Electrical conductivity of steam-flooded, clay-bearing geologic materials

The effect of clay content on the electrical response of steamflooded geologic material is studied using a combination of laboratory experiments and numerical simulations. The presence of clay can increase the conductivity of a steam zone by providing a surface conduction path that is enhanced strongly by temperature increases. Clay also increases the residual water saturation in a steam zone, further increasing conductivity. These effects can result in steam zones that are more conductive than initial conditions. However, the presence of clay alone is not sufficient to make all portions of a steam zone conductive relative to initial conditions. Equally important to the electrical behavior is the fluid response of the reservoir to the injection of steam. In particular, the speed of the steam front, relative to the speed of the liquid water in the steam zone, plays a key role. Relatively fast-moving steam fronts cause distilled water banks to form around the front. This leads to steam zones with electrically resistive forward sections, even in clay-rich material. The rear sections of these steam zones can be either resistive or conductive, depending in part on the clay content and the salinity. Relatively slow-moving steam fronts do not cause distilled water banks to form and allow the formation of steam zones that are completely conductive relative to initial conditions. These experimental results demonstrate the potential complexities in steam-flood electrical data. The numerical method used in this study can be used to help interpret those complexities.