Controle estrutural e estratigrafia mecânica do carste hipogênico em análogos de reservatórios carbonáticos na formação salitre, Bahia

Abstract

Understanding the karstification process is a key fator in development and exploiting fractured and karstified reservoirs. The karstification process develops caves that influence the flow of fluids. However, these are sub-seismic structures that are difficult to detect with conventional prospecting methods, and their occurrence and geometry are a challenge. This study focused on Neoproterozoic caves of the Salitre formation, northeastern Brazil, in order to understand the relationship between structural settings, petrophysical and petrographic properties with the development of karst structures. For this, we used a multidisciplinary and multiscalar approach using high resolution imaging by Laser Detecting and Ranging (LiDAR), structural geological survey, linear scanlines, stratigraphic analysis, uniaxial compressive strength test, mercury intrusion porosimetry, petrographic analysis in thin sections, scanning electron microscope and x-ray diffractometry. We found that the occurrence of caves is related to fold axis that act as corridors for the flow of fluids. Due to the low porosity and permeability of these rocks, the fluid flow tends to follow the secondary porosity formed due to fracture corridors that form parallel to the fold hinge. With intense flow in this region, karstification is intensified, providing the occurrence of caves. Its geometry is related to the composition of the rocks. Layers with low occurrence or absence of stylolites and with the presence of siliciclastic material suffered a lower karstification. On the other hand, layers with a greater number of stylolites, with thicker stylolites and absence of siliciclastic material, suffered greater karstification intensity. The findings presented here help to predict the occurrence of karst structures and their geometry, with direct application in the understanding of carbonate reservoirs and aquifers.