Behavior of Nano Calcium Carbonate Modified Smart Cement Contaminated with Oil Based Drilling Mud

Abstract

Abstract As oil and gas exploration and production expands around the world, there are unique challenges in well construction beginning at the seafloor. There are several benefits in using oil based drilling mud (OBM) in drilling operations but there are concerns about the potential contamination of the cement. Recent case studies on cementing failures have clearly identified some of these issues that resulted in various types of delays in the cementing operations. For a successful cementing operation, it is critical to determine the contamination of cement during the installation so that necessary remediation can be made to minimize the effect. At present there is no technology available to monitor cementing operations and also to determine the potential of contamination in real time during the installation of the oil and gas wells. In this study, the effect of adding 1percent of nano CaCO3 (NCC) on the smart cement was investigated in order to protect the smart cement against oil based mad (OBM) contamination. Several tests were performed to monitor the changes of the smart cement behavior with 3% OBM contamination and also how NCC can improve the properties of the contaminated smart cement. Variation of electrical resistivity of the smart cement with curing time was monitored from the initial time of mixing to 28 days of curing under water. Adding 1 percent NCC to the smart cement reduced the initial resistivity from 1.07 O.m to 0.85 O.m, a 21% reduction but increased the compressive strength by over 50%. Also addition of nano CaCO3 increased the rheological properties of the cement. With 3% OBM contamination the viscosity of the cement slurries increased. Results showed that contamination of smart cement with OBM reduced the long term resistivity of the smart cement but adding NCC enhanced the electrical resistivity of the contaminated smart cement cured under water. The compressive strength of the smart cement contaminated with 3 percent of OBM decreased by 44% and 3% respectively after 1 day and 28 days of curing. Addition of NCC improved the compressive strength of the 3 percent OBM contaminated smart cement by 72% and 10% respectively after 1 day and 28 days of curing under water. In this study the electrical resistivity index (RI24) was used as an indicator for predict the compressive strength of the smart cement at various curing times. The relationships between RI24 and the compressive strength were linear for the smart cement with and without 1% NCC modification. In order to evaluate the piezoresistive behavior of the smart cement, 0.075 percent (BOWC) of conductive filer (CF) was added to the cement to enhance the piezoresistive behavior of the cement. Results showed that change in resistivity at compressive failure for the smart cement was over 1000 times more than compressive strain and addition of 1% NCC further enhanced it by about 37% after 1 day and 28% after 28 days of curing under water. The OBM contaminated smart cement showed less change in piezoresistivity at maximum compressive stress at failure than the smart cement but addition of 1% of NCC enhanced the piezoresistivity of OBM contaminated smart cement.