Using Simulation to Address Challenges of Subsalt Imaging in Tertiary Basins with Emphasis on Deepwater Gulf of Mexico
Authors: Fehler Michael 
Published: April 2012

Geophysical imaging and subsurface characterization for offshore petroleumexploration and reservoir characterization face increasingly demandingrequirements for reliability and for providing increased information about theearth's subsurface. New methods for data acquisition, data processing andsimultaneous analysis of multiple types of geophysical datasets (e.g. seismic, EM, gravity) are helping to meet these challenges but there is need to testthese methods and to quantify their robustness. Testing and evaluation of newmethods can be done using simulated benchmark datasets provided the simulationsare calculated using realistic models and that the simulation methodology iswell validated. The benchmark datasets must not only be reliably calculated butthey must be sufficiently large to mimic state-of-the-art fieldacquisitions.

The SEG Advanced Modeling Project (SEAM), using funding provided by theResearch Partnership to Secure Energy for America (RPSEA), has developed amodel for a deepwater region that contains a major salt body and severalpetroleum reservoirs located around and beneath the salt. Constructing andconducting geophysical simulations on the model is a challenge for currenthigh-performance computing technology. A suite of geophysical simulations isbeing conducted on the model including acoustic-wave, Tilted TransverseIsotropic acoustic, Gravity, Controlled Source Electromagnetic, Magnetotelluricand Elastic. Geophysicists are actively using these datasets to facilitatetheir development and testing of new algorithms and acquisition schemes forbetter subsurface characterization. The access to large multidisciplinarydatasets calculated on a single realistic model developed for a deepwaterregion like the Gulf of Mexico has long been desired to allow testing andbenchmarking of geophysical techniques, testing of new data acquisitionschemes, and assessing the value of multi-disciplinary inversion approaches.SEAM is seeking to provide these datasets for the geophysical community.

Introduction

Geophysical imaging continues to undergo transformation as new data acquisitionand processing schemes allow increasingly complex regions of the earth's crustto be imaged with better and better resolution. Advances from ray-basedmigration methods to one-way wave propagation migration and now reverse timemigration have been made possible by the availability of faster computers thathave sufficient memory to hold large models that the methods require forsuccessful application. Advances in data acquisition have provided an enormousincrease in the amount and quality of data that are available to input into thenew imaging schemes. The ability to implement imaging approaches that are basedon more than the isotropic acoustic velocity of the earth have led tosignificant improvements in image quality and the type of information that canbe obtained from images. For example, Controlled-Source Electromagnetic (CSEM)data have been found to provide valuable information not only when usedindependently of other data but also have recently been found to add tremendousvalue to interpretation when used in combination with seismic data. The recentuse of anisotropic earth models that have not only a vertical axis of symmetry, so-called vertical transverse isotropy or VTI, but that that now have aspatially-varying non-vertical axis of symmetry (Tilter Transverse Isotropy, TTI) have led to better images of complex regions like the Gulf of Mexico andprovide the opportunity to provide constraints on geomechanical models of theregion.