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Kinematics and Growth of Supra-Salt Faulting in the Paradox Basin: A Field and Subsurface Analysis

Abstract

Salt can provide the structure and seal necessary for hydrocarbon entrapment, however, it may lead structural complexities, such as compartmentalizing a hydrocarbon reservoir through supra-salt faulting. Outcrop analog studies provide exceptional opportunities to observe how salt-influenced fault geometries evolved spatially and temporally. The Paradox Basin in southeastern Utah is an example of a salt-influenced petroleum basin where the petroleum system is directly associated with evaporites. Decades of petroleum exploration in the region have yielded in a broad subsurface dataset (e.g., seismic reflection data and well penetrations), with close proximity to world-class outcrops. Exposed supra-salt fault scarps have preserved kinematic evidence which provide tangible evidence to populate kinematic models that quantify the temporal and spatial evolution of this fault system. This study focuses on the Salt Valley salt wall, the northernmost and largest salt structure within the northern Paradox Basin. A 40 km long supra-salt fault array trends parallel to and detaches downward onto the NW-plunging salt wall. Through the use of 3D seismic reflection data, wells, published maps, satellite imagery, and a collection of structural field measurements, we are able to build a database that was used to make an integrated interpretation of the spatial and temporal evolution of the fault array. Several kinematic analyses coupled with detailed geometric fault descriptions were used to determine the growth history of the studied fault array that consists of a series of overlapping fault segments up to 12.5 km long, with throws of hundreds of meters, defining a series of crestal grabens and half-grabens. Secondary faults of similar length are present on the flanks of the salt wall. Along the strike of the fault array, there are notable changes in the dip direction of the half-graben master faults and regions of varying fault strikes. These changes reflect heterogeneities of the top-salt geometry. Fault linkage analyses such as: fault throw-length (T-L); throw-distance (T-x); throw-depth (T-z), as well as qualitative distribution of fault throws from map and strike views show that these segments are over-displaced, with a complex fault segment linkage history. We hypothesize that these over-displaced faults evolved with a hybrid fault growth model, where they initiated as isolated fault model but spent the majority of their growth history through coherent fault growth.