Abstract:As drilling depths extend to the 10000-meter level and beyond， factors such as high temperature， high pressure， high in-situ stress， ultra-long drill strings， and long-period continuous operations are coupled. The principal challenge facing ultra-deep continental drilling equipment has shifted from improving individual equipment performance indicators， such as load capacity and power， to the synergistic enhancement of comprehensive operational capability and system reliability under complex and extreme working conditions. From the perspective of equipment system evolution， this paper analyzes the development requirements of ultra-deep continental drilling equipment and systematically reviews the state-of-the-art of key technologies， including automated drilling rigs， pipe handling and storage， energy saving and storage， and intelligent safety operation and maintenance， while also addressing the special requirements of high-quality coring equipment for scientific drilling. Currently， ultra-deep continental drilling equipment has gradually evolved from stand-alone performance enhancement， such as high load and high torque， toward automation， complete-set configuration， and intelligence. However， for drilling at 10000 m and beyond， prominent problems remain， including insufficient multi-equipment collaboration capability， weak capability for continuous handling and condition monitoring of ultra-long drill strings， and inadequate dynamic energy optimization. Looking ahead， ultra-deep continental drilling equipment should shift from "stand-alone capability improvement" to "system capability reconstruction." Targeting full-process efficient， safe， continuous， and low-consumption operations， priority should be given to developing high-efficiency drilling equipment systems centered on "one-button" multi-equipment collaborative control， software-hardware modular integration， automation-intelligence fusion， and downhole autonomous driving technology. This will promote the evolution of ultra-deep continental drilling from "surface-equipment-dominated， stepwise operation" to "surface-downhole collaboration， full-process closed-loop control， and autonomous continuous operation，" providing a reference for the system construction and key-technology breakthroughs of future ultra-deep continental drilling equipment.

Abstract:To address the challenge posed by the lack of domestically manufactured wireline coring equipment for ultra-deep scientific drilling exceeding 10000 m in China， a design study on a 13000 m deep wireline coring winch was conducted. Considering complex working conditions such as the piston effect induced by narrow annular clearance and caused by borehole deviation friction， a mechanical model for wire rope hoisting was established. Numerical simulation was performed to quantify the peak load of the wire rope under different accelerations， determining a safe operating range with a starting acceleration of 0.1 m/s2 and a maximum constant hoisting speed of 1 m/s. Accordingly， the core technical parameters were determined， including a rated traction force of 200 kN， a rope storage capacity of no less than 14500 m， a wire rope diameter of 17.3 mm， and a wire rope grade of 2160 MPa. An integrated structure combining a tension-reducing traction winch and a storage winch was proposed. A master-slave synchronous drive system with dual friction drums was designed， incorporating a slack compensator， PID-based constant tension control， and automatic spooling technology to achieve orderly winding and tension buffering of the wire rope. A distributed electrical control system based on the Profinet bus was developed to ensure precise operation. The results indicate that the proposed design can effectively reduce the winding tension of the wire rope， mitigate issues of disorderly spooling and associated wear， and improve control accuracy， thereby meeting the requirements for safe and continuous coring in ultra-deep wells. This study provides key technical support for the localization of deep earth exploration equipment in China.

Abstract:To address the critical challenges in extra-deep drilling beyond 10000 meters， such as downhole tool failures and drilling fluid performance degradation caused by extreme high temperatures， this study investigates the efficacy of surface cooling of drilling fluid. A numerical model of wellbore-formation coupled heat transfer was established and validated against measured data from Well Yaha 501. Using the bottom-hole circulating temperature， maximum drilling fluid temperature， and return drilling fluid temperature as key evaluation metrics， simulation analysis was conducted to examine the temperature control performance of surface cooling at designed depths of 8000 m， 11000 m， and 13000 m. The results demonstrate that implementing surface cooling reduced the bottom-hole circulating temperature and maximum drilling fluid temperature by 24.3 ℃ & 24.4 ℃， 17.4 ℃ & 17.9 ℃， and 12.0 ℃ & 12.5 ℃， respectively. Without cooling， the return drilling fluid temperature after four circulation cycles reached 92.3 ℃， 96.2 ℃， and 94.3 ℃. In contrast， with surface cooling， it stabilized at approximately 60 ℃. This study provides a theoretical basis and quantitative guidance for wellbore temperature control and safe operations in extra-deep drilling.

