Seismic Crew Noise: A Zero Time-sharing Option
Authors: Hargreaves N. , Manin M. , Gratacos B. , Micklewright I. , Perkins C. 
Published: October 2008

When several seismic crews are active in an area it is common for each crew to acquire data only within an agreed time-period, in order to avoid generating shot-noise that might interfere with the other crews. Unfortunately, timesharing of this sort can considerably increase the cost of 3D seismic operations, and can also lead to significant delays in survey completion.

In this paper we present results from a simple alternative approach that can do away with the need for time-sharing. We propose to use location and shooting information from each seismic vessel to predict the arrival time of theinterference noise in the seismic records. Once the arrival time is known, a variety of standard data processing techniques - window edit, FK filtering, pattern removal can be used to automatically locate and remove the noise.

We will show examples of this approach for noise contaminated data from the Southern North Sea and from the West Shetlands. The examples contain interference noisewith very different characteristics, due to the different waterdepth in each area. Nonetheless, our approach is capable ofsuccessfully removing the noise in either of these cases. Furthermore, the noise elimination occurs without any significant loss of signal, a problem which can arise if random noise attenuation techniques are used to attack thistype of noise.

We propose that the co-operation that currently exists between crews working in a common geographical area should be extended to include an exchange of vessel coordinates and shooting times between the crews; in other words, we are proposing sharing co-ordinates rather thansharing time. With this information we believe that it is possible to obtain a close to zero time-sharing solution to the problem of seismic interference noise.

Introduction

When several seismic vessels are active in the same geographical area they each produce shot-generatedinterference noise (crew noise) that can contaminate the records of the other crews. At the point when noise levels are considered to be unacceptable the standard approach is to shut-down all the crews except for one, and then share acquisition time-slots around the different crews.

Although this is a very simple and normally very safe approach (providing the noise threshold at which timesharing commences is set correctly) it has the disadvantage that it can considerably increase acquisition costs and increase the total time to survey completion. Whilst the increased duration of the survey can be factored into theoverall exploration timetable (the schedule for rig placement, etc.), it is also possible that the longer acquisition period can increase the risk of unplanned downtime due to bad weather or equipment failures.

There has been an increase in the intensity of exploration in some areas in recent years, with a consequent increase in the need for time-sharing. This has been the case, forexample, in the West Shetlands area of the UK, and there has been an increased concern amongst operators in that area about the costs and delays associated with time-sharing.