Smart Cement Piezoresistivity Characterization with Sodium Metasilicate under Temperature and Curing Environments for Oil Well–Cementing

Abstract

The smart cement behavior with 0.3% sodium metasilicate (SMS) at 80°C (176°F) under two different environments was investigated in this study. The smart cement was made using the class H oil well cement and 0.1% conductive filler to make it a bulk chemo-piezoresistive material with highly sensing property. The smart cement was cured in air and also submerged in water-saturated sand at 80°C up to 28 days. The smart cement initial resistivity (ρo) decreased from 0.97 to 0.87 Ω·m with 0.3% SMS, a 10% decrease. Similarly the minimum resistivity (ρmin) decreased from 0.81 to 0.72 Ω·m with 0.3% SMS, an 11% decrease, which is an indication of the chemo-resistivity of the smart cement. The resistivity changes were higher than the unit weight changes in the smart material. The resistivity of the smart material oven cured in saturated sand at 80°C was 55 to 75% less than the resistivity of the material cured at 80°C after curing for one, seven, and 28 days. The material resistivity with 0.3% SMS cured in both conditions were about 25–55% less than the smart cement only. The resistivity with curing time under different curing conditions was modeled using a nonlinear curing model, and the prediction agreed well with experimental results. Also, a nonlinear power relationship was used to relate the resistivity to the weight change in the cement. The smart cement cured at high temperature (80°C) showed piezoresistive response under applied stress. For the smart cement the piezoresistivity at compressive strength changed from 245 to 475%. With 0.3% SMS the chemo-piezoresistivity at compressive strength varied from 160 to 345% based on the curing time and curing environment, which is an indication of the chemo-piezoresistivity of the smart cement. The smart cement cured in saturated sand showed higher piezoresistivity, about 15–25% more compared to the dry curing. Since the failure strain for the smart cement was only 0.2%, the piezoresistivity at peak compressive stress of the smart cement has been enhanced by more than 900 times, making it highly sensing. The compressive stress resistivity constitutive model predicated the material behavior very well. Also, a hyperbolic model was used to predict correlation between materials properties and also changes with curing time investigated in this study.