Abstract:Ultra-high formation temperature poses a core challenge for extra-deep scientific drilling. To address the bottleneck where existing single cooling technologies fail to meet the temperature control requirements of a 13000 m wellbore， this study employs numerical simulation to evaluate the cooling performance of a combined approach integrating surface drilling fluid cooling and insulated drill pipe， with bottom-hole circulating temperature， maximum wellbore drilling fluid temperature， and return drilling fluid temperature as evaluation indices. The results indicate that applying the combined technology from 11000 to 13000 m can control the bottom-hole circulating temperature， maximum wellbore drilling fluid temperature， and outlet drilling fluid temperature at 285 ℃， 291 ℃， and 63 ℃， respectively. Increasing the application length of insulated drill pipes can effectively reduce wellbore drilling fluid temperatures， and for every 0.1 ℃/100 m decrease in geothermal gradient， the bottom-hole circulating temperature and maximum wellbore drilling fluid temperature both decrease by 9 ℃. This research demonstrates that the combined technology can control key temperature parameters within a safe range for extra-deep drilling operations， providing a crucial theoretical basis for drilling engineering design and site selection， and offering technical support for the successful implementation of extra-deep scientific drilling projects.

Abstract:In deep oil， gas， and geothermal drilling， elevated bottom-hole temperatures degrade drilling fluid performance， posing a severe threat to operational safety and efficiency. As the core equipment of the drilling fluid cooling system， the plate heat exchanger （PHE） has internal flow and heat transfer characteristics that critically determine overall system performance. In this study， a high-temperature-resistant water-based drilling fluid was investigated via conjugate heat transfer numerical simulations using ANSYS Fluent， with model validation performed with laboratory cooling experiments. The evolution of flow field non-uniformity， pressure drop， Nusselt number （Nu）， thermal resistance distribution， and comprehensive performance index was systematically analyzed over a wide Reynolds number range （17≤Re_m<1700）. The results demonstrate that flow separation induced as the drilling fluid flows past plate contact points generates low-velocity vortex zones， which are identified as high-risk regions for fouling deposition. Both flow field non-uniformity and pressure drop exhibit piecewise nonlinear variations with increasing Re_m， clearly delineating the transition from laminar to turbulent flow， with Re_m=50 identified as the laminar-to-transitional critical threshold. As Re_m increases， Nu increases substantially， yet its growth rate declines through four distinct stages. The dominant thermal resistance shifts from the drilling fluid side to the water side when Re_m>560. The comprehensive performance index decreases continuously with increasing Re_m， indicating that the heat transfer gain per unit increase in flow velocity grows more slowly than the accompanying rise in flow resistance， leading to sustained degradation in overall energy efficiency. This study elucidates the trade-off mechanism between heat transfer enhancement and flow resistance for high-viscosity drilling fluids， providing theoretical support for the optimal design and operational regulation of high-temperature drilling fluid cooling systems.

Abstract:To address the issues of poor real-time performance and insufficient accuracy in traditional manual measurement of drilling fluid rheological parameters， this study developed a six-speed online drilling fluid measurement system. By deriving the shear rate based on the concentric cylinder flow model， parameter solutions were achieved by incorporating the Bingham model， power-law model， and Herschel-Bulkley rheological model. The end effect was analyzed through CFD numerical simulation， and a corresponding dynamic correction method was proposed. An experimental platform was established to compare the measurement results of the online module with those of a standard Fann 35 viscometer. The test results show that the system exhibits high consistency with the benchtop viscometer， with an average deviation of less than 5% between the readings. The fitting error of the HB model is below 2%， significantly outperforming the Bingham model. Temperature reduction markedly increases plastic viscosity and yield stress， enabling data standardization through temperature compensation. The system responds to step changes in rotational speed within approximately 2 s， demonstrating excellent dynamic performance. This system enables real-time， continuous， and high-precision measurement of rheological parameters， providing effective technical support for intelligent monitoring of drilling fluid performance and safe， efficient drilling operations.

