Abstract

Sandstones that overlie or that are interbedded with thick halites commonly contain numerous localized fracture domains that cover areas up to a few tens of square kilometers in extent. The fractures formed due to extension of the sandstones when anticlines were formed during upwelling of the salt in diapirs and pillows. The geometries of the different fracture domains in Jurassic sandstones at Salt Valley Anticline illustrate this relationship, suggesting cause and effect between anticline development and extension fracturing during mobilization of the thick salts in the underlying Paradox Formation. Although each fracture domain contains consistent fracture patterns, the strikes and patterns vary considerably between domains as a result of stresses that varied both temporally and aerially during the multiple events of anticline development. Transitions between domains may be gradual, abrupt, or overlapping. Fracture and fracture-domain patterns allow reconstruction of the general outline of anticline development. Reservoirs in such settings have a high probability of containing numerous intersecting fractures.