Using surface downhole ERT for detecting contaminants in deep aquifers due to the exploitation of oil reservoirs

Abstract

The exploitation of a hydrocarbon reservoir, whether conventional or unconventional, may cause environmental damages. Even though sink wells used by oil companies are located much deeper than aquifers, they may eventually contaminate the water with brine leakage, oil spill or other polluting agents, such as chemicals used in hydraulic fracturing. This makes vulnerability studies extremely important. In this work we aim to detect and characterize contaminations of an aquifer that lies above an oil reservoir, at approximately 250 m depth, using current injections on the surface and voltages sensors in the well. At that depth, it is not usual to use downhole measurements to monitor a contaminated aquifer. This is the reason why we want to establish if it is possible to identify the contamination of a part of the aquifer using surface-downhole measurements. In order to achieve this we have designed an electrical model of the reservoir including the contaminated aquifer with either a conductive or resistive contamination such as saline brine, oil spill or CO2, and numerically simulated the forward and inverse geoelectrical responses. Numerical results show that the detection of the contamination is possible only with the surface-downhole configuration. This fact is a clear evidence of the advantage of implementing this kind of ERT configurations in order to detect and possibly characterize contaminated deep aquifers.