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• Development of CNTs-composite cement for geothermal exploitation. • Evaluation of the synergy enhancement properties of consolidation/thermal conductivity of CNTs-composite cement for geothermal exploitation. • Investigation on the synergy enhancement mechanism of consolidation/thermal conductivity of CNTs-composite cement for geothermal exploitation. Geothermal well is completed generally with a cemented casing across the heat source, while the existing casing cement generally suffered from insufficient performance to meet the demand of actual medium-deep geothermal well construction. In view of this, combining theoretical analysis and experimental research, a new type of carbon nanotubes (CNTs) composite cement for geothermal exploitation was successfully developed by introducing thermal conductivity fillers, heat stabilizing material, nanomaterial and additives to synergistically regulate the comprehensive performance of casing cement. The evaluation of the high-temperature rheology and stability of slurry, and the compressive strength and thermal conductivity of cement stone was carried out based on the normative means. And the results showed that cement slurry had excellent high-temperature performance. The 28d compressive strength (With the curing condition of 150 °C & 20.7 MPa) of cement stone reached 8.15 MPa and the thermal conductivity was stabilized at 2.236 W/(m·K), both of which were at a high level in similar studies. Finally, a combination of hydration process analysis (TGA and XRD), microstructure study (MIP and SEM) and heat transfer mode study (Energy spectrum scanning) was used to summarize the nano-composite cement consolidation/thermal conductivity mechanism. Analysis showed that CNTs could play the effect of "pore filling" and "bridging" hydration products, and the additives could participate in the hydration reaction and regulate the hydration process. In addition, the heat transfer mode of the cement matrix was in accordance with the theory of heat conduction path. The study results provide a new idea to improve the cementing quality of cement and optimize the heat extraction efficiency of geothermal wells from the perspective of material development. [ABSTRACT FROM AUTHOR]

The following study is focused on the suggested strategy to attack a problem of Shallow Gas/Water flow are drilled and cemented without equipment to prevent blowouts in offshore fields. We analyze historical cases where abnormal pressure water sands observed in the resistivity log were not identified in the Pressure While Drilling tool. The event flow was observed by the remotely operated vehicle. We suggest a decision tree when a shallow gas/water flow unexpected. Such events cause an uncontrolled flow situation by placing at risk the safety of persons working in the maritime unit drilling, the same unit and economic losses for the execution of unplanned operations. [ABSTRACT FROM AUTHOR]

• Development of graphene-composite cement material for geothermal exploitation. • Evaluation of the hydration and thermal conductivity property of graphene-composite cement for geothermal exploitation. • Investigation on the hydration and thermal conductivity mechanism of graphene-composite cement for geothermal exploitation. In the process of geothermal exploitation, the thermal conductivity of casing cement affects the heat exchange efficiency of geothermal wells to a great extent. Because of this, combining with theoretical analysis and experimental study, this paper documented the development of a graphene-composite cement material for geothermal exploitation, based on the evaluation of thermal conductivity property and its hydration mechanism. Cement additives, including NS-600 and 1200 mesh silicon carbide (SiC) as basic thermal conductive fillers, graphene nanosheets (GNSs) aqueous solution for synergistic thermal conduction, and early strength agent (ZQ-4), structural stabilizer (FL-5), defoamer (MC-6) were utilized. The rheological properties, stability, compressive strength, and thermal conductivity of cement slurry were evaluated by laboratory instruments. X-ray diffraction (XRD) and environmental scanning electron microscope (ESEM) were used to analyze the phase composition and micro morphology of the optimized formulas, and the hydration and thermal conductivity mechanism of the graphene-composite cement was obtained. The thermal conductivity of the two optimized formulas obtained in the experiment were 2.141 W/(m · K) and 1.862 W/(m · K) respectively. The study results provide a new method to improve the properties of potential casing cement for enhancing the heat exchange efficiency of deep geothermal exploitation. [ABSTRACT FROM AUTHOR]