Field test for real time monitoring of piezoresistive smart cement to verify the cementing operations

In this study, a field well was installed and cemented using the smart cement mixture with enhanced piezoresistive properties. The field well was designed, built, and used to demonstrate the concept of real time monitoring of the flow of drilling mud and smart cement and hardening of the cement in place. The well was installed in soft swelling clay soils to investigate the sensitivity of the smart oil well cement. A new method has been developed to measure the electrical resistivity of the materials using the two probe method. Using the new concept, it has been proven that the resistivity dominated the behavior of drilling fluid and smart cement. LCR meters (measures the inductance (L), capacitance (C) and resistance (R)) were used at 300 kHz frequency to measure the changes in resistance. The well instrumentation was outside the casing with 120 probes, 18 strain gages and 9 thermocouples. The strain gages and thermocouples were used to compare the sensitivity of these instruments to the two probe resistance measure in-situ in the cement. The electric probes used to measure the resistance were placed vertically at 15 levels and each level had eight horizontal probes. Change in the resistance of hardening cement was continuously monitored since the installation of the field well for over 100 days. Also, a method to predict the changes in electrical resistance of the hardening cement outside the casing (Electrical Resistance Model - ERM) with time has been developed. The ERM predicted the changes in the electrical resistances of the hardening cement outside the cemented casing very well. In addition, the pressure testing showed the piezoresistive response of the hardened smart cement and a piezoresistive model has been developed to predict the pressure in the casing from the change in resistivity in the smart cement.