Structural kinematics and salt evolution in the

Abstract

Seismic acquisition, seismic processing (PreSTM and PSDM), seismic interpretation, velocity modeling (for depth-to-time as well as time-to-depth conversion) and sequential restoration are all essential steps to illustrate the geometrical evolution of a very complex area located on the Mexican southeastern portion of Gulf of Mexico. This study uses all 5 approaches to improve the understanding of the tectonic evolution of the area as well as the implications for petroleum prospectivity in the area. The study area presents a complex three-dimensional geometry, which is related to the complex evolution of the Gulf of Mexico, from a rifting stage during the Triassic to Middle Jurassic, the deposition of the Callovian salt, a passive margin stage during Late Jurassic to Late Cretaceous and a compressional stage from Late Cretaceous to Recent. In addition, salt withdrawal was related to the formation of important depocenters and gravitational movement of the Cenozoic deposits. Sequential restoration resulted in valuable insights into: (1) The structural evolution of the salt and overburden; (2) Qualitative rates for several processes such as sedimentation rate, salt withdrawal as well as salt-rise: (3) Prediction of shape and depths of the seafloor paleogeoraphy; (4) Position of several petroleum generating systems (such as the most important the Tithonian generating system) through the time (especially during the time of generation and expulsion of hydrocarbons); (5) Location of several reservoir rocks as well as seal rocks through the time; (6) Time of formation of traps at the different levels of the geologic column. (7) Timing and possible pathways for hydrocarbon migration (at least in 2D). Limitations and errors during the entire workflow from seismic processing to section restoration arise. The most important are: (1) Errors during the PSDM seismic processing such as the use of the wrong velocity field, etc., (2) The seismic interpretation itself; (3) Errors during velocity model to depth-to-time conversion as well as time-to-depth conversion; (4) Cross-section orientation; (5) Assumption of plane-strain deformation, when actually there is movement out of the plane. (6) Errors calculating decompaction as well as isostatic corrections; (7) Wrong utilization of restoration algorithms to model actual rock deformation and faulting. Regardless of all the listed limitations and errors, experience has shown that the errors are relatively minor. Therefore, restoration is a powerful tool even in salt basins. An analysis of the evolution of the area as well as its petroleum system implications was based on the restoration of a 2D regional cross-section (57 Km length). Important conclusions regarding to the structural evolution of the area as well as its implications for petroleum prospectivity are accomplished. First, Mesozoic traps have low risk of hydrocarbon charge since traps were already formed by the time of hydrocarbon generation and expulsion as well as its proximity with the Tithonian source rock. Second, Tertiary traps have higher risk than Mesozoic due to the important amount of salt that was sealing this stratigraphic level during part of the Miocene. However, as salt evacuated, and with the formation of a regional weld, the opportunities to charge these Tertiary traps increased. In addition, since migration is a three-dimensional phenomenon, lateral migration must occurred increasing significantly the chance for hydrocarbon charge. Finally, 3D restoration will help to understand such convoluted geometries, especially when there are several strain directions as well as complex salt movement in the area.