Introduction

This document outlines the general steps in calibrating a velocity data (downhole sonic or laboratory velocity profile) using a time-depth data (such as checkshots) in order to generate a time-depth relationship (TDR) curve and be able to accurately hang/tie the well/borehole data in time domain (i.e., Core-Log-Seismic Correlation). At every depth level, the calibration process calculates the drift, which is equivalent to the checkshot time minus the integrated sonic time, and applies this value to the sonic data. The result is a sonic data that is adjusted to match the times derived from the checkshot survey, thereby combining the high data resolution of the sonic log, and the accuracy of the checkshot data.

The workflow requires that a well or borehole is created in a properly defined project, with a reflection seismic profile, a downhole sonic or core velocity and a checkshot data already imported. It is also suggested that the input data be optimized, applying mis-tie analysis on the seismic data, and conditioning (e.g., despike) on the log data.

Procedure

1. In the Seismic interpretation toolbar tab > Seismic-well calibration group > click on the Seismic well tie button (Figure 1).

Figure 1: Petrel Seismic well tie button.

2. In the Seismic well tie dialog box that appears, select Sonic calibration from the Study type dropdown list. Select the well or borehole to use (Figure 2).

Figure 2: Seismic well tie window configured for creating a new sonic calibration study.

3. For the template, select the default sonic calibration template (Figure 2).

Select the parameters in the various tabs at the lower half of the dialogue box. Contextual help or brief description of each parameter is shown if the cursor is moved over the corresponding blue button

4.  Input

In the input tab, select a delta-t or velocity data, preferably one that has been conditioned (e.g., despike) of outliers. The initial TDR can also be a velocity data (stacking, wireline, or laboratory/core) (Figure 2).

5. Output

Figure 3: Output tab for seismic well tie window.

6. Datuming

Figure 4: Datuming tab for seismic well tie window, with the different parameters that define a marine datum.

7. Time-depth

Figure 5: Time-depth tab for seismic well tie window.

8. Options

Figure 6: Options tab for the seismic well tie window.

9.  When you are satisfied with the parameters, click OK.  A well section window will appear showing the results of the calibration process.

Figure 7: Initial result of the sonic calibration displayed in a well section window.

10. Once the initial sonic calibration output is created, the knee curve can be edited so that the knees can coincide with the checkshot points or to additional locations such as defined well tops. To do this, open the Well tie editing tool palette from Seismic interpretation > Seismic-well calibration group > Well tie editing.

Figure 8: Well tie editing tool palette.

Click on the "Knees at checkshots" button (first row, second from the left button).  This will create knees at every checkshot points, as shown below:

Figure 9: Well section window for sonic calibration with knees at every checkpoint.

11. Save TDR and apply to well.

Credits

This guide is largely derived from the Petrel 2017 Geophysics training manual:

Schlumberger Limited (2018) Petrel 2017 : Petrel Geophysics Workflow/Solutions Training. Houston: Schlumberger, 764 pp.