High-salinity produced water is prone to salt precipitation in the gathering and transportation process of oilfields，which affects pipeline transportation safety and system stability. To address salt precipitation in produced water from a high-salinity and high-alkali reservoir in Mabei Oilfield，this study conducted experiments on salt precipitation factors，single-salt critical salinity，and mixed-salt cooperative precipitation experiments，based on produced-water property testing and water-chemistry analysis. The results showed that the salinity of the aqueous phase from Mabei Oilfield is approximately （2.5-3.0）×10⁴ mg/L. The produced water is of the sodium bicarbonate type，and the main ions are Na⁺，CO2-3   ，HCO-3，and Cl^-. The system basically reaches salt precipitation equilibrium  after 20 min of cooling. Sand content of 1%-5% and oil content of 0%-40% have little effects on the critical salt precipitation salinity of the free water phase. The critical salinity of NaCl changes only slightly with temperature，whereas Na₂CO₃ is the most temperature-sensitive salt and is an important driver for salt precipitation. The critical salinity of the NaCl-Na₂CO₃-NaHCO₃ mixed-salt system generally grows with increasing temperature and is significantly affected by salt proportions. A cooperative mixed-salt precipitation model was further established. After interactive correction，the mean absolute error for the D-M mixed-salt system decreased from 10.68% to 6.76%，indicating that the critical salt precipitation salinity of the mixed-salt system is controlled by the Na⁺ common-ion effect，carbonate equilibrium transformation，and high-ionic-strength coupling. The findings of this study provide a theoretical basis for salt precipitation risk prediction and process optimization for the gathering and transportation of high-salinity and high-alkali produced water in Mabei Oilfield.

The narrow annulus in slimhole horizontal wells leads to significant differences in Cuttings transport，compared to conventional horizontal wells. To investigate the cutting transport mechanisms in slimhole horizontal wells，a CFD-based numerical model accounting for drill string eccentricity was developed for solid-liquid two-phase flow in the annulus. This study analyzed the effects of key factors，including flow rates，drill pipe rotation speeds，well inclination angles，and drilling fluid properties，on cutting transport in slimhole horizontal wells. The results showed that increasing the drill pipe rotation speed enhances the tangential and axial velocities of the annular fluid and expands the "viscous coupling" region. This facilitates the upward movement of cuttings from the lower side to the upper side of the annulus，thereby improving transport efficiency. Critical thresholds for "rotation speeds" and "flow rates" were identified in highly inclined sections，where cutting transport becomes the most challenging with the two parameters both below the thresholds，and in horizontal sections，where transport becomes more difficult with the two parameters both exceeding the thresholds. Increasing the drilling fluid density enhances the buoyancy acting on cuttings and reduces deposition. The effects of drilling fluid rheological parameters on wellbore cleanup exhibit non-linear trends，with an optimal range existing under different flow rates and rotation speeds. The findings of this research provide theoretical support for optimizing hydraulic parameters in slimhole horizontal wells and preventing issues like drill string sticking.