Analysis of fault leakage from Leroy underground natural gas storage facility, Wyoming, USA

Analysis of fault leakage from Leroy underground natural gas storage facility, Wyoming, USA

Mingjie Chen & Thomas A. Buscheck &

Jeffrey L. Wagoner & Yunwei Sun & Joshua A. White &

Laura Chiaramonte & Roger D. Aines

Abstract Leroy natural-gas storage site is an anticlinal, fault-bounded, aquifer-storage system located in Wyoming, USA. Based on its abundant data, uncontrolled leakage history and subsequent control by the facility operators, a modeling framework was developed for studying reservoir behavior, examining pressure and gas-inventory histories, as well as gas and brine leakage, and evaluating the sensitivity of that behavior to uncertainty about reservoir properties. A three-dimensional model capturing the bounding fault, layered geologic stratigraphy, and surface topography was calibrated by history data of reservoir pressure and gas inventory. The calibrated model predicted gas arrival at the ground surface that was consistent with the timing of observed gas bubbling into a creek. A global sensitivity analysis was performed to examine the parameters inuencing fault leakage, and a geomechanical stability analysis was conducted to investigate the likelihood of fault reactivation. In general, it is shown that a discrete leakage pathway is required to explain the observed gas leakage and its subsequent operational control by reducing reservoir pressures. Specically, the results indicate that fault leakage is a plausible explanation for the observed gas leakage. The results are relevant to other natural-gas storage sites, as well as other subsurface storage applications of buoyant uids, such as CO2.

Keywords Natural gas . Underground storage . Gas leakage . Fault . USA

Introduction

Natural gas underground storage plays a vital role in enabling constant, year-round delivery rates (from gas-supply wells), including during the summer (non-heating season), thereby meeting seasonal demands of the consumer and eliminating shortages during the winter (heating season). Over 13 % (3.1 trillion cubic feet) of annual natural gas consumption is delivered from over 400 storage reservoirs across the United States (Fig. 1). In the next 20 years, the consumption of natural gas is projected to increase by more than 50 % (Kendell 2008). Therefore, there will be a need to develop new gas storage reservoirs, as well as safely maintain current ones.

Three main types of underground gas storage are in use today: depleted gas/oil reservoirs, aquifers, and salt caverns (Lord...