Lost circulation in fractured formations remains a persistent challenge in drilling operations, causing substantial economic losses and increased operational risk. Conventional granular bridging packs are mechanically fragile and can be destabilized by pressure fluctuations, limiting one-trip plugging efficiency. This study incorporates a thermosensitive adhesive resin into bridging assemblies to enhance plug integrity by promoting interparticle adhesion and particle-wall coupling after thermal activation. Oscillatory temperature-sweep rheometry is used to quantify the temperature-dependent viscoelastic response of resin-particle composites. A wedge-shaped fracture analogue with photoelastic visualization is used to monitor force chain development and uniformity during progressive loading. Discrete element method simulations in Particle Flow Code, using a linear parallel-bond contact model, resolve mesoscale load-transfer pathways and isolate the contribution of adhesive interactions. Results indicate that thermosensitive adhesive resin increases assembly coherence, promotes a stable load-bearing skeleton, and suppresses stress localization that typically precedes plugging failure. The strengthening trend is governed by particle rigidity and surface characteristics, yielding consistent load-transfer patterns across experiments and simulations. These findings demonstrate that thermally activated adhesion can transform unconsolidated granular packs into mechanically stable plugging zones, providing a mechanistic basis for designing high-stability lost circulation control systems in fractured formations.

Lost circulation, the significant penetration of drilling fluid into formations during drilling, leads to excessive fluid consumption, non-productive time, and potential well control incidents. This study developed a tunable polymer gel system for plugging lost circulation zones of various scales. Its mechanical properties can be controlled by adjusting the concentration, temperature, gelling time, and aging time. At 120 ℃ and 10 h gelling time, increasing concentration from 12% to 20% steadily enhanced mechanical properties: storage modulus rose from 750 to 3171 Pa, and tensile stress increased from 20.03 to 67.8 kPa. However, under different temperature and time regimes, the mechanical properties of polymer gels first strengthened and then weakened or showed a trend of strengthening, weakening, and then strengthening again. For example, under gelling temperature 120 ℃ and 14% concentration, when the gelling time was increased from 4 to 10 h, the tensile stress of polymer gel increased from 4.103 to 30.07 kPa, but when the gelling time was further extended from 10 to 12 h, the tensile stress was reduced from 30.07 to 11.33 kPa. With further extension of time to 14 h, the tensile stress increased again to 43.91 kPa. Comprehensive microstructural analysis revealed how these factors influence gel properties. Subsequently, the simulated plugging experiments of fractures and sand-filled pipes were conducted using the polymer gel with a concentration of 14% and a temperature of 140 ℃ for 8 h, and the plugging strength was 5.8 MPa for the parallel fracture of 5 mm, and 10.06 MPa for the sand-filled pipe with a 3 mm fracture and an inner diameter of 3 cm in the outlet pipe, which indicated that the polymer gel system exhibited strong pressure-bearing plugging ability for both the fracture and the fracture/vuggy. The proposed polymer gel was applied in the field of HD29-H8 well in the Tarim Basin of Xinjiang, China, and successfully plugged the loss formation above 5000 m, which demonstrated that it can effectively plug high-temperature and high-pressure reservoirs.

Lost circulation, a recurring peril during drilling operations, entails substantial loss of drilling fluid and dire consequences upon its infiltration into the formation. As drilling depth escalates, the formation temperature and pressure intensify, imposing exacting demands on plug materials. In this study, a kind of controllable curing resin with dense cross-network structure was prepared by the method of solution stepwise ring-opening polymerization. The resin plugging material investigated in this study is a continuous phase material that offers effortless injection, robust filling capabilities, exceptional retention, and underground curing or crosslinking with high strength. Its versatility is not constrained by fracture-cavity lose channels, making it suitable for fulfilling the essential needs of various fracture-cavity combinations when plugging fracture-cavity carbonate rocks. Notably, the curing duration can be fine-tuned within the span of 3–7 h, catering to the plugging of drilling fluid losing of diverse fracture dimensions. Experimental scrutiny encompassed the rheological properties and curing behavior of the resin plugging system, unraveling the intricacies of the curing process and establishing a cogent kinetic model. The experimental results show that the urea-formaldehyde resin plugging material has a tight chain or network structure. When the concentration of the urea-formaldehyde resin plugging system solution remains below 30%, the viscosity clocks in at a meager 10 mPa·s. Optimum curing transpires at 60 ℃, showcasing impressive resilience to saline conditions. Remarkably, when immersed in a composite saltwater environment containing 50000 mg/L NaCl and 100000 mg/L CaCl₂, the urea-formaldehyde resin consolidates into an even more compact network structure, culminating in an outstanding compressive strength of 41.5 MPa. Through resolving the correlation between conversion and the apparent activation energy of the non-isothermal DSC curing reaction parameters, the study attests to the fulfillment of the kinetic equation for the urea-formaldehyde resin plugging system. This discerning analysis illuminates the nuanced shifts in the microscopic reaction mechanism of the urea-formaldehyde resin plugging system. Furthermore, the pressure bearing plugging capacity of the resin plugging system for fractures of different sizes is also studied. It is found that the resin plugging system can effectively resident in parallel and wedge-shaped fractures of different sizes, and form high-strength consolidation under certain temperature conditions. The maximum plugging pressure of resin plugging system for parallel fractures with outlet size 3 mm can reach 9.92 MPa, and the maximum plugging pressure for wedge-shaped fractures with outlet size 5 mm can reach 9.90 MPa. Consequently, the exploration and application of urea-formaldehyde resin plugging material precipitate a paradigm shift, proffering novel concepts and methodologies in resolving the practical quandaries afflicting drilling fluid plugging.