Eolian facies in the Barra de Itiúba Formation: example of a potential deep reservoir

Abstract

Located in the Sergipe-Alagoas Basin, the Barra de ltiúba Formation is a recognized hydrocarbon/gas source rock and reservoir. In the Alagoas Regional Low it appears as a thick packet of interbedded sandstone and shale of deltaic origin. A core sample from well 1-MAS-1-AL reveals a subarkosic eolian lithofacies ai the -4,351.5/-4,369.5 m waler-bearing interval. This lithofacies is associated with a channel lithofacies, which is probably of a deltaic distributary. The two lithofacies display average porosity values of 11.5% (eolian) and 8.2% (channel) and average permeability values of 13.2 mD and 4.8 mD. Textural aspects seem to have favored the development of slightly higher porosity and permeability values in the eolian facies. Main porosity is secondary and resulted from the corrosion of framework grains and from the solution of both feldspar grains and, local/y, carbonate cement. Both primary and secondary porosity were preserved thanks to the relative compositional and mechanical stability of the quartz-rich framework. The feldspars played a special role in the development of pore space, as they averted compaction at the initial stage of diagenesis and kept the pathways of fluid circulation open. Later, pore space was created through solution of the framework. In characterizing the eolian lithofacies in the Barra de Itiúba Formation and measuring the porosity at a depth of over 4, 000 m, this study has identified a new exploratory frontier in the Sergipe-Alagoas Basin.