Abstract:The operating environment for deep drilling is extreme， where critical components are prone to issues such as wear， fatigue， and seal failure. Traditional operation and maintenance （O&M） models， primarily based on scheduled maintenance and reactive repair， struggle to meet the requirements for continuous operation and operational safety. Addressing the intelligent O&M requirements for deep drilling equipment， this paper systematically analyzes key requirements including user roles， system deployment， data acquisition and transmission， application scenarios， and functional configuration. It proposes a technical scheme for multi-source heterogeneous data integration and transmission， establishing an integrated approach that coordinates WITSML/ETP， OPC UA， and Kafka. A distributed and elastic "cloud-edge-device" collaborative architecture is constructed， introducing K3s and KubeEdge for edge service deployment and cloud-edge collaboration， while employing time-series databases and graph databases for data and knowledge management. Based on this， a prototype software for the intelligent O&M system is developed， integrating functions such as digital twin， real-time monitoring， and early fault warning. The applicability of the system under engineering conditions is validated using steel wire rope electromagnetic inspection as a case study. This research provides an implementable technical architecture and pathway for intelligent O&M of deep drilling equipment， offering engineering reference value for enhancing equipment operational reliability and O&M efficiency under extreme conditions.

Abstract:To address the urgent demand for an 80 MPa ultra-high-pressure drilling pump in 15000 m ultra-deep well drilling， and to overcome the bottleneck that existing digital twins lack mechanical data under extreme operating conditions， a systematic mechanical performance analysis was conducted on the crosshead， a key component of the ultra-high-pressure drilling pump. First， based on hydraulics theory， the rated pump pressures and displacements under different liner diameters （110~180 mm） were calculated， and a kinematic and force model of the crosshead was established to define its load boundary conditions. Subsequently， based on the Hertz contact theory， finite-element static simulations were performed using COMSOL software under various combinations of liner diameter and pump pressure. The results indicate that the maximum stress on the crosshead is positively correlated with both liner diameter and pump pressure， and the effect of liner diameter variation on stress is significantly greater than that of pump pressure. The stress concentration zone is located at the transition fillet between the outer edge of the pin hole and the lug body. Under the rated-pressure and maximum-displacement conditions， the maximum stresses are 133.3 MPa and 142.8 MPa， respectively， both far below the material''s yield strength of 860 MPa. This study quantifies the stress-response surface under coupled liner-diameter-pump-pressure operating conditions， fills the gap in mechanical data for the power end of ultra-high-pressure pumps for ultra-deep wells under extreme conditions， and provides a theoretical basis for on-site cylinder liner replacement strategies and fatigue-life prediction of crossheads.

