Timing of hydrocarbon emplacement in ozokerite andcalcite lined fractures, Teapot Dome, Wyoming

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 basinscale 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 bluewhite 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. Introduction Teapot Dome and the adjacent Salt Creek field were found on the basis of surficial hydrocarbon shows (Curry, 1977; Thom and Spieker, 1931; Mills, 1923; Wegemann, 1918). Teapot Dome currently is used as an oilfield technology testing center and may become a test facility for the geologic storage of CO2. A CO2 pipeline serves the enhance oil recovery (EOR) project at the adjacent Salt Creek field, and this pipeline may be extended to bring CO2 to Teapot Dome for storage tests. However, the presence of hydrocarbons within fractures exposed at the surface is problematic for storing CO2 in the subsurface as it indicates that the fractures were at some point connected to a deeper petroleum reservoir. Therefore, baseline and fluid-flow history studies are needed prior to injection of CO2. The USGS has recently conducted a study at Teapot Dome on fluid communication within reservoirs and between reservoirs (Dennen et al., 2005), as well as between subsurface fluids and the surface.