QUANTIFYING STRAIN ACCOMMODATION AND DEFORMATION OF WALL ROCKS AND OVERBURDEN SEQUENCES PROXIMAL TO SALT DIAPIRS IN SALT VALLEY, UTAH

Many of the largest hydrocarbon reservoirs in the world are found in contractional fold belts, where salt or mud has mobilized to form diapirs. When diapirs are active, the stresses exerted on surrounding materials can create high strain zones in overburden, and materials that are proximal to diapir walls. Strain can be accommodated in these areas by compaction of unlithified or poorly lithified sediments, and the creation of deformation bands in surrounding porous materials. When zones of deformation bands are pervasive, they affect the strength and permeability of their host rock and can baffle the flow of hydrocarbons in potential reservoirs. Therefore, it is crucial to understand the spatial distribution and frequency of deformation bands in potential hydrocarbon reservoirs near diapirs. Salt has traditionally been viewed as largely passive in these systems, with surface-directed salt flow and diapir growth driven by gradients in deposited sediment thickness. However, recent numerical modeling has demonstrated that mobilized salt has the strength to actively deform cover rock sequences. These models produce a finite plastic strain gradient, with strain values greater than 200% near salt walls, and reducing to 100% approximately 1.5 kilometers from active diapirism. If such “active” diapirism creates strain gradients, the surrounding rocks should exhibit a reduction in porosity and permeability due to plastic pore collapse, which could eventually lead to development of deformation bands. This study investigates the spatial distribution and frequency of deformation bands found throughout the Salt Valley anticline, and adjacent areas near Arches National Park, Utah. These predicted zones of deformation bands are abundant on the flanks of the Salt Valley anticline, which is one of the best natural laboratories in the world for studying diapirism-related deformation. Preliminary work, including detailed mapping and microstructural analysis, shows abundant deformation bands proximal to salt walls becoming less frequent as distance from salt diapirs increases. Future work will focus on mapping transects perpendicular to the Salt Valley diapir, where detailed mapping and rigorous sample collection will show the distribution of diapirism-related deformation bands in the study area.