A New Dimension in 3D

Abstract

Abstract There is an increasing number of marine 3D seismic surveys being acquired with concurrently recorded high resolution gravity and magnetics data. Instrumentation, navigation, and processing advances have led to significantly increased gravity and magnetics data resolution. State of the art workstation software tools provide a means for the integration of seismic, gravity, and magnetic data. Interpretations have aided in the delineation of complex imaging problems including the verification and enhancement of seismic velocity models. A review is given of technical developments, economic considerations, and case studies in support of integrated 3D marine surveys utilizing gravity, magnetics, and seismic data. Introduction Using new interpretation case studies from the Gulf of Mexico and offshore Europe, it is possible to gain insights into enhancing and constraining the interpretation of 3D seismic data using gravity and magnetics methods. Using digital horizons interpreted from a 3D seismic volume and high resolution gravity and magnetics data, an integrated and constrained 3D geologic model can be quickly built and tested. The acquisition of high resolution gravity and magnetic data in conjunction with 3D seismic surveys is now an accepted normal in Europe, and is quickly gaining acceptance in the Gulf of Mexico. Over 300 OCS blocks of 3D-acquired gravity and major areas of high resolution aeromagnetic data have been and are now being recorded in the Gulf of Mexico. The use of high resolution gravity in seismic velocity analysis and the use of velocity grids for localized, focused density input to gravity models is now possible. A detailed example of a localized conversion of a velocity cube to a density volume is provided from the Southern Additions, offshore Louisiana. A brief review of instrumentation, processing techniques, costs, and integrated software applications is provided to set the framework for the interpretation case studies. Gravity and magnetic instrumentation has decreased in size and increasedin sampling and resolution power. Processing of the data using high quality DGPS positioning data has resulted in a dramatic increase in the resolution of shipbome gravity. Workstation applications are now in use which facilitate the direct transfer of data and models between seismic and gravity/ magnetic modeling software systems. Data Acqulsltlon and Processing: The State of the Art With the development of digitally controlled marine gravity systems as described by LaFehret the restrictions of hardware-defined filtering have been removed. This is a major factor in recovering maximum signal in final processed results, by allowing the data processor to quantitatively determine optimum filter parameters for specific sea conditions and induced noise levels. Marine surveys are now routinely producing results of 0.1-0,5 regal resolution over 500 to 1000 meter minimum wavelengths. This change reflects a) the new digital gravity meter technologies, b) benefits of DGPS positioning for the removal of vehicular motion effects on the gravity meter, and c) the benefit of huger, more stable multi-streamer seismic vessels.