The Role of Thermal Conductivity, Structural Framework and Filling Pattern in the Heat Flow Propagation through the Solimões Basin, Northern Brazil

Deep structures, mainly composed of structural lows NE-striked, probably associated with an early extensional evolution in the Solimões Basin, can be recognized through potential field methods, in few seismic lines, as well as in some wells that reached these sequences. The stratigraphic pattern of these wedges and their lithologic fill characteristics are still unknown due to low seismic resolution in deep parts of the basin, partially caused by more than 1000 meters of diabase intrusions, stacked in 3 main levels within the basin. The heat transfer from the basement to the surface crosses these wedges and propagates through a basically sag Paleozoic sequence, causing several pull-ups and pull-downs in the isotherms. It also causes anomalies in heat propagation and consequently in the predicted calibration maps (e.g. Sweeney & Burnham %Ro maps). Additional complexity is added due to emplacement model considered in the modeling process. Three levels of diabase intrusions are considered to be placed at 200 Ma ago, reaching temperatures of around 900 oC and propagating heat through a halite/anhydrite rich sequence below the lower intrusion. The main expected source rock sequence, located at the base of the paleozoic sequence, is affected by both heat flow coming from basement, as well as heat transfer due to intrusion. Then, the understanding of the contribution of each heat source is a crucial step to the maturation prediction. Several synthetic 3D models were carried out in order to establish the relationship between the effect of lithologic variation (sandy, sandy-shaly and shaly fill profiles) in deep structures and the heat transfer through basin. The main conclusions point to a significant effect in the vertical heat profile and subsequently, in the overlapping source rock sequence maturation, caused by the presence of these wedges. This effect is proportional to the volume of the wedge fill (width and depth), thermal conductivity of the sediments, as well as the laterally contrast of the thermal conductivity between the sediments and the basement. Alternative scenarios of the wedge sedimentary fill were tested in the actual modeling simulations. It points to different maturation results at source rock level and contributes to reveal the exploratory uncertainty in thermal complex areas.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California