# Simple velocity tie (to wells)

Creating velocity volumes is easy in Insight - just take a look at some of our** ***suggested workflows*.

Matching a velocity to tie the well location can be more troublesome. A simple velocity tie can be achieved by calculating the vertical interval velocity in time (V0) from any "isotropic interval velocity model" in time, possibly from depth migration or velocity picking, and an interval delta model in time.

The workflow can also be used for any velocity model, including an anisotropic velocity model. The "tie velocity to wells" flow is the essence of anisotropic velocity model building. But, for well-tie, it can be applied to any given velocity model. The delta model simply acts as a scaling function. The resulting velocity and delta could not be used for imaging, but simply to reasonably tie to well.

Insight packages this workflow up into easy-to-use processes available in the *Explorationist* and *Image Gather Processing* modules.

The workflow can be split into 3 stages:

- Use the
*Synthetics*tool to create delta curves for each well that you want to influence the model. - Create an interval delta model in time.
- Calculate V
_{0}from delta and isotropic depth mig velocities.

## 1. Generate delta curves for the wells

Generate delta curves for the wells using the Synthetics tool. The delta curves will then be used to build 3D delta models (see *Delta Model*). For detailed steps to do this, refer to *Displaying the Delta Curve*.

The **Delta** tab on the **Synthetics **window will be removed soon. In the future, please use the new *Anisotropy*** **tool.

## 2. Create an interval delta model in time

The Delta Model process builds a delta model from well curves. It requires a windowing model (see *Creating a Windowing Model*) and at least one well with a delta curve.

Window model layers are automatically divided by ghost horizons using the conformability specified in the windowing model. Delta values are selected for the model at the intersection between each well and the ghost layer. These values are combined according to the specified per-layer settings.

**Note:** Create the Window model in Time as the Delta model process creates an interval delta model in time.

- In the
**Control Panel**, open the**Process**tab. - At the tab header, click the
**blue "+" icon**and select**New Process**. - Double-click
**Delta Model**. - Type a name for the process and click
**OK.**

- Select the windowing model to be used in the process at Layer horizons - select a windowing model (see
*Creating a Windowing Model*). - In the
**Output Extents**section, select a survey to be used in the delta modeling process at**Survey**. - Type the range of Inline extent, Crossline extent and time (TWT) extent for the delta model and the respective sample intervals.
- In the
**Wells**section, click the**Add Row (blue "+") icon**to add the wells used in the delta modeling.**Note:**Specific vertical extents can be specified at each well by selecting Specify well curve vertical extents (ms) option. - Select the delta curve for each well to be used in the delta modeling.
- In the Per-Layer Settings section, select the calculation type used to distribute delta in each layer in the windowing model. Available options include:
**Inverse Distance****Average of Well Values****User-specified constant**

- As a result of this process, a new delta volume is added in the Volume tab. You can further smooth the delta model using the
*Volume Smoothing*process.

## 3. Calculate V0 from delta and isotropic depth mig velocities

Calculates the vertical interval velocity in time (V_{0}) from an isotropic interval velocity model in time, and an interval delta model in time.

- In the
**Control Panel**, open the**Process**tab. - At the tab header, click the blue "+" icon and
**select New Process**. - Double-click
**V0 from delta and isotropic depth mig velocities**. - Type a name for the process and click
**OK**.

- Select the
**nmo interval velocity volume (in time)**used in delta calculation. - Select the
**delta model (time)**.- Volume is calculated using the formula
**Vo/Vnmo = 1/sqrt(1+2*delta)** - See paper Tsvankin, I., 2012, Seismic signatures and analysis of reflection data in anisotropic media: Society of Exploration Geophysicists, third edition.

- Volume is calculated using the formula
- As a result of this process, a new volume that ties the well locations is added to the
**Volume**tab. You can further smooth the delta model using the*Volume Smoothing*process.