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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.

The study described in this paper involved a close examination of one of the least-researched cement phases, 4CaO•Al(2)O(3)•Fe(2)O(3) (C(4)AF or ferrite). The two ferrite materials used in this program were: (1) extracted from an industrial clinker free of 3CaO•Al(2)O(3) (C(3)A or aluminate); and (2) a laboratory-synthesized C(4)AF compound. Both ferrite materials were initially characterized using optical microscopy, x-ray diffraction (XRD), and Raman spectroscopy. The hydration kinetics and reactivity of both materials were studied with a calorimetric technique. Similar to aluminate, ferrite also demonstrated a strong early hydration rate. An adequate amount of sulfate (SO(3)) was needed to regulate the ferrite hydration rate. Based on this work, an equivalent aluminate content, C(3)A(eq), is proposed. The hydration of C(3)A(eq) needs to be properly controlled with the appropriate amount of sulfate. The concept, based on equivalent aluminate content for cement sulfate optimization, ensures proper early hydration behavior from both C(3)A and C(4)AF and avoids potential cement-admixture incompatibility probems, especially for the cements containing little or no C(3)A content.

A methodology is presented that is particularly useful for evaluating mixture designs and multiple design criteria when predicting the service life of concrete structures. The methodology incorporates surface environment, chloride transport, temperature of surrounding medium, seasonal effects, and construction variability into a model that can be used to predict the service life of a reinforced concrete structure in different environments. Three components (submerged, splash zone, and superstructure) on the same concrete structure in two temperature environments are used in examples to illustrate the technique. Several concrete mixtures of different quality are evaluated in these applications. Silica fume is shown to increase significantly the estimated service life of the structures by decreasing chloride transport in the concrete and by decreasing the buildup of chloride in the near surface region of the structure.

A methodology is presented that is particularly useful for evaluating mixture designs and multiple design criteria when predicting the service life of concrete structures. The methodology incorporates surface environment, chloride transport, temperature of surrounding medium, seasonal effects, and construction variability into a model that can be used to predict the service life of a reinforced concrete structure in different environments. Three components (submerged, splash zone, superstructure) on the same concrete structure in two temperature environments are used in examples to illustrate the technique. Several concrete mixtures of different quality are evaluated in these applications. Silica fume is shown to increase significantly the estimated service life of the structures by decreasing chloride transport in the concrete and by decreasing the buildup of chloride in the near surface region of the structure.

New construction or repair of existing structures dealing with the placement of concrete underwater poses certain challenges that require special placement techniques, and more specifically, specialized mixture proportions. Anti-washout admixtures (AWA), based on water-soluble polymers of various types, have been developed for use in concrete placed underwater in order to minimize cement washout and provide in-place concrete of satisfactory quality. These admixtures create a cohesive paste phase either by binding free mix water or by enhancing interparticle attraction. Hence, they are finding additional uses such as segregation or bleed control agents, and viscosity modifiers. Recently, the need for a viscosity modifying agent arose in a dam rehabilitation project in Alabama where a grout curtain was being placed to control seepage under the dam. To verify the feasibility of using an AWA in the grout mixtures for this project, a preliminary study was performed in the laboratory to investigate the performance of fluid grouts treated with a unique cellulose-based liquid AWA developed for underwater concreting. The effect of this unique AWA on the plastic properties of fluid and flowable grouts are presented in this paper. The results indicate that it is possible to use this admixture to modify grout viscosity, minimize bleeding characteristics, and improve washout resistance of fluid and flowable grout mixtures. Applications that might benefit from these improvements include: grouting riprap in tidal zones; and placement of grout curtains to minimize water seepage under dams.

In the present study, an extensive test program is conducted to measure and compare the heat of hydration obtained from both calorimeter and ASTM C186-05 test methods. A statistical analysis is performed to evaluate the variations of the test data. The results indicate that the isothermal conduction calorimeter method is a more reliable, less time-consuming, and less labor-intensive method than the ASTM C186-05 test method. The heat of hydration at 3 days showed the least variation in all calorimeter tests. These suggest that ASTM shall consider adopting the isothermal conduction calorimeter method for measuring the heat of hydration of cement. The 3-day heat of hydration value can be used for specifying the limit of heat release for type II cements.

An experimental investigation was conducuted to assess the effects of calcium chloride, calcium nitrate, and sodium nitrite on pore solutions chemistry and their relationship to corrosion of steel in concrete. The possibility of an ion-exchange mechanism between ingressed chloride ions and complex admixed ions also was investigated. The results indicated that the concentration of admixed ions in the aqueous phase (pore solution) decreased significaltly with time. Thence, it is speculated that these cheimcals at commonly used dosages are unlikely to promote or inhibit corrosion of reinforcing steel in concrete very significantly. It was found that no ion exchange occurred between ingressed chloride ions and bound admixed anions.

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.