Fracture-related Fluid Flow in Sandstone Reservoirs - Insights from Outcrop Analogues of South-eastern Utah

Fault- and fold-related fractures influence the fluid circulation in the subsurface, thus being of high importance for CO2 storage site assessment, especially in terms of reservoir connectivity and leakage. In this context, discrete regions of concentrated sub-parallel fracturing known as fracture corridors are inferred to be preferential conduits for fluid migration. We investigate fracture corridors of the middle-late Jurassic Entrada and Curtis formations of the northern Paradox Basin (Utah), which are characterized by discoloration (bleaching) due to oxide removal by circulating CO2- and/or hydrocarbon-charged fluids. The analyzed structures are located in the footwall of a km-scale, steep normal fault with displacement values on the order of hundreds of meters. They trend roughly perpendicular and subordinately parallel to the main fault direction, and define a systematic network on the hundreds of meters scale. The fracture corridors pinch- and fringe-out laterally and vertically into single, continuous fractures, following the axial zones of open fold systems related to the evolution of the main fault. Based on the presented data we hypothesize that such fracture corridors, connecting localized reservoirs at different stratigraphic levels up towards the surface, represent preferred fluid migration pathways rather than the main faults.