Abstract:To elucidate the elevated-temperature fatigue failure behavior of lightweight aluminum alloy drill pipe materials in deep drilling， axial tension-compression stress-controlled fatigue tests were conducted on 2024-T3 aluminum alloy at 120， 160， and 200 °C with stress amplitudes of 200， 250， and 300 MPa. The failure mechanisms were analyzed via stress-strain hysteretic response， scanning electron microscopy fracture morphology， and backscattered electron imaging. The results show that fatigue life decreases markedly with increasing stress amplitude， which is the primary factor controlling life attenuation. The influence of temperature exhibits significant stress amplitude dependence； at intermediate and low stress amplitudes of 200 and 250 MPa， the fatigue life at 200 °C shows a recovery compared with that at 160 °C， whereas at a high stress amplitude of 300 MPa， it declines continuously with rising temperature. Analysis of the hysteretic response reveals that cyclic plastic deformation is enhanced at 160 °C， resulting in increased macroscopic inelastic energy dissipation. However， at 200 °C， the hysteresis loop area does not expand continuously， indicating a discrepancy between macroscopic dissipated energy and local fatigue damage， with the dominant failure mechanism shifting from uniform plastic dissipation to localized strain concentration and particle-matrix interface damage. Observations of fracture morphology indicate that crack propagation is dominated by stable fatigue striations at low temperatures and low stress amplitudes. Elevated temperatures and high stress amplitudes lead to rougher fracture surfaces with increased secondary cracks， dimples， tear ridges， and particle pull-out features. Backscattered electron imaging confirms that Cu-enriched coarse second-phase particles serve as critical microscopic damage sources for crack initiation and propagation. It is concluded that the fatigue failure is jointly governed by matrix thermal softening， cyclic plastic deformation， and particle-matrix interface damage. Under high-temperature and high-stress-amplitude conditions， interface decohesion and microvoid coalescence accelerate crack propagation and reduce fatigue life. The findings provide experimental support and a theoretical basis for service reliability evaluation of lightweight aluminum alloy drill pipe in ultra-deep wells.

Abstract:To address the significant propagation time lag of pressure disturbances in long wellbores during deep drilling and the inadequacy of steady-state hydraulic models in accurately characterizing bottomhole transient fluctuations under narrow density windows—which may readily induce well control risks—a one-dimensional transient hydraulic model for the wellbore was established. Taking absolute pressure and volumetric flow rate as primary variables， the model couples the Tait high-pressure equation of state， the Korteweg system wave speed correction， and non-Newtonian fluid rheology with pressure-viscosity enhancement， thereby constructing a state-dependent closure system for frictional dissipation along the wellbore. The governing equations are solved in the time domain using the method of characteristics that satisfies the CFL stability condition. Steady-state benchmarking and propagation time lag verification show that the maximum deviation of the steady-state equivalent circulating density is 0.64%， and the relative error of the dynamic time lag is less than 0.01%. On this basis， continuous field validation was conducted by utilizing dynamic mud logging pump rate sequences from a deep well with a static pressure up to 20 MPa. The predicted standpipe pressure was controlled within ±1.5 MPa of field measurements， confirming the model''s physical accuracy under strongly time-varying boundary conditions. Further analysis indicates that bottomhole pressure fluctuations share the same dominant frequency as the wellhead input， yet exhibit a distinct time lag and amplitude attenuation. The propagation time lag increases approximately linearly with well depth， whereas the peak-to-peak amplitude of bottomhole pressure fluctuations exhibits non-monotonic variation. The amplitude-frequency characteristics of the transfer function reveal that this phenomenon originates from the combined modulation of standing wave interference and frequency-domain resonance in the long wellbore； at specific depths， the in-phase superposition of incident and reflected waves leads to anomalous pressure amplification. The proposed model effectively reveals the propagation process of pressure disturbances and the dynamic response characteristics at the bottomhole in long wellbores， providing a theoretical basis and computational tool for hazardous frequency avoidance and dynamic pressure early warning in managed pressure drilling under narrow density windows.

Abstract:To address the strength degradation of slope rock masses in cold regions under freeze-thaw action， the bluish-grey sandstone from the Yulong Copper Mine slope was taken as the research object. Through indoor freeze-thaw cycles， SHPB dynamic impact tests， and nuclear magnetic resonance （NMR） pore analysis， the dynamic mechanical degradation laws， energy evolution characteristics， and pore structure evolution laws of semi-saturated sandstone under freeze-thaw action were systematically investigated， and a freeze-thaw strength degradation model based on absorbed energy was established. The results show that as the number of freeze-thaw cycles increases， the dynamic peak stress of sandstone decreases from 65.45 MPa to 51.8 MPa， exhibiting a nonlinear degradation trend of rapid initial decline followed by slow attenuation. The dynamic stress-strain curve sequentially undergoes an elastic stage， a strain-softening stage， and a rapid unloading stage. The strain-softening stage gradually shortens with increasing freeze-thaw cycles， accompanied by the phenomena of stress drop and strain rebound. Both incident energy and transmitted energy generally show a decreasing trend with increasing freeze-thaw cycles， whereas the reflected energy increases significantly at 20 freeze-thaw cycles. High freeze-thaw cycles promote the migration of moisture into larger pores， expand the pore distribution range， and enhance the response characteristics of mesopores and macropores. The research findings reveal the damage evolution mechanism of semi-saturated sandstone under freeze-thaw cycles， providing a theoretical basis for the stability evaluation and protection design of slope engineering in cold regions.

