Shaocong Pang

In this study, we systematically evaluated the fluid loss reduction effect of four nanomaterials in high-temperature water-based drilling fluids. Compared to the natural polymer PAC, the synthetic acrylamide-based polymer-maintained integrity and reduced fluid loss from 36.25 mL to 14 mL after aging at 180 °C, while forming a thinner and less permeable filter cake. Among the nanomaterials tested, 0.5 wt.% TiO ₂ showed the most significant fluid loss reduction after aging at 180 °C, significantly optimizing the particle size distribution and reducing the fluid loss. When the polymer was used in combination with TiO ₂ , a significant synergistic enhancement was observed, which reduced the fluid loss to a minimum value of 11.6 mL at 180 °C. Zeta potential, particle size analysis, and SEM images showed that the effect resulted from the improved colloidal stability, closer packing of the particles, and the formation of a dense filter cake structure. The results show that the nanomaterial-polymer composite system can significantly improve the high-temperature fluid loss reduction performance of drilling fluids through the dual mechanism of physical blocking and chemical interaction, which provides an effective strategy for the design of high-performance fluid loss reduction agents.

The development and utilization of geothermal resources are effective ways to alleviate the current haze situation, adjust the energy structure, and achieve energy conservation and emission reduction. Geothermal formations typically contain extensive fracture networks, with fracture openings. These fracture networks can result in substantial losses of the drilling fluid and increased costs for geothermal drilling. Temporary plugging cements are used to solve the problem of lost circulation due to their high strength and high acid solubility. In this paper, two types of temporary plugging materials, magnesium oxysulfate (MOS) cement and magnesium oxychloride (MOC) cement, were prepared. The influence of the plugging agent on the flow field and the force exerted on the solid under the action of the fluid was analyzed using fluid-solid coupling software. The simulation results show that when subjected to a flow rate of 10 m/s, the edge of the cement experiences a significant force, while the stress is not widely transmitted to the middle and rear of the cement. This indicates that the cement has a strong resistance to the fluid flow. The fundamental characteristics of MOC cement and MOS cement, such as compressive strength and setting time, were investigated. The test results show that adjusting the molar ratio of the two types of cements can shorten the setting time by 60% and increase the compressive strength to up to 23 MPa. In addition, the acid solubility of the cement with different ratios of raw materials is above 95%. The plugging performance of these two cements as loss circulation materials was evaluated by using a physical simulation device. The pressure bearing capacity of the MOC cement with different MgO/MgCl₂·6H₂O/H₂O molar ratios ranged between 13.4 and 23.6 MPa. The maximum bearing capacity of the MOS cement can reach up to 18.6 MPa. The results showed that both cements possess excellent plugging and pressure bearing capacity.