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Study of the Sand Dunes in the Early Jurassic Nugget Formation in the Moxa Arch of Wyoming Using Seismic Attributes and Petrophysical Modeling

Abstract

Study of the Sand Dunes in the Early Jurassic Nugget Formation in the Moxa Arch of Wyoming using seismic attributes and petrophysical modeling

Dhruv Agarwal1*, Sumit Verma1, and Subhashis Mallick2

1Geology Program, The University of Texas of the Permian Basin, Odessa, Texas, USA

2Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming, USA

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 and Navajo Sandstone (equivalent of Nugget) 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 evaporites and carbonates, are impermeable barriers and have high impedance. Analysis of co-rendered coherence, curvature and P-impedance clearly displays the extent and nature of the eolian dunes within the 3D volume. The seismic facies attribute calculated by using the Self Organizing Maps (SOMs) algorithm also

confirms the presence of more sand facies on top and more evaporite/carbonate facies at the bottom of the Nugget Sandstone Formation. The paleo-wind direction was calculated based on these NW-SE trending lineaments delineated from the seismic attributes and found to be going from NE to SW, matching the outcrop studies being done earlier for the same formation.