VE432 Training Course Manual

Chapter 8

VIBROSEIS SOURCE MANAGEMENT

MAIN APPLICATIONS (V8.4)

TABLE OF CONTENTS

1. INTRODUCTION 0

2. SIMULTANEOUS OPERATION 0

3. FLIP-FLOP MODE 0

3.1 PRINCIPLE 0

3.2 HCI SETUP FOR FLIP-FLOP OPERATIONS 1

4. SLIP-SWEEP 0

4.1 OVERVIEW 0

4.2 GENERAL DESCRIPTION 1

4.3 OPERATION WITH SN388 AND VE432 6

4.4 MORE ABOUT SLIP-SWEEP 15

5. HIGH-LINE NOISE 0

5.1 GENERAL 0

5.2 IMPLEMENTING HIGH-LINE NOISE ELIMINATION ON THE HCI 2

6. HARMONIC LINE ELIMINATION 0

6.1 Introduction 0

6.2 REVIEW OF PHYSICAL RELATIONSHIPS ON SINE WAVES 0

6.3 GENERAL LAW 3

6.4 EXAMPLE OF PRACTICAL IMPLEMENTATION 6

6.5 APPLYING THE PRINCIPLE 8

7. DPG MASTER SLAVE OPERATION 0

8. NAVIGATION 0

8.1 Implementation 0

8.2 One fleet or Flip-Flop navigation setup 3

8.3 Slip sweep navigation setup 4

1.Introduction

This chapter covers different methods of sweeping, serving two major purposes:

- Saving time: Flip-flop, Slip-sweep, Simultaneous or Master/Slave operation

- Getting better data: High-Line or harmonic elimination.

The description in this chapter is provided as an overview of the flexibility offered by the SN388/VE432 system. Naturally, it is for the user to make the best possible use of that flexibility to extend it to further applications.

2.Simultaneous operation

This method uses two groups of vibrators sweeping at the same time on two shotpoints but generating different sweeps. Overleaf is an example of setup for simultaneous operation.

Naturally the sweeps are assumed chosen with careful consideration for the frequencies from the two sweeps not to mix.

Group 2

Group 1

a1*a1, a2*a2

where

a1: pilot group 1

a2: pilot group 2

3.Flip-flop mode

3.1Principle

The Flip-flop mode uses two groups of vibrators sweeping alternately. This allows one group to move while the other is sweeping.

With this mode of operation the aim is to have the shortest possible time between two consecutive sweeps. To achieve this goal the SN388 should be set to Continuous operation mode and acquisitions should be started as the vibrator leader presses the Ready button on his DSD.

3.2Hci setup for flip-flop operations

As a matter of fact there are two ways of setting the Setup parameters in the OPERATION environment. The OPERATION environment allows us to use a wide range of setups illustrated in the two methods below.

The first set-up method is also the easiest:

Y ou define two process types and two acquisition types. The two process types are exactly the same but one is defined for fleet 1 (acq.1) and the other for fleet 2 (acq.2).

Then you alternate the two process types in the Operation table.

The above example of double zigzag Setup will allow flip-flop operations.

The following points are worthy of note:

- The method is very easy to set up.

- Each acquisition is independent.

- The setup, however, needs to be modified if one of the fleets has to sweep any of the shotpoints of the other.

The second method allows us to avoid the requirement mentioned above.

This time we use a common Process Type for the two fleets.

In that case you have to prepare two groups of shotpoints in the Operation Setup, for example odd shotpoints for fleet 1 and even shotpoints for fleet 2. But there is still no link between shotpoints and any fleet (unlike with method A) as a single Process type is used for both fleets and all shotpoints use the same Process Type.

The fleet is selected by selecting a shotpoint in either pane in the Operation main window: for example choosing a shotpoint in the upper pane will select fleet 1 whereas choosing one in the lower pane will select fleet 2.

Pane for fleet 2

Shot 4

Shot 1

Pane for fleet 1

The two panes allow all shotpoints to be displayed. You may select two shotpoints at a time. As a result, the spread will be prepared as the addition of the two spreads selected. When the observer activates the GO button the HCI will take the first shot, then the second. Then the data will be dumped to the tape (two files) and the spread for the next two shots will be formed.

The advantages of the second method are.

- It is very easy to have a fleet sweep a shotpoint prepared for the other fleet.

- Less time is lost between acquisitions as the spread is formed every two shots.

The only disadvantage lies in that the spread is the addition of the individual spreads for the shotpoints of the two fleets.

NOTE: The above example is for flip-flop operations but naturally it is possible operate with stacking, as in the example below.