DEVELOPING EFFICIENT METHODS TO LOCATE LEGACY OIL AND GAS WELLS

The purpose of this project is to develop an efficient method to locate legacy oil and gas wells using an Overhauser magnetometer. Extensive research (e.g. Kang, et al., 2014) has shown that legacy/abandoned oil and gas wells can be potentially hazardous to the environment by leaking methane to the surface and/or contaminating shallow groundwater. In Arkansas, most plugged wells have all surface equipment removed leaving no visible trace at the surface and thus making the environmental assessment of these wells difficult. Using a magnetometer, magnetic anomalies from the metal casing can be detected in the general areas of suspected wells. In order to assess large numbers of wells, the typical anomaly size is critical to minimize magnetometer field work time. Little information exists on the size of these associated anomalies, therefore the primary purpose of this project was to define the typical anomaly size so as to optimize transect spacing and limit excessive time in the field. Here we show the results of five wells with a survey grid at two meter spacing. The average anomaly size was determined and transects with wider spacing were used to create additional grids to test the maximum transect size that can still detect the anomaly. Our preliminary results indicate that magnetometer surveys are an efficient tool to locate abandoned wells.