Drilling muds are used in oil, gas, and geothermal well drilling, and fluid loss and filter cake formation are critical issues related to successful operations. Also, the filter cake formation and fluid loss are affected by high pressure and high temperature (HPHT) in the borehole. Rate and total fluid loss from drilling mud can affect the performance of the drilling mud and well safety. Hence, it is critical to quantify not only the rate of fluid loss process but also the changes in the filter cake formation during the fluid loss process. Past studies have assumed that the permeability and solid fraction in the filter cake remained unchanged during the formation of the cake and the fluid loss was directly propositional to the square-root of time (API Model). In the experimental part of this study, fluid loss tests were performed for 420 minutes on 2 percent and 8 percent bentonite drilling muds at 100 psig pressure and 100°C temperature. A new kinetic hyperbolic model was developed based on satisfying the basic governing conditions during fluid loss and assuming that the permeability and solid content during the filter cake formation changes with time, temperature and pressure. The new kinetic model was verified with results from various HPHT fluid loss studies reported in the literature and HPHT experiments performed during this study. The new kinetic model prediction was also compared to the API model, and it predicted both short-term (up to 30 minutes) and longterm fluid losses very well. Hence, the new kinetic model can be used to better model the filter cake formation and filter loss in real time as functions of changes in permeability and solid content in the filter cake.

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.

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.