Portland cement hydration in the vicinity of electrically polarized conductive surfaces

Hardening of Portland cement-based materials in vicinity of electrically conductive surfaces, especially when the surfaces are electrically or galvanically polarized, can lead to both morphological and chemical changes in cement close to the surfaces due to combined electrochemical and electrophysical processes. Cement hydration products close to graphite and steel surfaces being positively (anode) and negatively (cathode) electrically polarized (direct current) were studied. Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy were used to compare structure and atomic composition of cement hydration products on cathode, anode and a reference surface with no electrical polarization. The application of direct current (DC) potential in aqueous Portland G cement dispersion significantly affects cement hydration products close to cathode and anode and different products were found at the anode compared to the cathode surfaces. At the graphite anode, calcium sulphate crystals along with calcium hydroxide were most abundant, while the graphite cathode was mainly covered with calcium hydroxide. The calcium hydroxide carbonated upon exposure to air during drying. When steel electrodes where used, the most significant adsorption occurred at the anode, in contrast to graphite where the largest amount of the adsorbed material was found on the cathode. The observed differences were explained in view of electrophysical (electrophoresis, electroosmosis) and electrochemical (reduction and oxidation) processes occurring at electrode surfaces upon application of DC current. The knowledge gained in this work is important for engineering of electrically conductive cement nano-composites where typically the contact surface of an electrically conductive filler and a cementitious matrix is high.publishedVersio

Nanorubber-modified cement system for oil and gas well cementing application

Flexible cement systems with low shrinkage are more capable than the conventional cement systems to withstand the tensile stresses generated by fluctuation of temperature and pressure in oil and gas wells. In this work nanorubber particles (NR), stable at high temperature and in alkaline environment, were incorporated into a cement system. The impact of NR on the heat of hydration, autogenous shrinkage and tensile properties were measured at 40 °C, whereas the sonic compressive strength development and 3 days tensile strength were measured at 20.7 MPa and 142 °C. Addition of NR to the cement system resulted in reduced autogenous shrinkage, but also retarded setting time and compressive strength development. Incorporation of NR into the cement system improved the capacity to withstand tensile stresses at laboratory conditions. The results indicate promising performance at well conditions, which is supported by a measured positive impact on tensile strength at high temperature and pressure

Portland cement hydration in the vicinity of electrically polarized conductive surfaces

Hardening of Portland cement-based materials in vicinity of electrically conductive surfaces, especially when the surfaces are electrically or galvanically polarized, can lead to both morphological and chemical changes in cement close to the surfaces due to combined electrochemical and electrophysical processes. Cement hydration products close to graphite and steel surfaces being positively (anode) and negatively (cathode) electrically polarized (direct current) were studied. Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy were used to compare structure and atomic composition of cement hydration products on cathode, anode and a reference surface with no electrical polarization. The application of direct current (DC) potential in aqueous Portland G cement dispersion significantly affects cement hydration products close to cathode and anode and different products were found at the anode compared to the cathode surfaces. At the graphite anode, calcium sulphate crystals along with calcium hydroxide were most abundant, while the graphite cathode was mainly covered with calcium hydroxide. The calcium hydroxide carbonated upon exposure to air during drying. When steel electrodes where used, the most significant adsorption occurred at the anode, in contrast to graphite where the largest amount of the adsorbed material was found on the cathode. The observed differences were explained in view of electrophysical (electrophoresis, electroosmosis) and electrochemical (reduction and oxidation) processes occurring at electrode surfaces upon application of DC current. The knowledge gained in this work is important for engineering of electrically conductive cement nano-composites where typically the contact surface of an electrically conductive filler and a cementitious matrix is high

