Soft Sediment Deformation and Injectites in the Jurassic Carmel Formation, Southern Utah: Implications for Reservoir Characterization

David Wheatley
University of Utah, Department of Geology and Geophysics
Salt Lake City, UT, USA
[email protected]

Numerous, well-exposed sandstone injectites or clastic pipes in fluvial to sabkha facies of the Jurassic Carmel Formation of southern Utah record evidence of extensive liquefaction from strong ground motion. Approximately 900 separate injectities of tens of centimeters to meter scale diameters were mapped in three separate sites covering a 6.5 by 5.5 km area. The pipes crosscut predominately sandstone with some thin mudstone beds with extensive evidence of contemporaneous volcanic activity.

These clastic pipes form through liquefaction, which occurs under a unique set of circumstances including a high water table, which saturates a body of unconsolidated sand beneath capped by a lower permeability, confining layer. The liquefaction likely occurred in one major event sourced from local fluvial sandstones. These pipes are closely tied to the complex interplay between sabkha and fluvial depositional environments along with a high water table, with pipe alignment approximately parallel to the paleoshoreline.

Within petroleum reservoirs, injectities can act as fluid pathways through fine-grained rocks. Injectities form high porosity conduits, which allow migration pathways through what would otherwise be a flow barrier. The Carmel pipes show characteristic bleaching to indicate diagenetic movement of reducing fluids through the pipe conduits. The injectite mapping demonstrates relationships of size hierarchy within injectite clusters and the internal spacing and self-organization. Measurements of size and distribution, in addition to porosity and permeability measurements, give accurate analog data to populate injectite-bearing reservoir models. This study uses analog data to create a predictive field-scale model for fluid flow in clastic pipe reservoir systems.

AAPG Search and Discovery Article #90183©2013 AAPG Foundation 2013 Grants-in-Aid Projects