. Tip If you think that there are layers in your model but they do not appear in the Layers area, there may be leaks in your model (a layer needs to be completely bounded by Surfaces and/or model boundaries).. If there are any layers in the model, their names appear in the lower half of the Layers area. You can adjust the styles associated with each layer.. •. Visible. Turns the display of all selected layers on and off.. •. Layer check boxes. When the Visible check box is selected, turns the display of individual layers on and off.. •. Layer color. Changes the display color of an individual layer.. Voxet Models are visualized through their parent voxets. (Select the Voxet Model in the Objects browser, but display the voxet itself in the 3D Viewer.). 2.1.2. Procedure to Construct a Model3d Table 2–1 outlines the basic functions to facilitate constructing 3D models and modifying them after construction.. Table 2–1 Basic functions for creating and modifying 3D models. User Guide. To do this. See this procedure. Create a Model3d from one or more Surfaces. "Creating a New Model3d From Surfaces" on page 2-4. Create a Model3d from a SKUA model. "Creating a New Model3D from a SKUA Model" on page 2-5. Add Surfaces to the Model3d you created 1. "Adding Surfaces to a Model3d" on page 2-7. Delete or detach Surfaces from the Model3d you created 1. "Deleting Surfaces from a Model3d" on page 2-8. Force an update of the Model3d based on any surface additions, deletions, or detachments 2. "Building a Model3d" on page 2-8. Recreate the Model3d from its input Surfaces 3. "Rebuilding a Model3d" on page 2-9. 2.1 Constructing a Model3d. 2-3.

(14) 1. You can choose whether to incorporate the Build function into your changes, prompting the program to recompute and update the model immediately. If you forego an automatic build to save computation time, changes will not take effect until you run the Build function as a separate step. 2. The Build function does not take into account any changes to the input Surfaces themselves. 3. The Rebuild function is most useful when there have been changes to the input Surfaces, and you want to re-cut them.. 2.1.3. Creating a New Model3d From Surfaces When you create a new Model from a set of Surfaces, each surface intersects each face of the model, and surfaces may also intersect each other, or "self-intersect" (so that the program can detect regions enclosed by surfaces). This operation can take some time to carry out.. Figure 2–3 Model3d examples. Regular model. To create a new Model3d from a set of Surfaces. 2-4. Model with intersecting surfaces. 1. Select Surface commands > Model3d > From Surfaces to open the Create Model3d From Surfaces dialog box.. 2. In the Name box, type the name of the new model.. 3. In the Surfaces box, enter one or more surfaces to use in building the model.. Constructing 3D Models. SKUA® and GOCAD® – Paradigm™ 2011 With Epos® 4.1 Data Management.

(15) Part VI: Velocity Modeling. 4. If you want to indicate that the surfaces are self-intersecting, select the Self intersection check box. If you clear this check box, the program will compute only the area between each surface and the voxet itself. Note Typically, surfaces are not self-intersecting.. 5. If you want the program to define the Model3d borders consistently, select the Define borders check box.. 6. If you want the program to update the model immediately when you click OK or Apply, select the Build check box. Note If you select this check box, the cut operations will be run on all surfaces.. 7. 2.1.4. Click OK or Apply.. Creating a New Model3D from a SKUA Model Use this command to create a Model3d from SKUA horizons, faults, and boundaries.. To create a Model3d from a SKUA model. About merging small throws. User Guide. 1. Select Surface commands > Model3d > From SKUA Model to open the CreateModel3d from SKUA Model Horizons, Faults and Boundaries dialog box.. 2. In the SKUA Model box, enter the SKUA model to use to create the Model3d.. 3. In the Model3d name box, type the name of the Model3d to create.. 4. If you want to merge fault and horizon contacts that have a small throw, expand the Advanced area, select the Merge small throw check box, and then in the Max throw box, type a threshold value. When the throw is below the specified threshold, the fault and horizon contacts will be merged. For more information about this option, see "About merging small throws" on page 2-5.. 5. Click OK or Apply.. Areas with a very small throw can often cause failures in the construction of the model3D. If you merge the fault throw, the contacts will be collocated in these areas, which simplifies the construction of the Model3D. For an illustration, see Figure 2–4.. 2.1 Constructing a Model3d. 2-5.

(16) Figure 2–4 Merging small throws. Do not merge contacts. Merge contacts. 2-6. Constructing 3D Models. SKUA® and GOCAD® – Paradigm™ 2011 With Epos® 4.1 Data Management.

(17) Part VI: Velocity Modeling. 2.1.5. Adding Surfaces to a Model3d Use this function to add new surfaces to a model after it is created.. To add surfaces to a Model3d. 1. Select Surface commands > Model3d > Add Surface to open the Add Surfaces in Model3d dialog box.. 2. In the Model3d box, enter one or more existing models to which the surfaces will be added.. 3. In the Surfaces box, enter one or more surfaces to be added to the model.. 4. If you want to create copies of the added surfaces before modifying their topology (cutting them) to construct the model, select the To copy check box. Note Each copied surface is named according to the convention model name_surface name . For example, if you add a surface H1 to a model m1, the new surface will be called m1_H1.. User Guide. 5. If you want the program to update the model immediately when you click OK or Apply, select the Build check box.. 6. If you want the program to define the Model3d borders consistently, select the Define borders check box.. 7. Click OK or Apply.. 2.1 Constructing a Model3d. 2-7.

