Quality control of seismic surveys

Geograf offers a complete in-house software quality control (QC) tool package, supporting the exploration workflow and data life cycle. With access to the full range of QC tools from navigation, through seismic processing to interpretation, its objective is to deliver a high-fidelity data set to the client for subsequent analysis and interpretation. Wherever possible, this includes involvement in the overall quality control processes, from start to finish. Its integrated and objective QC of seismic and navigation means faster identification of problem data and a faster fix, in the right place.

Navigation and seismic data QC is closely integrated with Geograf’s navigation and seismic data processing services. Several of our experts can operate both fields, thus reducing costs and generating optimum synergies between QC and data processing. The company has also introduced navigation as a variable in seismic processing, maximising data potential.

For ultimate efficiency, Geograf uses a fully web-based IT infrastructure, with applications and remote data availability adding flexibility to the data processing flows. The ASP+D solution through Landmark provides access to software, scaleable hardware platforms and a multitude of data via the internet, bringing the office to the customer.

However, Geograf 's intention is not to provide bulk processing services of large data surveys. It plays more of an advisory role, supporting exploration staff and asset teams in specialist processing tasks during evaluation of legacy surveys when preparing basis surveys in conjunction with future 4D prospects, etc.

Seismic data as a variable in navigation processing

Historically, when seismic surveys were reprocessed, the navigation data was left out and used in its original processed version. However, in the last few years there has been more emphasis on ensuring the quality of the navigation data. This is obviously strongly related to the increased use of 4D seismic. It is believed that the navigation data should be quality controlled in conjunction with every reprocessing project.

In the event that quality control of a navigation data set should indicate that there is potential to improve the quality, the solution can sometimes be very complex. The ultimate QC of the reprocessed navigation data is to monitor, in real time, the effects they have on the seismic data.

Case Study

One client wished to carry out a traditional navigation QC of a North Sea 3D survey from the 1980’s, prior to the re-processing of seismic data. The survey consists of approximately 230 sequences and covers 6000 CMP km. Acquisition configuration was one source and dual streamers, with a shot point interval of 26.67m.

Original source/receiver navigation data was stored on UKOOA P1/90 format and raw navigation data was stored on WISLON format, which is a Western Geophysical WISDOM proprietary raw navigation format. The navigation data consisted of five Syledis ranges + 3 Hyperfix ranges to vessel, three Syledis sing-around ranges to tailbuoys, SSTS (source streamer tracking system) observations to source and streamer, and 11 streamer compasses on each streamer.

WISLON data was converted to UKOOA P2/91 format as the first step in navigation QC. Navigation QC was carried out on a selection of lines, approximately 10 percent, using ResProg, an AS GEOGRAF proprietary navigation QC system. Navigation QC indicated possible errors of 15-20m in position, mainly in inline direction.

In order to verify or invalidate a positioning error was navigation data for 16 lines selected to be re-processed – 50 percent of the lines had been acquired in direction 105? and the other 50 percent had been acquired in direction 285?. Raw navigation data had to be conditioned, i.e. editing, filtering and pre-processing, before actual processing. Syledis sing-around tailbuoy observations included considerable pre-processing in particular. The navigation processing was carried out using a Kalman filter approach.

Finally two source/receiver data sets were available: the original UKOOA P1/90 source/receiver and the new re-processed UKOOA P1/90 source/receiver. The methodology was as follows:

• Select a sub volume where the problem is evident
  Stack the sub volume using existing navigation data
• Selection of new parameters for complete reprocessing of the navigation data within the sub volume.
  The new data set will be applied to the seismic and the sub volume will be stacked again to verify the results of the new navigation data set.
• In some instances, where the problem is complex, another iteration of navigation processing might be necessary.

Geograf considered the project as a success if one of the following two conclusions can be made:

• We can demonstrate a method where the footprint in the seismic data, due to navigation errors, can be removed.
• We can conclude that the problems in the data set are not related to the navigation data.

Results
The client asked for AS Geograf’s services in regards to QC of a navigation dataset from the North Sea. The results from this QC showed a great potential for improving the quality of the data. The methodology listed above was applied to a selection of seismic lines around a swath boundary. The seismic data was processed up to and including stack, using a fairly basic processing sequence (see below).

The navigation data for this subset were reprocessed based on the findings in the QC of the data and a new stack volume was produced using the new navigation dataset.
The results from this pilot study are presented in figure1 and figure 2. The improvements are very noticeable. The continuity of the reflectors is greatly improved.

Based on the comparison of the two processed cubes, a full navigation re-processing was recommended.

Navigation processing

WISLON data was converted to UKOOA P2/91 format as the first step in navigation QC.
Navigation QC was carried out using ResProg, an AS Geograf proprietary navigation QC system. Navigation QC indicated possible errors of 15-20m, mainly in inline direction.

Seismic processing sequence

• Reformat
• Resample from 2 to 4ms
• Navigation merge (original/new)
• Trace edits
• Designature
• Spherical divergence compensation
• Deconvolution
• NMO
• Mute
• Stack

The enhanced ResProg quality control method

The Geograf proprietary ResProg software package is among the leading and most user-friendly tools for navigation QC, data processing and GIS analysis.
ResProg is available for purchase or lease on a daily rate basis.

Traditional QC method

• 1-3 hours processing time
• One person per shift (two persons total)

The enhanced ResProg method

• 10 minute processing time

Red, yellow or green?
The purpose of the traffic light system is to determine the quality level more easily. Geograf performs an additional data quality analysis onshore and this provides sufficient information to decide whether data collection should continue or not.

Effective cost reduction
ResProg effectively cuts processing time and use of personnel resources while maintaining flawless information quality.