Abstract:Under complex conditions， PDC bits are prone to abnormal failures such as cutter breakage， delamination， and fragmentation due to frequent impact vibration. Adopting a backup cutter layout is an effective method to reduce impact loads and improve the load environment. Based on the formation characteristics of the Longmaxi Formation shale in southern Sichuan， a finite element simulation model of the "main cutter-backup cutter" combined cutting was established using Abaqus software and verified by experiments. The effects of backup cutter shape， exposure height difference， and cutting depth on the working load of the main cutter were systematically analyzed. The results show that a reasonable backup cutter layout can effectively share the impact load on the main cutter and reduce stress concentration. The spherical cutter exhibits the best overall stress dispersion effect and the widest applicability， while the truncated cone cutter achieves the highest load-sharing efficiency at an exposure height difference of 0.5 mm and a cutting depth of 1.0 mm. An exposure height difference of 0.5 mm yields the best comprehensive load reduction， but it should be avoided when the cutting depth is 1.0 mm. Without backup cutters， stress concentration is most severe at a cutting depth of 1.0 mm； when matched with appropriate backup cutters， cutting depths of 0.5 and 1.5 mm are recommended. The slope angle of the conical cutter has no absolute superiority or inferiority， requiring coupled matching with the cutting depth and exposure height difference. For drilling in the southern Sichuan shale formation， the spherical cutter is recommended as the backup cutter， with the exposure height difference set to 0.5 mm and the cutting depth controlled at 0.5 or 1.5 mm. The results of this study can provide theoretical support and technical references for the optimized design of customized PDC bits in complex formations.

Abstract:With the accelerating consumption of mineral resources and the introduction of the national new round of mineral prospecting breakthrouch strategy， new requirements have been put forward for exploration and prospecting in complex deep overburden layer， where the geological drilling environment is complex. Wire-line core drilling technology is widely used for drilling in the complex strata. To enhance the drilling efficiency and core recovery of wire-line coring drilling in deep overburden layers， and to maintain borehole wall stability， an environmentally friendly plant-gum film-forming drilling fluid system was developed. Through optimization tests， konjac gum was selected as the film-forming matrix. On this basis， the film-forming aid PVA， the rheology modifier HJ， and polyamine anti-sloughing inhibitor AB-1 were further identified. Based on the response surface test， the optimized formulation K-PA of the plant-based film-forming drilling fluid was obtained， that is 0.3% konjac gum + 0.9% PVA + 0.6% HJ + 1% AB-1 + 0.2% soda ash， moreover， its film-forming and anti-sloughing mechanism was analyzed. This drilling fluid system exhibits outstanding film-forming filtration reduction and hydration inhibition capabilities to achieve anti-sloughing and wall protection， showing good adaptability to deep overburden layers. The performance test results are highly consistent with the model predictions， demonstrating the high reliability of the response surface test design. The research results provide a new approach for solving complex formation problems， and also offer certain reference significance for the development of new environmentally friendly solid-free drilling fluids.