(18) 2.1.6. Deleting Surfaces from a Model3d Use this function to delete surfaces from a model after it is created.. To delete surfaces from a Model3d. 2.1.7. 1. Select Surface > Model3d > Kill Surface to open the Kill Surfaces in Model3d dialog box.. 2. In the Model3d box, enter one or more existing models from which the surfaces will be deleted.. 3. In the Surface surfaces box, enter one or more surfaces to be deleted from the model.. 4. If you want the program to update the model immediately when you click OK or Apply, select the Build check box.. 5. If you want the program to define the Model3d borders consistently, select the Define borders check box.. 6. Click OK or Apply.. Building a Model3d When you run a "build," the program analyzes the types of changes that occurred to the model, such as adding or deleting surfaces, and performs the operations necessary to recompute the model regions. (If only surfaces were deleted, no intersection phase is necessary, and the build should be relatively fast.). To build a Model3d. 2-8. 1. Select Surface commands > Model3d > Build to open the Build 3D-Model dialog box.. 2. In the Model3d box, enter one or more models to build.. Constructing 3D Models. SKUA® and GOCAD® – Paradigm™ 2011 With Epos® 4.1 Data Management.

(19) Part VI: Velocity Modeling. 2.1.8. 3. If the surfaces in the model are already pre-cut and you want the program to construct the model without finding the intersection between all the surfaces, clear the With cut check box.. 4. If you want the program to define the Model3d borders consistently, select the Define borders check box.. 5. Click OK to carry out the command and close the dialog box, or click Apply to carry out the command and keep the dialog box open.. Rebuilding a Model3d Using this command, you can recreate a model (see "Creating a New Model3d From Surfaces" on page 2-4), including re-cutting all the input surfaces. The "rebuild" function actually modifies the input data on which the model is built. In contrast, the regular "build" function updates the model only, based on added or deleted input data.. To rebuild a Model3d. 2.1.9. 1. Select Surface commands > Model3d > Rebuild to open the Rebuild 3D-Model dialog box.. 2. In the Model3d box, enter one or more models to rebuild.. 3. If you want the program to define the Model3d borders consistently, select the Define borders check box.. 4. Click OK or Apply.. Editing a Model3d For information, see:. • • •. "Making Surfaces and Regions Geologically Consistent," page 2-9 "Removing Free Horizon Extremities in a Given Region," page 2-11 "Removing All Free Extremities from a Horizon," page 2-12. Making Surfaces and Regions Geologically Consistent You can use a model to detect geologic inconsistency between geologic surfaces. This function does the following:. User Guide. •. Removes pieces of surfaces which are not geologically correct. •. Removes parts of top surfaces that are inside intrusive regions. 2.1 Constructing a Model3d. 2-9.

(20) •. Removes parts of top surfaces that are above their erosion surfaces (the erosion surface is younger than the horizon, but part of the horizon is above the erosion surface). •. Automatically rebuilds the model regions. As shown in the left image of Figure 2–5, two horizons of older age than the salt body penetrate the salt volume, splitting the salt region into three regions. The right image displays the results of the "Make surfaces and regions geologically consistent" function. The non-geologic parts have been removed, creating a hole inside the two horizons and a unique region. Important In order for the algorithm to work properly, you need to first set geologic information on all of the different surfaces (see Part IV: Foundation Modeling, "Defining and Working with Geologic Features" on page 8-1). In Figure 2–5, the salt surface was declared an intrusive surface with an age younger than the two top surfaces.. Figure 2–5 Making figures geologically consistent. Before. To make a Model3d geologically consistent. After. 1. Select Surface commands > Model3d > More > Make Geological Consistency to open the Make Surfaces and Regions Geologically consistent dialog box.. 2. In the Model3d box, enter one or more models to make geologically consistent.. 3. Click OK or Apply. Note You need to run the "build" function separately to rebuild the model itself. (See "Building a Model3d" on page 2-8.). 2-10. Constructing 3D Models. SKUA® and GOCAD® – Paradigm™ 2011 With Epos® 4.1 Data Management.

(21) Part VI: Velocity Modeling. Removing Free Horizon Extremities in a Given Region Use this function to automatically remove free radial edges from all horizon surfaces within one given region of a model. This function can be especially useful for removing free extremities extending outside of the model in the Universe region (see Figure 2–6 for an example).. Figure 2–6 Removing free horizon extremities in a region. Before removing free extremities. To remove free horizon extremities in a given region. User Guide. After removing free extremities. 1. Select Surface commands > Model3d > More > Remove Free Extremities to open the Remove Free Horizon Extremities in a given region from Model3d dialog box.. 2. In the Model3d box, enter one or more models.. 3. In the Region box, enter the name of the region in which horizon extremities will be removed.. 4. Click OK or Apply.. 2.1 Constructing a Model3d. 2-11.

(22) Removing All Free Extremities from a Horizon Use this function to automatically remove free radial edges, or extremities, from one horizon surface throughout all regions of a model. This function can be especially useful when the model has been constructed from surfaces in which borders have been extended to ensure intersections between faults and horizons.. Figure 2–7 Removing free extremities from a horizon. Before removing free extremities. To remove all free extremities from a horizon. 2.1.10. After removing free extremities. 1. Select Surface commands > Model3d > More > Remove Horizon Free Extremities to open the Remove Free Horizon Extremities from Model3d dialog box.. 2. In the Model3d box, enter one or more models.. 3. In the AtomsSet horizon box, enter the name of the horizon surface from which extremities will be removed.. 4. Click OK or Apply.. Creating and Working with Layers in a Velocity Model The first three functions described in this section are valid for both Model3ds and Voxet Models.. • • • •. 2-12. Constructing 3D Models. "Creating Default Layers in a Velocity Model," page 2-13 "Creating a Layer from a Region in a Velocity Model," page 2-13 "Deleting a Layer in a Velocity Model," page 2-14 "Renaming a Layer in a Model3d," page 2-14. SKUA® and GOCAD® – Paradigm™ 2011 With Epos® 4.1 Data Management.

