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

GRÜNHUT V.; BONGIOVANNI M. V.; OSELLA, A.

NEAR SURFACE GEOPHYSICS

EUROPEAN ASSOC GEOSCIENTISTS & ENGINEERS

Lugar: Houten (Holanda); Año: 2018

1569-4445

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 thewater with brine leakage, oil spill or other polluting agents, such aschemicals used in hydraulic fracturing. This makes vulnerability studies extremelyimportant. In this work we aim to detect and characterize contaminations of anaquifer that lies above an oil reservoir, at approximately 250 m depth, usingcurrent 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 thecontamination of a part of the aquifer using surface-downhole measurements. Inorder to achieve this we have designed an electrical model of the reservoirincluding the contaminated aquifer with either a conductive  or resistive contamination such as saline brine, oil spill or CO2, andnumerically simulated the forward and inverse geoelectrical responses. Numericalresults show that the detection of the contamination is possible only with the surface-downholeconfiguration. This fact is a clear evidence of the advantage of implementingthis kind of ERT configurations in order to detect and possibly characterize contaminateddeep aquifers.