Dimensional and Mechanical Stability Analysis of Caves in Bahia, Brazil

Abstract

The interest in carbonate lithologies has risen in the last few decades, due to discoveries of giant and supergiant carbonate reservoirs. While studying the properties of this lithology, the existence of cave systems at great depths was highlighted, since their presence can lead to drilling related problems, as well as change the flow direction of fluids in the subsurface. The possibility of predicting their orien- tations, dimensions and mechanical stability in the subsurface would therefore be of great help in the hydrocarbon business, which is why in this study, thanks to data provided by a Lidar laser scanner, a dimensional analysis of caves’ conduits related to their position within the karst system is performed. The origin of caves can be hypogenic or epigenic and they can present different patterns of distribution of conduits. When deformation events cause the generation of orthogonal sets of joints in the rock layers and fractures intersect with each other and with bedding planes, the fluid flow in the subsurface becomes channelized into these features. The combination of this and speleogenetic processes leads to the development of maze caves, whose conduits’ dimensions vary within a system as a consequence of differences of continuity and connectivity along a fracture network. Variations in the shapes of caves’ conduits can be observed as well, depending on the supply of sediment and the position relative to the water table during dissolution. Mechanical deformation of karst systems can be simulated by using the linear elastic deformation mathematical model. In this way it is possible to study the influence that mechanical properties such as Young’s modulus and Poisson’s ratio have on the mechanical stability of caves in the subsurface.