The widespread application of horizontal drilling technology has significantly enhanced the development efficiency of unconventional resources, particularly shale gas, by overcoming key technical challenges in reservoir exploitation. However, wellbore instability remains a critical challenge during shale gas horizontal drilling, as borehole wall collapse often results in the accumulation of large-sized cuttings (or blocky cuttings), increasing the risk of stuck pipe incidents. In this study, a large-scale circulating loop experimental system was developed to investigate the hydrodynamic behavior of blocky cuttings transport under the influence of multiple factors, including rate of penetration (ROP), well inclination, flow rate, drilling fluid rheology, and block size. The experimental results reveal that when ROP exceeds 15 m/h, the annular solid-phase concentration increases non-linearly. At a well inclination of 60°, the axial and radial components of gravitational force reach a dynamic equilibrium, resulting in the maximum cuttings bed height. To enhance cuttings transport efficiency and mitigate deposition, a minimum flow rate of 35 L/s and a drill pipe rotation speed of 90 rpm are required to maintain sufficient turbulence in the annulus. Drilling fluid plastic viscosity (PV) in the range of 65–75 mPa·s optimizes suspension efficiency while minimizing circulating pressure loss. Additionally, increasing fluid density enhances the transport efficiency of large blocky cuttings. A drill pipe rotation speed of 80 rpm is recommended to prevent the formation of sand-wave-like cuttings beds. These findings provide valuable hydrodynamic insights and practical guidelines for optimizing hole-cleaning strategies, ensuring safer and more efficient drilling operations in shale gas horizontal wells.

The application of the hole cleaning device in downhole is a new technology that can improve the problem of cuttings accumulation in the annulus and improve the hole cleaning effect of the wellbore during drilling. In this paper, the Reynolds Averaged Navier–Stokes model, together with the Realizable k-ε turbulence model, are used to perform transient simulations. The effects of rotational speed, blade shape, and helical angle on the initial swirl intensity and its decay behavior along the flow direction are studied. The swirl number, the initial swirl intensity, the decay rate, the tangential velocity distribution, and the variation of pressure are analyzed. The results indicate that the swirl number of the swirl flow exponentially decays along the flow direction. The straight blade and V-shaped blade have different swirl flow induction mechanisms. Under specific drilling parameters, the critical helical angle is determined for both types of blades. When the selection of the helical angle is close to the critical value, the swirl flow will be close to the axial flow, which is of little help in hole cleaning. Moreover, the rotation direction of swirl flow will change when the helical angle exceeds the critical value.

Various kinds of drilling string vibration behaviors exist while deviated well (crooked hole) is drilling; the serious drilling string axial vibration will cause bit jumping, which is one of the most factors influencing deviated well drilling. Serious bit jumping phenomenon indicates that drilling string axial vibration shouldn't be neglected. This research studies on the whole drilling string in the crooked hole as subjects, and analyzes the laws that the whole drilling string axial dynamic behavior followed under the condition periodic exciting force exists. Through the whole and the part drilling string finite element analysis, mass matrix, stiffness matrix and dynamic matrix equation are acquired. Using computer program, distribution laws of drilling string axial vibration frequency are acquired, which indicates bit jumping occurs when forced vibration frequency and natural frequency are closed to each other. This paper provides a theoretical basis of researching drilling string dynamic behavior in the crooked hole, and the obtained observation would be a further guidance for analyzing drilling string vibration on extended reach well drilling.

Reliable wellbore cleaning remains difficult in deviated, horizontal, extended-reach, deep, and ultra-deep wells because the downhole distribution and mechanical state of cuttings beds cannot usually be observed directly. This review examines cuttings-bed dynamics, multiscale modeling, compressible multiphase constraints, and field-validation pathways for drill cuttings transport and wellbore cleaning. Bibliometric mapping of 625 Web of Science records was combined with critical assessment of 204 technically screened studies and 56 engineering-oriented OnePetro records. Bed height, cuttings concentration, pressure response, equivalent circulating density/bottomhole-pressure (ECD/BHP) margin, solids residence time, and packoff tendency are identified as bridge variables linking particle-scale behavior with operational risk. Recent studies strengthen wet-bed erosion and friction characterization, non-spherical and geometry-resolved CFD–DEM, hybrid prediction, compressible pressure–solids coupling, and field observability. Study-level comparison shows that ML approaches differ markedly in data provenance, validation design, physical integration, uncertainty reporting, and transfer evidence. An uncertainty-aware, field-calibratable workflow is proposed that links synchronized measurements, complementary models, latent-state estimates with prediction intervals, section-specific probabilistic thresholds, operational response, and post-action verification. Quantitative benchmark criteria are defined for particle realism, wet-bed mechanics, tool-induced flow, compressible transport, transient field models, and advisory outputs.

This paper investigates the impact of temperature on the rheological behavior of cement slurry and drilling fluid and examines how various factors, such as displacement speed, casing centralization, and density difference, influence displacement efficiency during cementing operations. Using numerical simulations validated against experimental data, we explore how these factors interact under different temperature conditions. Results indicate that temperature changes significantly affect the flow characteristics, displacement interface stability, and overall displacement efficiency. Findings demonstrate that optimizing these parameters according to temperature conditions can significantly enhance cementing performance and reduce the risk of fluid channeling and instability.

Exploitation of deep (>4000 m) tight geothermal reservoirs is constrained by low native permeability and premature thermal breakthrough, limiting sustainable heat recovery. Here, we investigate THM (thermo–hydro–mechanical) controls on fluid flow and heat transport during cold-water reinjection in deep tight sandstone reservoirs through an integrated framework linking two-dimensional mechanistic analysis with three-dimensional field-scale modeling. A two-dimensional thermo-poroelastic model reveals that strong thermal contrasts induced by cold-fluid injection cause contraction of the rock framework and transient pore-space dilation under confinement, producing short-term permeability enhancement. This process alters local flow capacity and redirects early cold-front migration, with persistent impacts on subsequent heat transport. Field-scale simulations further quantify the coupled effects of well spacing and reinjection temperature on thermal breakthrough, defined as a 1 °C decline in production-well temperature. Increased well spacing delays cold-front arrival and significantly retards breakthrough, whereas lower reinjection temperature enhances early heat extraction but accelerates convective transport, leading to earlier breakthrough. The combination of thermally enhanced permeability and intensified convection promotes preferential flow channels, increasing breakthrough risk. Balancing thermal-breakthrough delay against the heat-extraction driving force, the simulations delineate a favorable engineering window for the investigated conditions and clarify how cooling-sensitive permeability evolution affects preferential flow and reservoir-scale thermal response.