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Fault Pattern in the Southern Campos Basin, Brazil: 3-D Seismic Insights and Implications for Albian Carbonates of the Macae Group


Listric normal faults played a major role in the structural framework of post-salt reservoirs in Campos Basin, Brazil, by trapping hydrocarbons in rollover systems due to its geometry. Although also occur several factors such as basement pre-existing structures, extension mechanisms (rifting), overburden thickness and overall structural style, the salt movement is the main mechanism for the overall post-salt fault pattern. This study focuses on understanding the relation between the fault pattern related to salt tectonics and the distribution of carbonates of the Albian Macae Group. To do so, we used a 1.050-km2 3D seismic survey, in the southern Campos Basin, and derived discontinuity seismic attributes to characterize the fault pattern. The identified fault types include: (1) listric, (2) growth-fault systems, and (3) high-angle normal fault. The faults are grouped into three trends: (1) WSW-ENE (striking N70-80°E), (2) NE-SW (striking N45-50°E), and (3) NNE-SSW (striking N15-20°E). The structural and stratigraphic patterns are summarized in six tectonic-stratigraphic units (TSUs): (1) rollover and tilted block systems, (2) growth extensional wedge, (3-4) extension by a main growth-fault system, (5) normal-faulted blocks, and (6) highly-faulted and fractured graben area. TSU1 is formed by frequent listric faults with rollover systems characterized by differential extension, recognizable in the seismic reflectors. TSU2 is characterized by an overall prograding pattern with dipping reflectors. TSU3 is composed of the main growth-fault rooted at the top of the salt, which appears to be accommodating syn-tectonic growth strata. TSU4 is structurally constrained by the outer limit of NNE-SSW and WSW-ENE fault sets, which separates the prograding wedge from the package mostly controlled by the main growth-fault system. TSU5 is affected by the normal-faulted blocks with uniform extension, creating a stepped pattern in the sedimentary package. TSU6 is highly affected by high-angle faults and a high density of fractures, which makes interpreting and establishing a relation between fault structures and seismic units a challenge due to the noisy seismic character. To summarize, the structural style of the Albian interval has correlation with salt-related and basement-inherited structures and is characterized by a normal and listric fault pattern, dipping basinward and rotating strata landward, trending dominantly NE-SW, parallel to basement major extension axis.