Print this pageReducing Uncertainty in Subsalt Interpretation: A Non-Seismic View from Integration
Significant hydrocarbon discoveries have been made in subsalt structures, and the potential for further discoveries is driving exploration after risky targets. However, salt formations are challenging geophysical interpretation issues and need to be addressed properly. In this paper we discuss how non-seismic data can be integrated in the cycle of iterative depth migration and model updating leading to better seismic imaging results and a more reliable prospect evaluation.
Especially areas involving complex salt geometries as in the Gulf of Mexico or offshore Brazil are affected by issues limiting the success of pre-stack depth migrations, e.g. reduced data quality, incorrect structural concepts, unresolved geometries or inaccurate velocities. Our approach to tackle these problems is the integration of data from independent geophysical techniques, which are linked to the same lithological model but respond to different geophysical properties, like density, susceptibility or resistivity.
Key ingredients for a successful application of this concept - besides a reasonable seismic coverage - are: adequate high-resolution non-seismic data, constraining geological boundary conditions, a flexible software environment for integrated 3D modeling, inversion and visualization, experienced interpreters with excellent inter-disciplinary communication skills, - and a proven workflow, adjustable to the specific project requirements.
Having gravity, magnetic, gravity gradient, EM and/or magnetotelluric data at hand, a typical study starts with a coarse evaluation of their usability for the given objectives and expected targets, particularly with regard to the availability of a-priori information. Further workflow steps include qualitative and quantitative data analysis, the initial model construction with respective sensitivity tests, and a geostatistical approach for defining property relationships. The main project phase consists of cooperative PreSDM and non-seismic interpretation, aiming to define an integrated model with improved geometries and reduced uncertainties, in order to minimize exploration risk.
We will present examples from different regions where multi-disciplinary 3D modeling helped to delineate the allochthonous salt distribution. As in many cases, the base of salt could not be clearly identified from seismic data, but the integrated approach revealed its geometry and salt thickness; a major step for better imaging of target structures below salt.
AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil