Evaluating Hydrocarbon Migration Paths Using Fault Displacement Distributions
The analysis of displacement distributions on an extensional faults system is explored to evaluate hydrocarbon migration paths in a productive area located on the northern flank of the San Jorge Basin, Argentina. In this area, most hydrocarbon traps are located in the footwall of north-dipping normal faults, where reservoirs are folded and sealed against low permeability-hanging wall units. Postulated charging mechanisms include lateral migration from a proven southward kitchen and vertical migration through faults from a hypothetical deep-seated local source pod.
The throw of the reservoir section has been measured along 123 seismic sections, crossing a total of eighteen faults, six of which accounts for most of the total displacement. Additionally, five levels were mapped over the deep and shallow segments along the main faults.
Single fault throw profiles are symmetric with greater values at its center and zero at the fault tips. Fault-displacement contours have elliptical shapes with maximum values centered at the reservoir section. Some faults have a deep segment with another zone of maximum displacement that has both lateral and upwards gradients to zero. The aggregated throw profile shows three sectors with displacement variations that are similar to those of a single isolated fault. These sectors are separated by an accommodation zone formed by an overlapping belt of relay ramps, and by a transfer zone with high angle faults that served as magmatic conduits.
Displacement-fault length plots suggest that isolated faults may have linked early in the propagation history. At the same time, transfer zone development facilitates the emplacement of igneous dikes and sills. Oil and gas bubble maps show that both fault juxtaposition seals and igneous dikes have acted as barriers for south to north horizontal migration. This configuration made possible the charge of existent fields but risked the charge of traps located behind the barriers and far from the kitchen.
Displacement contour maps reveal that faults initially nucleated close to the reservoir section and propagated downwards, but did not connect with pre-existent faults. Consequently, vertical migration from a hypothetical deep-seated source pod seems to be unlikely.
AAPG Search and Discovery Article #90166©2013 AAPG International Conference & Exhibition, Cartagena, Colombia, 8-11 September 2013