Abstract:To address the drilling challenges of insufficient thermal stability and salt resistance as well as high costs of treatment agents in deep coal measure strata， a brine drilling fluid base slurry was prepared using bentonite， NaCl， Na?CO?， and NaOH as raw materials. HCalvis-5， HCalvis-4， S092， cationic starch， and HE-150-were selected to investigate the effects of additive type and concentration on the rheological properties and fluid loss of the drilling fluid. The overall system performance was optimized by compounding antioxidants of different types and dosages， and the optimal formulation was determined. Fourier transform infrared spectroscopy （FT-IR） and Zeta potential analysis were employed to elucidate the synergistic mechanism of the treatment agents. The results indicate that the optimal formulation is "base slurry + 2.0% HCalvis-5 + 1.0% Na?SO?，" with an optimal application temperature of 120 °C. After hot rolling at 120 °C for 16 h， the drilling fluid exhibited an apparent viscosity of 27 mPa·s and an API filtrate loss of only 8.0 mL. The 24 h linear swelling ratio of bentonite was merely 1.67%， and the high-temperature rolling recovery rate reached 58.64%， demonstrating excellent high-temperature resistance， hydration inhibition， and filtration control. Microscopic mechanism analysis reveals that HCalvis-5 adsorbs onto and encapsulates clay particles via hydrogen bonding， forming a dense filter cake， while Na?SO? scavenges high-temperature free radicals to suppress oxidative degradation of polymers. The synergistic action of the two components ensures the high-temperature stability of the system. Featuring low raw material costs and a simple preparation process， this formulation can effectively meet the engineering requirements for drilling in deep coal measure strata， thereby providing experimental evidence and theoretical support for further optimization and upgrading of drilling fluid systems for higher-temperature ultradeep formations.

Abstract:As a commonly used vertical protection method， the cut-off wall is highly favored in the hydropower construction industry. However， during the trenching construction of cut-off walls in coarse-grained soil strata， because of strong permeahility， serious leakage of wall-fixing slurry often occurs， leading to difficulties in film-forming and frequent trench wall collapse accidents. Therefore， to improve the stability of trench walls caused by slurry permeation， the base fluid was optimized by selecting suitable clay， pH modifiers， and rheological modifiers. Subsequently， a self-designed slurry permeation experiment apparatus was used to select coarse sand as the coarse-grained material， forming a wall-fixing slurry system for cut-off walls in coarse-grained strata. The effects of coarse sand particle size and dosage on the slurry''s permeation and film-forming characteristics were also analyzed. The study concluded that the slurry system for trenching in coarse-grained strata consists of clean water+4% clay+4% sodium bentonite+0.2% 3.4-modulus sodium silicate+0.18% sodium carboxymethyl cellulose+2.5% 0.154 mm sand particles. The film-forming speed and quality of sand-added slurry in coarse-grained strata primarily depend on the particle size and dosage of coarse sand. As the particle size and dosage of coarse sand increase， the film-forming speed of the slurry accelerates， whereas the film-forming quality decreases with the increasing sand dosage. The permeation and film-forming mechanism of sand-added slurry involves three synergistic effects： the preliminary improvement of the coarse-grained stratum by sand particles， the stable clogging of the permeation zone within the stratum， and the filtration and film-forming of mud cake on the stratum surface. These combined actions reduce slurry leakage and maintain the stability of the excavation face in coarse-grained strata. The research findings provide guidance for optimizing the formulation of engineering wall-fixing slurry in coarse-grained strata and offer valuable references for similar engineering projects.