(23) Part VI: Velocity Modeling. Creating Default Layers in a Velocity Model You can automatically compute a default set of layers for a velocity model. This function groups regions into layers by using geologic information attached to the surfaces bounding the regions. To ensure that this function works properly, be sure to set geologic information for fault and boundary surfaces (see Part IV: Foundation Modeling, "Defining and Working with Geologic Features" on page 8-1). If no geologic information is set, all surfaces are assumed to be top surfaces, and the stratigraphic time is computed from the lowest z value of the surface; this can lead to errors in layer computation.. To create a default layer set. 1. Select Surface, Voxet, or SGrid commands > Model3d or Model (as applicable) > Create Defaults to open the Create Default LayerSet inside Model dialog box.. 2. In the Model box, enter one or more models in which the layer set will be created. Important The model should contain regions.. 3. Click OK or Apply.. Creating a Layer from a Region in a Velocity Model Use this function to create a layer from a specific region in a velocity model.. To create a layer from a region. User Guide. 1. Select Surface, Voxet, or SGrid commands > Model3d or Model (as applicable) > Create One to open the Create new Layer inside Model from an existing Region dialog box.. 2. In the Model box, enter one or more models to which the layer will be added.. 3. In the Layer name box, type the name of the new layer.. 4. In the Region box, enter the name of the region from which the layer will be created.. 5. Click OK or Apply.. 2.1 Constructing a Model3d. 2-13.

(24) Deleting a Layer in a Velocity Model Use this function to delete a layer from a velocity model.. To delete a layer from a velocity model. 1. Select Surface, Voxet, or SGrid commands > Model3d or Model (as applicable) > Remove Layer to open the Remove Layer dialog box.. 2. In the Model box, enter one or more models from which the layer will be deleted.. 3. In the Layer box, enter the layer to be deleted.. 4. Click OK or Apply.. Renaming a Layer in a Model3d Use this function to rename a layer in a Model3d.. To change a layer name in a velocity model. 2-14. 1. Select Surface commands > Model3d > Rename to open the Change Model Layer name dialog box.. 2. In the Model box, enter one or more models containing the layer to be renamed.. 3. In the Layer box, enter the layer to be renamed.. 4. In the New name box, type the new name of the layer.. 5. Click OK or Apply.. Constructing 3D Models. SKUA® and GOCAD® – Paradigm™ 2011 With Epos® 4.1 Data Management.

(25) Part VI: Velocity Modeling. 2.1.11. Working with Regions in a Model3d Most of the functions described in this section are valid for both Model3ds and Voxet Models. The model is rebuilt automatically after each of these functions.. • • • • •. "Adding a Region to a Velocity Model Layer," page 2-15 "Moving a Region to a Different Velocity Model Layer," page 2-15 "Deleting a Region from a Velocity Model Layer," page 2-16 "Finding a Region Name in a Velocity Model," page 2-16 "Renaming a Region in a Velocity Model," page 2-16. Adding a Region to a Velocity Model Layer Use this function to add a region to a layer within a velocity model.. To add a region to a velocity model layer. 1. To open the Add Region to Layer dialog box, select either:. •. Surface commands > Model3d > Region > Add to Layer.. •. Voxet or SGrid commands > Model > Add to Layer.. 2. In the Model box, enter one or more models.. 3. In the Region box, enter the region to be added to the layer.. 4. In the Layer box, enter the destination layer.. 5. Click OK or Apply.. Moving a Region to a Different Velocity Model Layer Use this function to move a region to a different layer within a velocity model.. To move a region to a different layer. 1. Display the model regions and layers in the 3D Viewer.. 2. Select either:. • • 3. User Guide. Surface commands > Model3d > Region > Move to Layer. Voxet or SGrid commands > Model > Move to Layer.. In the 3D Viewer, click the region to be moved, then click the destination layer.. 2.1 Constructing a Model3d. 2-15.

(26) Deleting a Region from a Velocity Model Layer Use this function to delete a region from a layer within a velocity model.. To delete a region from a layer. 1. To open the dialog box, select either:. •. Surface commands > Model3d > Region > Remove from Layer.. •. Voxet or SGrid commands > Model > Remove from Layer.. 2. In the Model box, enter one or more models.. 3. In the Region box, enter the region to be deleted from the layer.. 4. In the Layer box, enter the target layer.. 5. Click OK or Apply.. Finding a Region Name in a Velocity Model Use this function to find the name of a specific region within a velocity model.. To find the region name of a displayed region. Do one of the following:. . Select Voxet or SGrid commands > Model > Region > Find Name, and then click the region in the 3D Viewer. – or – Select Selection toolbar > Get XYZ Coordinate 3D Viewer.. , and then click the region in the. The status bar displays the region name. Region name. 2-16. Constructing 3D Models. SKUA® and GOCAD® – Paradigm™ 2011 With Epos® 4.1 Data Management.

(27) Part VI: Velocity Modeling. Renaming a Region in a Velocity Model Use this function to rename a region within a velocity model.. To rename a region. User Guide. 1. To open the Change Model Region name dialog box, select either:. •. Surface commands > Model3d > Region > Rename.. •. Voxet or SGrid commands > Model > Rename.. 2. In the Model box, enter one or more models.. 3. In the Region box, enter the region to be renamed.. 4. In the New name box, type the new name of the region.. 5. Click OK or Apply.. 2.1 Constructing a Model3d. 2-17.

