Seismic data conditioning for identification of Sand Dunes in the Early Jurassic Nugget Formation in the Moxa Arch

Abstract

The Moxa Arch has been an important geologic structure for hydrocarbon exploration since the mid- 1940s in the Green River Basin. It is also recognized by the US Department of Energy as one of two carbon sequestration sites within Wyoming. The early Jurassic Nugget formation within the Moxa Arch is a possible reservoir for carbon sequestration however past drilling may have compromised it as such. The Nugget formation is an eolian sandstone that was deposited as part of the early Jurassic sand sea that covered Arizona, Utah, and southwestern Wyoming. Seismic attribute analysis shows the presence of northwest-southeast trending linear geologic features believed to be eolian dunes and inter-dunal deposits. Previous works, using outcrop study, on the Nugget formation have measured a northeast-southwest general paleo-wind direction during the time of deposition. The Petrophysical analysis of three surrounding wells also shows that the eolian sands have high porosity resulting in low impedance, while the inter-dunal deposits, composed of halite and anhydrite, are impermeable barriers and have high impedance. Furthermore, the structure-oriented filtering (SOF), when applied on the prestack data during seismic processing, improves the overall data quality and increases the resolution of the discontinuities seen in the coherence based attributes. After SOF, the time slices look sharper with preserved discontinuities and suppressed acquisition footprints. Analysis of co-rendered coherence and curvature clearly displays the extent and nature of the eolian dunes within the 3D volume. The seismic attribute analysis on the lineaments and the Ant Track workflow on the curvature attribute shows that the average paleo-wind direction was around N-225 degrees E which supports the previous outcrop studies.

AAPG Datapages/Search and Discovery Article #90343 ©2019 AAPG Southwest Section Annual Convention, Dallas, Texas, April 6-9, 2019