Characterizing Smart Cement Modified with Flyash and Metakaolin
In this study, real time monitoring system based on electrical resistivity was used to monitor the smart oil well cement modified with fly ash and metakaolin up to 50 and 10%, respectively. Initial resistivity of the smart cement was around 1.12 Ω.m. Modifying the smart cement with 50% fly ash, increased the initial resistivity to 1.53 Ω.m, a 36% increase. Modifying the smart cement with 10% metakaolin increased the initial resistivity by 12% to 1.26 Ω.m.
The thermal conductivity of smart cement with water to cement ratio of 0.38 varied from 0.87 w/m.k to 0.67 w/m.k after 28 days of curing. Addition of 50% fly ash decreased the thermal conductivity from 0.67 w/m.k to 0.3 w/m.k after 50 days of curing and decreased the strength by 14%.
Addition of metakaolin to the smart cement had minimal effect on thermal conductivity but increased the compressive strength from 6200 psi to 7000 psi after 28 days of curing. Addition of metakaolin to the smart cement had minimal effect on thermal conductivity but increased the compressive strength from 6200 psi to 7000 psi after 28 days of curing.
Large-model test was done to demonstrate real time monitoring the cement operation. Piezoresistivity behavior of the smart cement modified with fly ash and metakaolin was studied under various loading conditions up to 28 days of curing. It was observed that resistivity changed by 250% and 12% under compressive and tensile loading, respectively. Partially replacing cement with fly ash increased the piezoresistivity up to 340% and also decreased the degradation of cement in sulfuric acid solution with pH of 1. Addition of 50% fly ash decreased the 28-day compressive strength. Adding 10% metakaolin increased compressive strength by 13% and also increased the modulus slightly. Direct tensile strength was 23% and 87% lower than the splitting tensile strength and flexural tensile strength, respectively. Bonding strength between cement and casing were investigated through testing and modeling. Bonding strength between cement and casing was around 80 psi after 28 days of curing. Contamination of cement with 2% salt increased the compressive strength by 23% after one day and decreased by 23% after 28 days of curing.