Whats New!
l Marine Gravity Services - July 16, 2002
l Western and Central Gulf of Mexico Non-Exclusive Interpretation
l Virtual Network Adjustment (VNAtm)
l "You Should Know"...Gulf of Mexico Gravity and Magnetic Surveys
l Aeromagnetic Surveys
EDCON has had a number of questions regarding comparison of our existing data-base with more recent surveys. Based upon the number of inquiries, we thought the following information would be of general interest.
With the exception of 3 surveys acquired in Garden Banks on an HGS 3-D seismic survey, all of EDCON's gravity data in the Gulf of Mexico were acquired on "stand-alone", gravity/magnetic surveys. The reason that stand-alone gravity surveys have always been of higher quality than those acquired on seismic surveys (issues of survey priorities and equipment maintenance aside) is the Eötvös correction. The Eötvös correction is much more active and variable on a seismic survey because the seismic vessel is towing a streamer and the helmsman must actively maneuver to stay on line. GPS enables us to better define the Eötvös correction so that data now acquired on seismic vessels using SAGE meters and GPS can match the quality of the gravity-only surveys that EDCON acquired as much as 15 or 20 years ago. Our clients have recently compared EDCON survey data to data acquired using the Bell Geosystems marine gravity/gravity-gradiometer system. We have been told repeatedly that our data is better than we have claimed. We have claimed an average precision of 0.4 mGal at wavelengths of 2 km; comparison with the Bell data suggests that the EDCON data collected in Green Canyon and Mississippi Canyon are better than we have claimed, and we believe that all our data are nearly equal in quality.
EDCON's data in the Gulf of Mexico have set the standard for quality. It remains to be seen whether data acquired on routine seismic operations will match the quality of the EDCON stand-alone work. Except for definite applications where shallow anomaly resolution is needed, it also remains to be proven that the added resolution of the Bell Gradiometer system will add significant interpretation benefit to deep exploration targets over what is now available in the EDCON grid.
Salient Points:
- 1. All of EDCON's surveys were acquired as "gravity/magnetic". That is, they were not piggy-backed on a seismic survey so we had complete control over all acquisition conditions. If data were not of optimum quality for equipment, weather, or other problems, they could be re-acquired or postponed until conditions improved. This is generally not the case when the gravity is "along for the ride" on a seismic survey. It is rare that a seismic operation will be interrupted for the gravity. The magnetic data included with these surveys are of the highest quality achievable on marine surveys because of the absense of magnetic noise from seismic hardware.
- 2. A SAGE meter and GPS navigation were used on the Alaminos Canyon Survey which gives doubled assurance of high quality. EDCON's earlier surveys were run with older equipment, but high quality was achieved because of the gravity-only surveying advantages. For all other areas, the navigation system coupled with the gravity-only operation makes these data exceed the quality of any data that may be acquired in the future.
- 3. In the infill areas, the line spacing is 1-mile by 5-mile whereas the TGS Phase 45 deepwater survey will be a 2-mile by 2-mile grid. In these areas, EDCON's grid node coverage is four times that of TGS's Phase 45 deepwater survey. Furthermore, in Alaminos Canyon where the water is very deep, a line extracted from our grid at a 45° angle will have excellent resolution considering that the water depths are from 5,000' to 10,000' and that the structures are probably a minimum of 2,000' below the water bottom. We have prepared profiles to demonstrate this, and would be pleased to show them on request.
- 4. Our data are available immediately and they are integrated with the rest of the EDCON gravity data base in the Gulf.
- 5. We offer these data at prices competitive with new surveys even though they are of higher quality.
- 6. EDCON's new bathymetric compilation and Bouguer correction derived from this new model, are available to companies that own the EDCON gravity data.
In short, the EDCON data are as accurate, if not more so, than any planned large-scale surveys. Spatial resolution is better, the price is comparable and EDCON's data are available immediately. These are all compelling reasons to purchase the EDCON data.
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We now offer instrument installation, acquisition, in-field processing, final processing and interpretation of aeromagnetic surveys in Mexico, Central and South America through our associate Jaime Ruiz Reyes who is based in Mexico City. In addition, he can provide quality control and in-field processing for surveys being conducted by other contractors. Jaime has extensive experience with Picodas aeromagnetic and radiometric instrumentation. He can provide local sources for aircraft and has been involved in surveys in the area. Data processing is done using Geosoft software and color plotters for final products.
- Equipment Installation
- Acquisition
- Quality Control
- In-field Processing
- Multi-Lingual crew
- Picodas Equipment
Details regarding our services will gladly be provided on request. For more information contact: Alan Herring.