(28) 2.2. Constructing a Voxet Model For information, see:. • • • • • • •. 2.2.1. "Procedure to Construct a Voxet Model," page 2-18 "Adding Surfaces to a Voxet Model Build List," page 2-19 "Removing Surfaces from a Voxet Model Build List," page 2-20 "Building a Voxet Model," page 2-21 "Creating and Working with Layers in a Voxet Model," page 2-21 "Working with Regions in a Voxet Model," page 2-22 "Creating and Editing Voxet Model Properties," page 2-22. Procedure to Construct a Voxet Model Table 2–2 outlines the basic functions to facilitate constructing Voxet Models and modifying them after construction.. Table 2–2 Basic functions for creating and modifying Voxet Models. To do this. See this procedure. Specify the surfaces to be included in the Voxet Model 1. "Adding Surfaces to a Voxet Model Build List" on page 2-19. Exclude surfaces from a Voxet Model 1. "Removing Surfaces from a Voxet Model Build List" on page 2-20. Perform the initial build of the Voxet Model or force an update based on any surface additions or deletions 2. "Building a Voxet Model" on page 2-21. 1. You can choose whether to incorporate the Build function into your changes, prompting the program to recompute and update the model immediately. If you forego an automatic build to save computation time, changes will not take effect until you run the Build function as a separate step. 2. The Build function does not take into account any changes to the input surfaces themselves.. For information, see:. • • • • About Voxet Models. "About Voxet Models," page 2-18 "Building effective Voxet Models," page 2-19 "Visualizing Voxet Models," page 2-19 "Voxet Model warnings," page 2-19. When you create a Voxet, an empty Voxet Model is created automatically as well. A Voxet Model is the gridded volume confined within the cage of the Voxet. You can cut the Voxet Model volume with Surfaces to create gridded sub-volumes. A layer is a contiguous subvolume. A Voxet Model, therefore, is a bounded volume that consists of gridded subvolumes called layers. Theoretically, a Voxet Model has at least one layer (the entire Voxet volume), but for practical purposes, a Voxet Model is considered empty until you create at least one subvolume within the model (see "Building a Voxet Model" on page 2-21). Since building a Voxet Model is simpler than building a Model3d, it can be helpful to build a Voxet Model to check the validity of layers before building a Model3d. In an effective Voxet Model, the Voxet should be smaller than all the Surfaces that will to cut the Voxet walls, creating layers.. 2-18. Constructing 3D Models. SKUA® and GOCAD® – Paradigm™ 2011 With Epos® 4.1 Data Management.

(29) Part VI: Velocity Modeling. Building effective Voxet Models. In the left Voxet in Figure 2–8, all the sub-horizontal Surfaces cut all four walls of the Voxet, and there is room above the top and below the bottom Surface. A Voxet Model built from those Surfaces and the Voxet will have six layers (and six regions in the Voxet). In the right Voxet in Figure 2–8, the Voxet is so big that it does not intersect any of the Surfaces. A Voxet Model built from those Surfaces and the Voxet will have only two layers: the layer inside the middle closed Surface and the layer outside it.. Figure 2–8 Voxet examples. Effective Voxet. Ineffective Voxet. A Voxet created from an object box (see Part IV: Foundation Modeling, "Creating a Voxet from an Objects Box" on page 6-10) is meant to include all objects selected; therefore, we do not recommend building a Voxet Model from that set of objects. To guarantee proper intersections (cutting), create the Voxet from end points (see Part IV: Foundation Modeling, "Creating a Voxet from Corner Points" on page 6-8), in which you can specify the XYZ locations of the Voxet corner points.. Visualizing Voxet Models. Voxet Model warnings. 2.2.2. Voxet Models are visualized through their parent Voxets. (Select the Voxet Model in the Style dialog box, but display the Voxet itself in the 3D Viewer.) When you successfully create a layer in a Voxet Model, a region is automatically created in the corresponding Voxet. You can also view the regions in the Voxet to visualize the Voxet Model.. •. When you build a Voxet Model, part of the process is cutting the Voxet with the Surfaces, which cuts the connectivity in the Voxet. (See Part IV: Foundation Modeling, "Cutting a Voxet with Surfaces" on page 6-12.). •. Once you have built a Voxet Model, do not add or delete a Surface and rebuild (see "Voxet Model warnings" on page 2-19).. Adding Surfaces to a Voxet Model Build List Use this function to specify the Surfaces to be included in a Voxet Model. After specifying the surfaces, you can proceed to build the Voxet Model (see "Building a Voxet Model" on page 2-21), or you can continue to modify the build list by adding or deleting other surfaces. Important Once you have built the Voxet Model, do not add or delete Surfaces and rebuild.. User Guide. 2.2 Constructing a Voxet Model. 2-19.

(30) To add surfaces to the build list of a Voxet Model. 1. Display the Voxet and the Surfaces in the 3D Viewer. In order to create valid regions in the model, the Surfaces should cut one another and/or the Voxet walls (see Figure 2–8 on page 2-19).. 2. Select Voxet commands > Model > Add Surfaces to open the Add Surfaces to Voxet Model dialog box.. 3. In the Voxet box, enter one or more voxets. Note A Voxet Model is always attached to a Voxet.. 4. The names of the displayed Surfaces will be listed automatically in the Surface surfaces box.. 5. Click OK or Apply. Note The Voxet Model will not actually be built until you execute the Build function (see "Building a Voxet Model" on page 2-21).. 2.2.3. Removing Surfaces from a Voxet Model Build List Use this function to specify Surfaces to be excluded from a Voxet Model. After specifying the surfaces, you can proceed to build the Voxet Model (see "Building a Voxet Model" on page 2-21), or you can continue to modify the build list by adding or deleting other surfaces. Important Once you have built the Voxet Model, do not add or delete Surfaces and rebuild.. To remove Surfaces from the build list of a Voxet Model. 1. Select Voxet commands > Model > Remove Surfaces to open the Remove Surfaces from Voxet Model dialog box.. 2. In the Voxet box, enter one or more voxets. Note A Voxet Model is always attached to a Voxet.. 3. 2-20. Constructing 3D Models. The names of the displayed Surfaces will be listed automatically in the Surface surfaces box.. SKUA® and GOCAD® – Paradigm™ 2011 With Epos® 4.1 Data Management.