Electrokinetics Application in Concrete and Well Construction

Electrically induced or coupled transport processes including electrophoresis, electroosmosis and electromigration in solutions and porous media under an external electric field have been extensively studied and employed in many disciplines. For protection and rehabilitation of concrete structures, cathodic protection, electrochemical realkalization, and chloride extraction are extensively used. Other electrokinetic techniques are developed for the concrete industry, but have not been widely used so far, including electrokinetic treatment processes, for corrosion mitigation, recovery from sulfate attack, crack healing, and porosity and permeability reduction. These processes can improve the microstructure of the cement-based systems resulting in an improved performance in long-term and can be applied to repair failed structures. Application of electrokinetic processes are rapidly extended in well construction due to the increased interest in techniques enabling manipulation of micro- and nanosized particles. The techniques could be beneficial in building a robust cement sheath in oil and gas wells. Additionally, electrokinetic remediation techniques can possibly be introduced for repairing damaged structures in oil and gas wells. This review provides an overview of electrokinetic-based techniques, which has been introduced to cement-based materials, mainly reinforced concrete. The potential application of these techniques in oil well construction is discussed

Cement sheath modification using nanomaterials for long-term zonal isolation of oil wells: Review

Well cementing is an important operation during drilling and completion of oil wells. The cement sheath must maintain well integrity behind the casing and provide long-term zonal isolation to ensure safety and prevent environmental problems. Despite recent technological advancement in smart polymeric materials, fibers and self-healing materials, it is still a big challenge to provide adequate long-term zonal isolation in severe oil well conditions. This review provides an overview of challenges faced in oil wells compromising the long-term ability of the cement sheath to provide zonal isolation. Factors controlling the long-term performance of cement sheath are discussed, in terms of shrinkage, tensile strength and flexibility. The use of nanomaterials as cement additive to fabricate flexible, high-tensile strength, and low-shrinkage cement system are reviewed. Introduction of nanomaterials into the cement system is a promising approach to design a sealant for the entire life of the well, thereby avoiding potential remedial costs and environmental impacts

Effect of electric field on push-out strength of cemented steel pipes

Cement-steel interfacial strength is an important measure for estimating the robustness and hydraulic sealing ability of wells. In this paper, laboratory experiments were performed in which small steel pipes (10 mm in diameter) were cemented in place within a Portland cement slurry under application of constant electrical potential difference between the pipes. The objective was to investigate whether there might be an observable difference between push-out strengths obtained with the pipes of different polarity (anode vs. cathode vs. reference nonpolarized pipe). The duration of the potential application and the magnitude of the potential difference were varied between the tests. The experiments demonstrated that at the higher potential difference (4 V), the duration of potential application had a noticeable effect on interfacial bonding. Application of 4 V for 24 h resulted in loss of bonding at cement-cathode interface, which could be attributed to massive water transportation to the cathode region by small radii cations. At the lower applied potential difference (1 V), there is an improvement in push-out strength at anode at short duration of potential application. This could be due to pore filling by precipitation of expansive minerals in pores and cement particles migration toward anode. The effect of potential on push-out strength in a hardened cement suggests that low potential difference applied for a short period of time might improve cement-steel interfacial strength

Effect of electric field on push-out strength of cemented steel pipes

Cement-steel interfacial strength is an important measure for estimating the robustness and hydraulic sealing ability of wells. In this paper, laboratory experiments were performed in which small steel pipes (10 mm in diameter) were cemented in place within a Portland cement slurry under application of constant electrical potential difference between the pipes. The objective was to investigate whether there might be an observable difference between push-out strengths obtained with the pipes of different polarity (anode vs. cathode vs. reference nonpolarized pipe). The duration of the potential application and the magnitude of the potential difference were varied between the tests. The experiments demonstrated that at the higher potential difference (4 V), the duration of potential application had a noticeable effect on interfacial bonding. Application of 4 V for 24 h resulted in loss of bonding at cement-cathode interface, which could be attributed to massive water transportation to the cathode region by small radii cations. At the lower applied potential difference (1 V), there is an improvement in push-out strength at anode at short duration of potential application. This could be due to pore filling by precipitation of expansive minerals in pores and cement particles migration toward anode. The effect of potential on push-out strength in a hardened cement suggests that low potential difference applied for a short period of time might improve cement-steel interfacial strength