Geophysical Field Computer System
Authors: Herbert C.B. , Corbin D.G. , Hughes R.W. 
Published: October 2008

Esso Production Research Company has developed and tested a Field Computer System for application in seismic data gathering. This system will provide the field geophysicist with a much needed tool for rapid data analysis in remote areas. In addition, the Field Computer System will provide a field data format that is inherently more reliable than existing formats and that effects economies in subsequent data processing. This system is suitable for either marine or land use. It is compact and field worthy and is suitable for integration with existing seismic amplifier systems.

Introduction

The Esso Field Computer System is a geophysical tool designed to simplify seismic data handling and reduce costs, primarily on offshore seismic surveys. More specifically, it was developed to eliminate the highly encoded multiplex data format that is currently used on recording tapes in digital field recording systems. The FCS was also designed to provide an improved vertical stack capability over existing field summing units for building up energy from non-dynamite sources commonly used in marine work. Furthermore, it furnishes the field geophysicist with a much needed tool for rapid, on-site data analysis and quality control. The FCS may be used as a land or marine system and is easily installed and removed.

The current multiplex tape formats are highly encoded to preserve all of the amplifier gain information and to furnish unique synchronization characters for the beginning of each multiplex scan. The FCS eliminates the need for gain encoding by converting the data into an integer data sample. In addition, the synchronization character is no longer required since each trace is written as single physical record on the magnetic tape.

Vertical stacking of seismic data is frequently employed with low-energy marine sources such as gas or air guns and land sources such as vibrators or gas exploders. The FCS is capable of real time, true amplitude, vertical stacking of multiple input records into one output record.

One of the main objections to vertical stacking in a true amplitude manner is that an excessively noisy record may overshadow the summed data from previous records. To prevent this, a trace edit feature is included in the vertical stack program of the FCS. The Trace Edit program examines each incoming trace that is to be added to the current sum. If a trace is determined to be excessively noisy, then it is rejected and is not included in the final sum.

The FCS can also be used for "quick-look," on-site data processing. The suite of processing programs includes, but is not necessarily limited to the following functions:Gathering and display of selected tracesGathering and display of selected recordsNMO and static correctionsCDP stackingFilteringSection display

In addition to the suite of processing programs, programs such as a complete amplifier system analysis, surveying programs, and other special-purpose routines are feasible. The design of the data processing software is based on a minimum hardware configuration with minimum operator ability.