(31) Part VI: Velocity Modeling. 4. Click OK or Apply. Note The Voxet Model will not actually be built until you execute the Build function (see "Building a Voxet Model" on page 2-21).. 2.2.4. Building a Voxet Model Use this function to build a Voxet Model. To build a Voxet Model, you need to first add Surfaces to its build list (see "Adding Surfaces to a Voxet Model Build List" on page 2-19). The Surfaces should intersect one another or the Voxet walls in order to create layers (see Figure 2–8 on page 2-19). Avoid modifying a Voxet Model once you have built it (see "Voxet Model warnings" on page 2-19). Note that Voxet Models are visualized through their parent Voxets. (Select the Voxet Model in the Style dialog box, but display the Voxet itself in the 3D Viewer.) When you successfully create a layer in a Voxet Model, a region is automatically created in the corresponding Voxet. As an option, you can also view the regions in the Voxet to visualize the Voxet Model.. To build a Voxet Model. 1. Select Voxet commands > Model > Build to open the Build Voxet Model dialog box.. 2. In the Voxet box, enter one or more voxets. Note A Voxet Model is always attached to a Voxet.. Tip Grouping regions into layers automatically can reduce the number of regions dramatically in cases where two surfaces are very close to each other.. 3. Important Layer construction relies on the presence of geologic Information for each horizon and fault (see Part IV: Foundation Modeling, Chapter 8, "Defining and Working with Geologic Features."). 4. 2.2.5. If you want to construct the layers only, select the Layers only check box. Alternatively, you can construct layers manually (see "Creating Default Layers in a Velocity Model" on page 2-13).. Click OK or Apply.. Creating and Working with Layers in a Voxet Model For information, see "Creating and Working with Layers in a Velocity Model" on page 2-12.. User Guide. 2.2 Constructing a Voxet Model. 2-21.

(32) 2.2.6. Working with Regions in a Voxet Model For information, see:. • •. "Finding a Region Name in a Velocity Model," page 2-16 "Collapsing Small Regions in a Voxet Model," page 2-22. Finding a Region Name See "Finding a Region Name in a Velocity Model" on page 2-16. Collapsing Small Regions in a Voxet Model Use this command to modify the topology of a Voxet. This command creates a hole inside the boundary of a small region, which is then absorbed into a larger region and disappears. If the small region was bounded by more than one region, there is no way to control the region into which the small region will be absorbed.. To collapse small regions. 1. Select Voxet commands > Model > Remove Small Regions to open the Filter/ Collapse Small Voxet Model Regions dialog box.. 2. In the Voxet box, enter one or more voxets. Note A Voxet Model is always attached to a Voxet.. 2.2.7. 3. In the nb cells box, enter the region threshold size. Every region smaller than the size you specify will be collapsed into neighboring regions.. 4. Click OK or Apply.. Creating and Editing Voxet Model Properties For information about other editing commands for Voxet Models, see "Editing a Model3d" on page 2-9. In addition, you can use the Property Model Editor tools with Voxet Models, Model3ds, and SKUA models, as described in Chapter 4, "Defining Property Values for Velocity Models.". 2-22. Constructing 3D Models. SKUA® and GOCAD® – Paradigm™ 2011 With Epos® 4.1 Data Management.

(33) 3 Creating Velocity Functions. In this chapter. Overview. •. "About Velocity Functions," page 3-2. •. •. "Creating Velocity Functions from a SKUA Model," page 3-4. "Visualizing Velocity Functions," page 3-5. •. "Creating Velocity Functions for Timeto-Depth Conversion," page 3-6. Paradigm™ SKUA ® and Paradigm™ GOCAD ® provide a Velocity Functions object that you can use to perform time-to-depth conversions. Depending on the data that is available on the velocity function, you can export it to the Epos repository as vertical functions or as pencils. If you generate the velocity functions from a SKUA model, the pencils carry all of the geologic model information that can be shared in Epos-enabled applications, such as Paradigm™ GeoDepth ®. The commands to create velocity functions are available with the Velocity Modeling and Time-Depth Conversion module.. 3-1.

(34) 3.1. About Velocity Functions Velocity functions are geometric objects that you can use in velocity modeling for time-todepth conversion. You can share velocity functions with Epos-enabled applications by exporting them to an Epos database as:. • •. Vertical functions. Contain only velocity properties. Pencils. Contain geologic, structural model information.. Note The vertical functions and pencil data that you import from Epos are stored as velocity functions in SKUA or GOCAD. For more information, see:. • • • What are velocity functions?. "What are velocity functions?," page 3-2 "Properties on velocity functions," page 3-2 "Velocity category," page 3-3. Velocity functions correspond to a set of vertical curves that carry a velocity property (See Figure 3–1). The geometry of the velocity functions is defined by the objects that you use to create them, which can include the following objects:. • • •. From vertical curves From vertical wells From a SKUA model. In SKUA and GOCAD, velocity functions belong to the Velocity category.. Figure 3–1 Velocity Functions object showing the average velocity property shown with seismic in 3D Viewer Velocity functions carrying the average velocity (Vavg). Properties on velocity functions. 3-2. Velocity functions contain property values at the following locations:. • •. Creating Velocity Functions. At their nodes (called properties) On their segments (called edge properties). SKUA® and GOCAD® – Paradigm™ 2011 With Epos® 4.1 Data Management.

