Modelling the Impact of Abandoned Wells on the Gulf Coast Aquifer in Texas

Abstract:

Over the years, many oil and gas wells have been abandoned, without proper plugging, around homes, farms, industrial sites, and urban areas. These abandoned wells are becoming potential groundwater contamination sources that could leak hydrocarbon to the subsurface aquifer units. When screened to multiple aquifer units, abandoned wells may also allow deeper salty aquifers to pollute shallow freshwater aquifers. Primary goal of this research is to create a risk map for the Gulf Coast Aquifer (GCA, area: 108 x 10³ km²) in Texas showing locations that are prone to groundwater contamination due to existence of abandoned oil and gas wells. The GCA is extended over 56 counties parallel to the coastline of Gulf of Mexico from Louisiana border to the border of Mexico. The GCA represents a major aquifer that is being used for municipal, industrial, and irrigation purposes. It contains confined and unconfined units (e.g., Chicot, Evangeline, Jasper) that dip toward the Gulf of Mexico. The number of oil and gas wells in the GCA is estimated at 278,151 of which 1,709 are abandoned. In this study, we developed a four-class risk map that shows areas of low, marginal, severe, and very severe risks due to presence of abandoned wells within the GCA. We used weighted overlay and weight of evidence models in a Geographic Information Systems (GIS) environment to define the risk controlling factors and their significance and weights such as well locations, surface and subsurface lithology, geologic structures, aquifer thickness, aquifer depth, stream density, and rainfall. Our research results could be utilized by decision makers to develop enhanced mitigation scenarios for risks associated with abandoned wells in Texas.