Interactive Integrated Interpretation Of Gravity,Magnetic, And Seismic Data: Tools And Examples

Abstract

ABSTRACT Marine geophysical surveys often include seismic-reflection, gravity and magnetic data collected simultaneously by multisensor survey vessels. Integrated interpretation of these data sets provides a synergism which often leads to better resolution of exploration problems. Modern workstations with the appropriate interactive modeling software make the integration process easier, faster, and more interacting. One such program is the interactive proprietary GAMMA (Gravity And Magnetic Modeling Applications) program developed at Chevron by Saad and 8ishop in 1989. The program is unique in its ability to display a migrated seismic section in depth as an overlay on which gravity and/or magnetic models can be constructed and modified interactively, allowing true integration on the workstation. Examples from several offshore areas are presented to demonstrate the importance and power of integration in reducing ambiguities in seismic interpretation. INTRODUCTION Multisensor survey vessels are commonly used in offshore geophysical operations to collect seismic, gravity and magnetic data simultaneously. Modern workstations provide the environment that makes it easy for the explorationist to interpret these data simultaneously using an integrated approach. Integrated interpretation in geophysics implies that all available geophysical and geological data have been integrated into one compatible interpretation. Although gravity and magnetic data can be interpreted independently, their interpretation is more affective when considered in conjunction with seismic, drilling, and other geological information. Seismic data interpretation, in turn, can benefit greatly from integration with potential field data; this is emphasized by the examples presented in this paper. Integration of geophysical data can range from simple visual inspection of the data (QUALITATIVE integration) to detailed analysis and full integration of the data (QUANTITATIVE integration). The latter relies heavily on modeling and can be easily and interactively performed in the modern environment of workstations. This paper describes the means and mechanics by which interactive modeling software has been used in geophysical integration and presents several examples from actual case histories in offshore areas to demonstrate the importance of integration. The examples include modeling of overhung salt domes, tabular salt masses, and complex over thrust geology. Other applications include differentiation between salt/shale diapirs and igneous basement uplifts, definition of over pressured shale masses and delineation of sand-filled channels. TOOLS FOR GEOPHYSICAL INTEGRATION Modern workstations and interactive modeling software provides the environment and tools that make it easy for the explorationist to integrate various geophysical and geological data sets. The GAMMA program developed at Chevron by Saad and 8ishop in 1989 is an example of such tools. It is a user-friendly, highly interactive, fast 2-D/2.5D gravity and magnetic modeling program. One of the goals in the development of this program was to provide the capability for interactive integration of gravity and magnetics with seismic data. The program can read in files from other programs, thus providing easy access to seismic date, seismic models, and other interpretation data which does encourage integration. MEANS AND MECHANICS OF INTEGRATION There are basically three ways by which geophysical integration can be achieved within the interactive workstation environment.