(35) Part VI: Velocity Modeling. Velocity category. In the Objects browser, the category Velocity can contain the following object types that are used in a velocity modeling workflow:. • • •. User Guide. Velocity Functions 3D Surveys Curves. 3.1 About Velocity Functions. 3-3.

(36) 3.2. Creating Velocity Functions from a SKUA Model From a SKUA model you can create velocity functions that carry the structural information of the SKUA model (units, boundaries, dip and azimuth). You can then export the velocity functions to the Epos repository and use them in Epos-enabled applications. For example, you can use them in GeoDepth to perform tomography. For more information, see:. • • Prerequisites To create velocity functions from a SKUA model. "Prerequisites," page 3-4 "To create velocity functions from a SKUA model," page 3-4. To use this command, you need a SKUA model and a survey as input data. 1. Select Velocity commands > Velocity Functions > Create from SKUA Model to open the Compute Velocity Functions from SKUA Model dialog box.. 2. In the SKUA Model box, select the SKUA model from which you want to create the velocity functions.. 3. In the Name box, specify a name for the velocity function output.. 4. If you want to use a survey to define the areal sampling of the velocity functions, select the Use survey check box, and then in the Survey box, enter the survey. Otherwise, in the Voxet cube box, enter a voxet cube.. 5. In the Inline jump and Crossline jump boxes, type a value of 1 or greater to indicate how many samples to compute. For example, if you accept the default value of 1, all samples are used; If you enter 5, every 5th sample is used and the computed velocity function is less dense.. The command generates a velocity function with X, Y, Z built-in properties and properties computed from the SKUA model (azimuth, dip and boundaries). It also creates the units property (located under edge properties), which is a discrete property that corresponds to the stratigraphic unit of the SKUA model. The velocity function has the same domain as the SKUA model.. 3-4. Creating Velocity Functions. SKUA® and GOCAD® – Paradigm™ 2011 With Epos® 4.1 Data Management.

(37) Part VI: Velocity Modeling. 3.3. Visualizing Velocity Functions In the 3D Viewer, you can visualize velocity functions that you create from a SKUA model. For more information, see:. • • To slice a velocity function. "To slice a velocity function," page 3-5 "To change the velocity function display," page 3-5. You can use the Slicer toolbar to "slice" a velocity function in the 3D Viewer so that you can examine it. 1. In the Objects browser, select the velocity function to display it in the 3D Viewer.. 2. On the Slicer toolbar, click Slicer. to turn on the slicer.. The slicer displays the outline of a box around the velocity function displayed in the 3D Viewer. The slicer limits the view in the 3D Viewer to the volume of the slicer box. For more information about using the Slicer toolbar, see Part III: Visualization, "Slicer Toolbar" on page 3-8.. To change the velocity function display. User Guide. Using styles, you can display the velocity function by sections and by selected horizon and fault boundaries. 1. Right-click the velocity function and select Style > Editor to open the Style dialog box.. 2. From the Graphic tab, use the axis-1 and axis-2 boxes to change the velocity function section that is displayed in the 3D Viewer.. 3. To display the velocity function only within a specified horizon or fault boundary, in the Boundaries area, select the horizon or fault, and then select the Show only check box.. 3.3 Visualizing Velocity Functions. 3-5.

(38) 3.4. Creating Velocity Functions for Time-toDepth Conversion You can use velocity functions to perform a time-to-depth conversion. With velocity functions, you can perform a time-to-depth conversion of a full volume even when there is sparse data (SKUA or GOCAD interpolates when there is sparse data). Thus, you can easily generate an initial, approximate time-to-depth conversion without needing to create a complex velocity model. For more information, see:. • • •. 3.4.1. "Creating Velocity Functions from a Well Marker in Depth and a Horizon in Time," page 3-6 "Creating Velocity Functions from a Time-Depth Well Log," page 3-7 "Creating Velocity Functions from a Vertical Curve," page 3-8. Creating Velocity Functions from a Well Marker in Depth and a Horizon in Time You can create velocity functions with an average velocity computed from the input data (well marker in depth and calibrated horizon in time). It allows you to easily generate an initial velocity model to perform time-to-depth conversion. For more information, see:. • • Prerequisites To create velocity functions from depth markers and horizon in time. 3-6. "Prerequisites," page 3-6 "To create velocity functions from depth markers and horizon in time," page 3-6. To use this command, you need well markers in depth and horizons in time as input data. 1. Select Velocity commands > Velocity Functions > Create from Calibrated Markers and Horizons to open the Create Velocity Functions from well markers and time horizons dialog box.. 2. In the Name box, specify the name of the velocity functions to create.. 3. In the Wells box, select the wells in depth that contain the markers that will be matched to the time horizons.. 4. In the Object Horizons box, select the time horizons. The time horizons can be a Surface, 2D-Grid, or Horizon Grid object.. Creating Velocity Functions. SKUA® and GOCAD® – Paradigm™ 2011 With Epos® 4.1 Data Management.

