Dexin Liu

Conventional solid-weighted drilling fluids suffer from particle settling under high-temperature and high-pressure (HTHP) conditions and easily induce irreversible reservoir pore damage, limiting safe drilling in deep HTHP reservoirs. To address these drawbacks, two solids-free water-in-oil emulsion drill-in fluid systems based on GTL synthetic oil and saturated potassium formate brine were developed using composite ET/MT emulsifiers. The thermal stability, HTHP filtration, droplet size, interfacial rheology, clay inhibition, and permeability recovery performances were systematically evaluated. The 45:55 oil/water formulation exhibited excellent long-term thermal homogeneity, whereas the 20:80 system achieved higher density. The optimized emulsions presented low HTHP fluid loss, stable interfacial films, prominent clay inhibition, and over 90% core permeability recovery, demonstrating favorable reservoir protection capacity. Molecular dynamics simulations qualitatively clarified the interfacial adsorption behavior of composite emulsifiers and the formation of compact interfacial films. Notably, most tests were single determinations without replicates, blank core controls were absent, and bulk rheological data were unavailable, leading to qualitative mechanistic analysis. This work verifies the feasibility of the proposed solids-free fluid system, while further replicated tests and complete parameter validation are essential for its quantitative performance interpretation and field application.

To mitigate weighting-agent settlement, reservoir pore-throat plugging, and water-sensitivity damage during deep high-temperature drilling, a solids-free high-density oil-based drill-in fluid was developed using synthetic base oil as the continuous phase and potassium formate brine as the dispersed phase. Within the formulation range investigated, the optimized system employed 75 wt% potassium formate solution and a GMS/SDS compound emulsifier at a mass ratio of 9.7:0.3, corresponding to an HLB value of 4.5. Two representative formulations were evaluated: System I, with an oil/water ratio of 20:80, 5% emulsifier, and a density of 1.35 g/cm³; and System II, with an oil/water ratio of 15:85, 10% emulsifier, and a density of 1.46 g/cm³. Both systems maintained favorable electrical stability and filtration performance after thermal treatment at 150 °C, with sedimentation factors of 0.505–0.507 after 72 h of static aging. Molecular dynamics simulations suggested that the co-adsorption of GMS and SDS at the oil/brine interface, involving hydrogen bonding and ionic interactions, may contribute to interfacial-film stabilization, consistent with the experimental observations. Formation-damage tests using three sandstone cores covering low-, medium-, and high-permeability levels yielded permeability recoveries of 92.8–96.2% under the tested conditions. The formulation also exhibited an anti-swelling rate close to 100%, tolerance to the investigated contaminants, and a P110 corrosion rate of 0.042 mm/a. These results demonstrate the feasibility of the proposed solids-free high-density oil-based formulation within the investigated composition range and laboratory conditions, while its long-term performance and applicability under more severe HPHT and field conditions require further validation.

Pure-phase Fe3O4 catalysts are promising for heavy-oil viscosity reduction because of their low cost and high activity, but their practical application is limited by facile sintering and mass-transfer constraints. Herein, OV-Fe3O4/NC was developed by dispersing Fe3O4 on porous pyridinic-N-doped biochar and regulating the surface electronic structure through oxygen-vacancy engineering. The resulting catalyst achieved a 86.4% viscosity reduction in field heavy oil, markedly outperforming pure-phase Fe3O4 and the blank system. It also gave a higher yield of light hydrocarbon gases, while NH3 was detected only in the OV-Fe3O4/NC system, indicating enhanced bond cleavage and molecular reconstruction of heavy-oil macromolecules.Characterization results confirmed that Fe3O4 nanoparticles were uniformly anchored on the hierarchically porous biochar surface. XPS and EPR further verified the introduction of oxygen vacancies after annealing, accompanied by coordinated changes in the Fe valence states and surface oxygen environment of Fe3O4. Combined FTIR, radical-quenching, and supercritical water experiments suggest that viscosity reduction via upgrading mainly proceeds through alkyl radical-induced β-scission. In this process, OV-Fe3O4/NC promotes the formation of radicals and active hydrogen species as well as hydrogen termination, thereby enhancing bond cleavage and stable conversion of heavy components while suppressing radical condensation and coke formation, thus achieving a better viscosity reduction of heavy oil via upgrading.

A novel efficient barium sulfate scale inhibitor was designed by examining important quantum parameters such as adsorption energy, solubility, steric hindrance parameter, and entanglement molecular weights. Through molecular simulation techniques, it was found that the carboxylic acid group of the scale inhibitor molecule could transfer an average of 0.07 e⁻ electrons to the barium sulfate surface. During molecular dynamics simulations, closer adsorption between oxygen atoms and barium ions in the scale inhibitor was observed, which resulted from van der Waals forces. Based on the simulation results at the molecular level, we successfully prepared this scale inhibitor by free radical polymerization and verified its high efficiency in our experiments: the scale inhibition efficiency was as high as 89.1% when used at a concentration of 160 mg/L under the conditions of pH = 7 and 70 °C. In addition, by SEM and XRD analyses, we further confirmed the consistency of the scale inhibition mechanism of the scale inhibitor with the molecular simulation results.

The formation of barium sulfate scale is a persistent and formidable challenge across various industrial processes. In order to effectively mitigate this problem, this study proposed the development of an innovative azacrown ether-based macrocycle descaling agent. Using density functional theory, an in-depth analysis of the surface energy of different barium sulfate crystal facets was carried out, together with a detailed investigation into the adsorption properties of the functional groups on the (001) surface. A further comprehensive investigation was carried out to determine how changes in the nitrogen and oxygen atoms in the crown ether framework influence its adsorption affinity to barium ions. In addition, a detailed analysis was carried out to elucidate the molecular interactions between crown ethers with pyridine carboxylic acid side chains and barium sulfate. The newly developed decalcifying macrocycle descaling agent exhibited superior adsorption performance, achieving an adsorption energy for barium ions approximately −4.1512 ev higher than that of conventional DTPA decalcifiers. This remarkable improvement is mainly attributed to the pivotal role of electrostatic forces in the coordination process between the macrocycle descaling agent and barium ions, with an electrostatic potential value reaching −143.37 kcal/mol. This discovery not only introduces a novel approach to the removal of barium sulfate scale but also highlights the significant potential of macrocycle chemistry in industrial applications.