Detection of brine plumes in an oil reservoir using the geoelectric method EOR designs, using geoelectric measurements

BONGIOVANNI, MARÍA VICTORIA; OSELLA, A.,; DE LA VEGA, MATIAS; TICHNO, ADRIÁN

JOURNAL OF GEOPHYSICS AND ENGINEERING

IOP PUBLISHING LTD

Lugar: Londres; Año: 2013 vol. 10 p. 1 - 10

1742-2132

During water injection in a reservoir at the secondary recovery phase, the oil is replaced by salt-saturated water, producing different saturation zones in the formation containing this reservoir. This process could be optimized if the direction of the fluids could be monitored. Since there are large contrasts in the electric conductivity between salt-water and oil, geoelectrical methods could provide a water saturation map in a given moment of the production. The case we study here corresponds to a rather shallow reservoir (between 500 and 600 m in depth); being the wells on productions, electrodes for borehole measurements cannot be introduced. Hence, our objectives were to determine the possibilities of detecting the direction of channeling of saline water between injection and producing wells, applying the method placing electrodes on surface or even buried, but at depths corresponding to shallow layers. We first designed an electrical model of the reservoir and then we numerically simulated the geoelectrical response, in order to determine the conditions under which the anomaly, i.e. the accumulation of brine in a reduced area, can be detected. The problem to solve is a case of a very conductive anomaly, embedded in an also conductive medium, and whose dimensions (area and thickness) are much less than the depth at which it is located. We used the code Abaqus, which is a general-purpose Finite Element program which support refined meshes with a large number of cells. Four different electrode configurations, Wenner, Schlumberger, Pole-Pole and Pole-Dipole, were considered, embedding the electrodes at different depths. For each case, we compared the potentials at the nodes corresponding to the location of the electrodes with the value obtained for the layered model (without anomaly); we considered that the anomaly could be detected when the differences in the potentials were larger than 10 mV. We found that the channeling of the brine can be detected for the reservoir studied here, if the electrodes are placed at 180 m-deep, being the Wenner configuration, using sixteen electrodes, the one which provides the best resolution. An advantage of burying the electrodes is that the responses are not influenced by weather/environmental effects, and then the observed changes in the voltage should be due quite exclusively to the movements of fluids. Then, a monitoring of the voltage at a number of electrodes embedded at rather shallow depths (from the technical-logistic point of view) could give information about the direction of the saline channeling even if a quantitatively image the subsoil cannot be obtained due to the reduce number of electrodes used in the study.