(39) Part VI: Velocity Modeling. As shown in Figure 3–2, the command generates two velocity functions (one in depth domain and one in time domain). The velocity function properties are:. •. X, Y, Z built-in properties. •. Vavg. The average velocity computed from the input data.. SKUA or GOCAD computes the average velocity for the well markers and horizons that share the same feature as follows:. Vavg =  2  Depth marker    Surface time  Where:. Depth marker Surface time. = the depth value of the well marker. = the two-way seismic time. The command automatically handles unit conversion.. Figure 3–2 Velocity Function in Objects browser. Velocity functions. 3.4.2. Creating Velocity Functions from a TimeDepth Well Log You can create velocity functions from a two-way-time (TWT) well log. For more information, see:. • •. User Guide. "Prerequisites," page 3-6 "To create velocity functions from a Time-Depth well log," page 3-8. 3.4 Creating Velocity Functions for Time-to-Depth Conversion. 3-7.

(40) Prerequisites To create velocity functions from a Time-Depth well log. To use this command, you need wells in depth with a time-depth log as input data. 1. Select Velocity commands > Velocity Functions > Create from T-D Well Curves to open the Create Velocity Functions from Time/Depth Logs dialog box.. 2. In the Name box, specify a name for the velocity functions to create.. 3. In the Wells box, enter wells in the depth domain that carry a time log.. 4. In the Time/Depth Log box, select the time log.. 5. To create the velocity functions in the time domain, select the Create Velocity Functions in Time Domain check box.. The command generates a velocity functions in the domain of the well (unless you select the Create Velocity Functions in Time Domain check box). It creates a function at every well KB location and a vertical point at every curve point (point on the time-depth log). The velocity function properties are:. 3.4.3. •. X, Y, Z built-in properties. •. Vavg. The average velocity computed from the depth information of the well path and the time log.. Creating Velocity Functions from a Vertical Curve You can create velocity functions from vertical curves . For more information, see:. • •. 3-8. Creating Velocity Functions. "Prerequisites," page 3-9 "To create velocity functions from curves," page 3-9. SKUA® and GOCAD® – Paradigm™ 2011 With Epos® 4.1 Data Management.

(41) Part VI: Velocity Modeling. Prerequisites To create velocity functions from curves. To use this command, you need vertical curves with a velocity property as input data. 1. Select Velocity commands > Velocity Functions > Create from Vertical Curve to open the Create Velocity Functions from Curves dialog box.. 2. In the Curve box, select the curves on which to compute the velocity functions. Note If you select a non vertical curve, the command does not create velocity functions.. 3. In the Name box, specify a name for the velocity functions.. This command transforms the vertical curve objects into a Velocity Functions object and transfers all of the curve object properties onto the Velocity Functions object. The sampling of the curves defines the sampling of the velocity function. The created velocity functions have the domain of the curve object.. User Guide. 3.4 Creating Velocity Functions for Time-to-Depth Conversion. 3-9.

(42) 3-10. Creating Velocity Functions. SKUA® and GOCAD® – Paradigm™ 2011 With Epos® 4.1 Data Management.

(43) 4 Defining Property Values for Velocity Models In this chapter. •. "Procedure to Define Velocity Model Property Values," page 4-2. • • •. Overview. •. "Understanding the Property Model Editor," page 4-3. "Defining Properties or Variables by Using Property Functions," page 4-19. •. "Working with the Variable Type Menu," page 4-4. "Visualizing Property Functions," page 4-25. •. "Defining Layer Property Values Directly," page 4-9. "Adding Properties to Velocity Models," page 4-27. •. "Deleting Properties from Velocity Models," page 4-28. In a velocity model such as a Model3d or a Voxet model, properties cannot be attached to data points (as in geometric objects) because there is no connection between the Surfaces. Instead, you can use the Property Model Editor in Paradigm™ SKUA ® and Paradigm™ GOCAD ® to define property values (such as velocity) for each model layer through mathematical methods including constants, variables, and functions. Functions, which vary in complexity, can in turn include elements such as defined variable, the properties and xyz-positions of nearby Voxets and Surfaces, mathematical equations, and so on.. 4-1.

(44) 4.1 Table 4–1 Workflow for defining property values. 4-2. Procedure to Define Velocity Model Property Values For this step. See. 1. Create a velocity model with regions. "Constructing a Model3d" on page 2-2 "Constructing a Voxet Model" on page 2-18. 2. Create layers in the velocity model. "Creating and Working with Layers in a Velocity Model" on page 2-12. 3. Create global properties (property names) for the velocity model. "Adding Properties to Velocity Models" on page 4-27. 4. Define property values for the layers using the Property Model Editor. "Defining Layer Property Values Directly" on page 4-9 "Defining Properties or Variables by Using Property Functions" on page 4-19. Defining Property Values for Velocity Models. SKUA® and GOCAD® – Paradigm™ 2011 With Epos® 4.1 Data Management.

(45) Part VI: Velocity Modeling. 4.2. Understanding the Property Model Editor • • •. 4.2.1. "About the Property Model Editor Interface," page 4-3 "Working with the Variable Type Menu," page 4-4 "Common Variable Definition Parameters," page 4-6. About the Property Model Editor Interface The Property Model Editor is a tool for creating property values (such as velocity) for the various layers of a model. The Property Model Editor (see Figure 4–1) is composed of three main areas: the model selector, the property browser, and the value definition area. You can also use the Property Model Editor to review any existing properties or variables for the layers within the model.. Figure 4–1 Property Model Editor Model selector. Commands. Property list. Variable type. Value definition. To open the Property Model Editor. User Guide. 1. To open the dialog box, do either of these:. •. Select Surface, Voxet, or SGrid commands > Model3d or Model (as applicable) > Editor.. •. In the Objects browser, right-click any velocity model property > select Editor.. 4.2 Understanding the Property Model Editor. 4-3.

