Real Time Monitoring of Oil Based Mud, Spacer Fluid and Piezoresistive Smart Cement to Verify the Oil Well Drilling and Cementing Operation Using Model Tests

Abstract

Abstract Well control operations are critical to ensure successful cementing of the oil wells with any losses. With increased drilling depths for production of oil and gas there are greater challenges due changes in the natural geological formations with in situ pressure and temperature conditions. Recent case studies on oil well failures have clearly identified cementing and drilling mud contamination as some of the issues that resulted in various types of delays in the cementing operations. For a successful cementing operation, it is critical to monitor the drilling and cementing operation during the installation so that necessary remediation can be made to minimize the delays and losses of cement. At present there is no technology available to monitor cementing operations without using buried sensors within the cement sheath and also monitor the movement of the drilling mud and spacer fluid to determine the changes real time during the installation of oil or gas wells. In this study, small well models were designed, built, and used to demonstrate the concept of real time monitoring of the flow of smart drilling mud, space fluid and smart cement and hardening of the cement in place. Also, 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 resistivity dominates the behavior of drilling mud 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. Several laboratory scale model tests have been performed using instrumented casing with wires and thermocouples. When the drilling mud was in the model borehole the measured resistance was the highest based on the high resistivity of the drilling mud. Notable reduction in electrical resistance was observed with the flow of spacer fluid and cement. Change in the resistance of hardened cement has been continuously monitored up to about 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.