Abstract

Teapot Dome, Wyoming, also known as National Petroleum Reserve 3, is a candidate for a national CO₂ storage test site. The oil field in Upper Cretaceous sandstones at Teapot Dome was discovered in the 1880’s based on surface occurrences of a waxy hydrocarbon, “ozokerite”, within calcite-lined fractures. The goal of this research is to determine if the hydrocarbons resulted from active (i.e. present-day) seepage of the oil reservoirs or from an older episode of local or basin-scale fluid flow.

Two generations of fractures and two separate calcite cementation events are recognized in outcrop, and hydrocarbon wax, likely ozokerite, post-dates both calcite generations. The calcite contains two-phase (liquid-vapor), secondary hydrocarbon fluid inclusions that fluoresce a blue-white color in UV epi-illumination. The ozokerite also fluoresces blue-white, which suggests that petroleum inclusions and the hydrocarbon wax are related. Gas chromatograms (GCs) of ozokerite are consistent with GCs of oils from Upper Cretaceous reservoirs at Teapot Dome, indicating that a connection between the fractures and a hydrocarbon reservoir did exist.

Secondary hydrocarbon inclusions are present in the calcite, which indicates that active oil migration occurred while the fractures were at higher temperatures than surface conditions. Therefore, the oil was emplaced within the fractures when they were between 600 to 1500 m deep. Furthermore, the ozokerite formed during the uplift and exhumation of the Upper Cretaceous strata at Teapot Dome. The fractures in this study have no active connection to any deeper oil-bearing strata.

First posted 2006