(46) 2. In the Model box, enter the velocity model for which you want to define properties.. Important Ensure that the velocity model contains, at a minimum, regions and layers. For more information, see Table 4–1 on page 4-2.. 4.2.2. Working with the Variable Type Menu You can define property values for the layers in your model by using constants, variables, and functions. Functions, which vary in complexity, can in turn include elements such as defined variables ("intermediate variables"), the properties and xyz-positions of nearby Voxets and Surfaces, mathematical equations, and so on.. Figure 4–2 Property browser Global property Layer. Variable. Tip A special layer called Everywhere facilitates creating variables that will be available in all layers, and a special Property Model called All Properties enables the creation of variables that will be available in all Property Models.. Layer-specific properties. When you create a new property, it is global, or applicable to the whole model (see Figure 4–2). Every layer in the model will contain the property, but the layer-specific values are initially undefined. You need to define properties for each layer individually, as the different layers in a model do not share property functions or variables. Since variables or functions that you define in one layer do not apply to other layers, you can duplicate the same variable and function names in different layers. Use the Add Variable, Remove Variable, and Add Property commands to:. • •. Create properties for the model, if you have not already done so (for information, see "Adding Properties to Velocity Models" on page 4-27) Create or delete variables or functions that define property values Note You can define a variable either as a separate step or "on demand," while filling out the value definition area (shown in Figure 4–1 on page 4-3).. The value definition area displays the details of the property or variable definition selected in the Variable type box. This menu of value definition types contains:. • • Table 4–2 Variable definitions. Five options to define layer property values directly (see "Defining Layer Property Values Directly" on page 4-9) Three options to define layer property values using property functions (see "Defining Properties or Variables by Using Property Functions" on page 4-19). Variable definition. For information, see. Undefined Build In Constant. "Assigning Constant Values to Properties or Variables," page 4-9. Linear Function. "Defining Properties or Variables by Using Linear Functions," page 4-20. Exponential Function. 4-4. Defining Property Values for Velocity Models. SKUA® and GOCAD® – Paradigm™ 2011 With Epos® 4.1 Data Management.

(47) Part VI: Velocity Modeling. To define a property or variable (overview). Variable definition. For information, see. Script. "Defining Property Functions by Using Scripts," page 4-23. Linear Function of Property. "Defining Properties or Variables by Using Linear Functions," page 4-9. Interpolated Property. "Defining Properties or Variables by Using Interpolation," page 4-10. From Grid Property. "Defining Properties or Variables from Grid Properties," page 4-12. From Surface or Layer Boundary Property. "Defining Values from Surface or Layer Boundary Properties," page 4-13. 1. If you need to create a new variable, do the following: Note You can define a variable either as a separate step or "on demand," while filling out the value definition area.. a. In the property browser (see Figure 4–2), click the layer to which the variable will belong.. b. Click Add Variable to open the Variable Name dialog box.. c. In the Name box, type the name of the new variable, and then Click OK.. The new variable appears in the property browser. 2. In the property browser, click the property or variable that you want to define or edit.. 3. If you are defining the property or variable for the first time, select an option in the Variable type box. (The default variable type is as Undefined.) Note Each option in the Variable type box brings up a different panel, as indicated in Figure 4–2.. User Guide. 4. Define the parameters of the selected option in the value definition area. (See "Defining Layer Property Values Directly" on page 4-9 or "Defining Properties or Variables by Using Property Functions" on page 4-19.). 5. Click Update Variable Definition to apply your changes.. 4.2 Understanding the Property Model Editor. 4-5.

(48) 4.2.3. Common Variable Definition Parameters Many property/variable definition options share the following common parameters or concepts:. • • • •. "Variable Name," page 4-6 "Shoot Direction," page 4-6 "Shoot Position," page 4-7 "Impact Point," page 4-8. Variable Name Direct property definitions. If you are defining a layer property directly using one of the options in the Variable type menu, ensure that the Variable name displayed matches the name of the layer property you are defining; otherwise, the program assumes that you are defining an intermediate variable to be used in a property function (see "Defining Properties or Variables by Using Property Functions" on page 4-19).. Intermediate variables. If you are defining an intermediate variable to be used in a property function, ensure that the Variable name displayed is different than the name of the layer property; otherwise, the program assumes that you are defining the layer property itself.. Variables in different layers. When you create (define) a variable, it is associated with a specific layer and property, outside of which it has no meaning. If you want to use the variable in any other layers, you need to recreate the variable in the other layers. Since the various layers do not share data, you can duplicate the same variable and function names in different layers.. Shoot Direction Shoot direction, which is also known as the search direction or dir_Z, specifies the direction along which to search for impact points (see "Impact Point" on page 4-8). There are four shooting directions, but not all of them are available in every menu. In the Property Model Editor, only the first three are available; in the Constraints menu (in the Surface commands), only the fourth is available.. dir_Z = +1. The command searches in the positive Z (up) direction from the shoot position (see "Shoot Position" on page 4-7), as shown in Figure 4–3 (b).. dir_Z = -1. The command searches in the negative Z (down) direction from the shoot position, as shown in Figure 4–3 (b).. two_way. The command searches in both the positive and negative Z directions from the shoot position, as shown in Figure 4–3 (a). This option overwrites the dir_Z = +1 or dir_Z = -1 options. When shooting two ways, you can only shoot from inside (see "from_inside" on page 4-7).. 4-6. Defining Property Values for Velocity Models. SKUA® and GOCAD® – Paradigm™ 2011 With Epos® 4.1 Data Management.

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