Report on variation of electrical conductivity during steam injection in unconsolidated sand saturated with a salt solution

Abstract

The spatial and temporal variation electrical conductivity in saturated sands during steam injection has been measured and modeled. Experiments consisted of introducing steam into an end of a tube filled with a sand saturated with a slightly saline solution. Measurements of electrical conductivity were then made every 10 seconds at 10 locations along the tube using a four electrode technique. After injection a steam condensation front forms ahead of the steam front that separates the mixed-phase steam zone from the liquid zone. Conductivity measurements at a specific position in the tube throughout time show that the electrical conductivity starts at a constant value, decreases before the steam front arrives and then, immediately prior to the steam front arrival, goes through a maximum before dropping by a factor about 25. These variations can be explained by first: a dilution of the interstitial solution ahead of the steam front thereby causing the initial drop in conductivity; second, an increase in temperature of the solution immediately prior to the arrival of the steam front causing the conductivity maximum; and finally the large drop in conductivity due to the combined effects of a decrease in saturation and dilution of the residual liquid in themore » two-phase zone. Mathematical solutions of a set of differential equations that take into consideration all of these effects are presented. These solutions reproduce the significant features of the conductivity data, and help to explain the physical phenomenon. The study suggests that the measurements of changes in the subsurface conductivity field during steam injection operations may indicate the location of ionic concentration, temperature, and steam saturation fields.« less