THE EFFECT OF STEAM QUALITY ON THE ELECTRICAL BEHAVIOR OF STEAM-FLOODED SANDS - A LABORATORY STUDY

Laboratory measurements of the effects of steam injection on the elect rical conductivity of sands can aid in the interpretation of electrica l surveys used to monitor subsurface steam-injection projects. The eff ect of variations in injected steam quality was measured in the experi ments presented here. The injection of low-quality steam, boiled from a 0.01 mol/L NaCl solution, into clean sand saturated with 0.01 mol/L NaCl, resulted in a net decrease in conductivity and a constant equili brium conductivity in the steam zone. The injection of high-quality st eam, using the same saturating and injection salinities, caused the co nductivity to first drop to a minimum and then to increase to an equil ibrium value similar to that seen in the low-quality injection. The lo cal conductivity minimum deepened with time and traveled with the stea m front. The appearance of the conductivity minimum at the steam front can be attributed to the formation of a dilution bank, which temporar ily decreases the local salinity. The extent of the dilution increases with time, resulting in the decrease of the conductivity over time. T he conductivity then increases as injected salt moves through the sand . The steam quality controls the appearance of this minimum because it determines the relative speeds of the steam front and the steam liqui d: a minimum will not occur if the steam front moves more slowly than the steam liquid.