There are thousands of poorly documented or undocumented oil and gas wells scattered across the country, creating serious public safety and environmental issues. Improperly plugged or unplugged abandoned wells, either oil wells (production or injection) may provide a conduit for migration of contamination or hydrocarbons or injected fluids into fresh water formation. For this reason, all abandoned wells should be located and their condition assessed.
Abandoned wells are usually concealed below the ground surface, and/or they are in remote areas. Direct excavation to find these wells is impractical over large areas, so abandoned well searches depend heavily on non-invasive techniques. These include methods for locating wells by searching historical records and reconnaissance of the area. Geophysical methods, especially magnetic and electromagnetic conductivity techniques have been used to locate abandoned wells successfully
The focus of this research is in three-fold: 1) to apply electrical resistivity imaging over two blown-up production wells in order to determine the geophysical signatures of the metal casings and the subsurface geology impacted by the mixture of fluids of brine and hydrocarbon due to the blow-ups; 2) resistivity imaging surveys were conducted in the vicinity of two already known abandoned, production wells, which were located in central Texas and central Louisiana. The subsurface data suggest that these wells had leaked brine through their well casings; 3) and finally to apply the resistivity technique to two abandoned production wells without any brine contamination issues that have been properly plugged and showed no leakage history.
The resistivity anomalies in the vicinity of the abandoned wells have been attributed mostly to the metallic well casings for convenience, and are not accepted as representative of the near-surface geology. Thus the purpose of this research is to shed some lights into this controversial subject.
Primary Author / Conference Presenter:
Dr. Mustafa Saribudak
Environmental Geophysics Associates
Austin, Texas, USA