Influence of Humidity, Moisture and Temperature on the Electric Properties of Self-Sensing Cement Pastes for Post-Abandonment Well Monitoring

The self-sensing capability is a well-studied property of carbon nanotubes blended cement pastes intended for civil construction applications. Nevertheless, most of the studies that can be found in the literature were performed at room temperature, natural humidity and atmospheric pressure. It is necessary to understand how down-hole conditions affect the electrical response of this intelligent material to identify its potential application in the oil industry. This paper presents a study on the effect of relative humidity, internal moisture and temperature on the electric properties of self-sensing cement pastes. These pastes were manufactured with class G cement blended with carbon nanotubes and are intended to be used as an intelligent material capable of auto monitoring its internal stresses and deformations during the post-abandonment phase of a well. Carbon nanotubes blended cement pastes were molded in 2.5 × 2.5 × 11.5 cm3 prisms embedded with copper electrodes. The produced samples were exposed to different relative humidity, internal moisture and temperature conditions and their electrical resistivity was measured at each condition by connecting a DC power supply and a multimeter to the embedded electrodes. Relative humidity and temperature was varied in a climate chamber, already internal moisture was varied by saturating and partially drying the material. It was found that the electrical resistivity of the studied pastes is more highly sensible to internal moisture and temperature, while relative humidity had a lower effect under the studied conditions. These results lead to the conclusions that the electrical response of carbon nanotubes blended pastes is highly affected by environmental conditions, and that for oil-well applications it is necessary to develop correction models that allow an accurate measurement of the internal stresses and deformations of the material.