During drilling, different kick locations significantly impact the formation-wellbore temperature (FWT) profile under the co-existence of kick and leakage condition (CKL). To ensure safety and efficiency during drilling, we study the effect of different kick locations on the FWT under the CKL. In this paper, a full transient heat transfer model based on the first law of thermodynamics is established to obtain four distinct WFT profiles under CKL conditions, incorporating both convective heat transfer and variable mass flow effects. Compared with the actual temperature measurement data, the reliability of the developed model is verified. The case studies show that the annular temperature (AT) is lower under the single-point leakage (SL), continuous leakage (CL), and CKL conditions than that in the normal drilling condition. Wellhead temperature in CKL differs significantly from that in normal drilling (ND). As the kick location gets closer to the bottom hole, the AT gets higher, and the temperature difference between the formation and annular gets smaller. Compared with the wellbore temperature profile under ND, the kick location can be detected by real-time monitoring of the FWT profile under the CKL.

Double-wall drill pipe reverse circulation drilling is expected to alleviate cutting-transport difficulties and the high risk of lost circulation during the shallow-section drilling of ultra-deep wells. Based on wellbore hydraulics theory and a transient solid–liquid two-phase flow model in the wellbore, considering the flow path transition effect at the reverse circulation converter near the bit, a corrected pressure loss method for the inner pipe accounting for cuttings influence is proposed, and a correlation for calculating the converter pressure loss is derived. A wellbore pressure calculation model for reverse circulation drilling using a double-wall drill pipe is then established. Furthermore, the influencing factors are investigated through sensitivity analysis, and a pump pressure selection chart is developed. Field-case calculations indicate that, under identical operating conditions, the bottomhole pressure in double-wall drill pipe reverse circulation drilling is reduced by approximately 6.31 MPa compared with conventional drilling. For shallow sections (well depth of about 1200 m) under flow rates of 20–40 L/s and drilling-fluid densities of 1200–1400 kg/m³, the maximum total circulating wellbore pressure loss, after incorporating surface flowline pressure losses, is approximately 10.91 MPa. In this case, a single pump can satisfy the circulation requirement, demonstrating the advantages of simplified equipment configuration and improved field adaptability for shallow-section operations. The proposed model and charts can provide a reference for parameter optimization and pressure-control design in double-wall drill pipe reverse circulation drilling.

During depressurization-based natural gas hydrate production, low-temperature and high-pressure wellbore conditions can induce secondary hydrate formation and deposition, risking flow channel blockage and production safety compromise. This study develops a predictive kinetic model for secondary hydrate formation and blockage in annular and mist flows, the flow patterns most susceptible to hydrate hazards. The model integrates multiphase flow, heat and mass transfer, hydrate phase change, and particle transport and deposition, coupling conservation equations with hydrate phase equilibrium and flow regime transition criteria to quantitatively predict the hydrate formation rate, deposition rate, and wall blockage severity. Validation against published experimental loop data shows that model-predicted pressure drop increases fall within 5.3% of measurements. Simulations based on a production well in the South China Sea’s Shenhu area provide quantitative predictions of three key operational controls: enlarging the tubing diameter compresses the hydrate stability zone; increasing the gas–liquid ratio suppresses hydrate formation by limiting free water; and the liquid production rate exerts stronger control over formation and deposition than the gas rate. The model serves as a practical quantitative tool for wellbore blockage risk assessment and operational decision support during hydrate trial production.