Abstract:Small-diameter core drilling plays an irreplaceable role in deep mineral resource exploration and marine geological surveys， however， wellbore stability control， harmful gas prevention， and full core quality assurance under complex marine environments and diverse strata conditions have long been technical bottlenecks in the industry. To address the engineering challenges such as difficult core preservation in unconsolidated soft plastic strata， easy core abrasion in hard strata， low core recovery in fractured coal-bearing strata， and deep hydrogen sulfide abnormal overflow in the CSDP-2 well （China Eastern Sea Area Scientific Drilling Well）， this paper systematically conducted research on improvements of the blowout preventer-assisted wire-line coring technology. By optimizing the drilling speed control strategy and establishing a pressure balance system for drilling fluid reinjection， the issues of wellbore collapse caused by tripping operations in shrinkage-prone strata and negative pressure suction during wire-line coring were resolved. Relying on the blowout preventer kill mainfold， a reverse circulation drilling fluid system was constructed， achieving multiple objectives including wellbore stability maintenance， harmful gas containment， and solid phase precipitation prevention. Combined with the adaptability modification of the "Tanhai 1" platform， a full coring technology system for complex shallow sea environments was formed. The improved technology achieved a 97.68% average core recovery rate across the entire 2843.18 m well section of the CSDP-2 well， setting a global record for full core recovery in continental shelf scientific drilling. The hydrogen sulfide overflow concentration was controlled below 0.5×10^-6， ensuring zero-accident safe construction. The engineering cost was significantly lower than conventional offshore oil and gas drilling， filling the gap in low-cost， high-efficiency drilling technology for domestic continental shelves. Combined with the industry development trend， the technology application prospects are discussed from the aspects of equipment integration， intelligent control， multi-scenario adaptation， etc. It provides a new technology scheme for the small-diameter deep hole drilling in complex strata and the ocean.

Abstract:Various typical karst problems， including karst fissure zones， bead-like small karst caves， and large karst caverns are encountered in a core drilling project deployed in the periphery of a mining area in Southwest Guangxi. Complex downhole conditions exist such as lost circulation， unstable borehole walls， and pipe string buckling. Field construction was successfully completed by implementing corresponding drilling techniques alongside plugging measures， that is optimizing the borehole structure in complex karst formations to maintain borehole wall stability， adopting drilling with lost circulation technology when drilling across bead-like small cave formations， conducting feasibility analysis of pipe string bending in large caverns， adopting corresponding technical measures to reduce string bending， and using material-feeding plugging methods to re-establish circulation. By systematically reviewing the multiple complex situations encountered during core drilling in the Southwest Guangxi region， corresponding technical countermeasures have been summarized， aiming to provide references for similar core drilling projects.

Abstract:To address the technical problem of low construction efficiency of geothermal directional wells in the Dongli Block of Tianjin， customized research and development of high-efficiency PDC drill bits was carried out targeting the formation characteristics of this block. By optimizing the drill bit profile structure and tooth arrangement density， combined with simulation analysis and laboratory tests， the rock-breaking force characteristics and stress distribution laws of triangular prism cutter and plane cutter were compared， as a result， the triangular prism cutter were selected as the main cutters. A composite processing technology integrating UG-CAM five-axis machining and plasma automatic welding was adopted to ensure the machining accuracy and wear resistance of the drill bit. Field application data show that the newly developed PDC bit achieved a total footage of 460.58m in the DL-93 geothermal directional well， with an average rate of penetration （ROP） of 3.68m/h， which is 41% higher than that of the conventional PDC drill bits in adjacent wells， meeting the requirements for efficient drilling of geothermal directional wells in this area.

Abstract:After long-term waterflooding and polymer injection development， the mature oilfield are subjected to the complex working conditions including coexisting multi-pressure systems， interleaved oil and water layers， polymer contamination and active formation water invasion， as a result， the integrity of the cement sheath and the long-term inter-zonal sealing performance were insufficient， and the oil wells cannot be put into production directly， or inter-zonal channeling frequently occurs after production， which severely restricts the fine exploration of remaining oil potential and long-term stable production in mature oilfields. In view of this， firstly， experiments and mechanism analysis are carried out on formation water invasion， polymer contamination， residual false mud cake， and displacement channeling to identify the main controlling factors and propose key technical countermeasures for long-term anti-channeling cementing. Nano-silicon fluid and thixotropic agent were selected， anti-channeling parameters were optimized， and an efficient water anti-channeling cement slurry system was developed. Based on the synergistic mechanism of permeation swelling and mechanical erosion， a dual-effect composite flushing fluid was developed. The effective anti-channeling annular pressure difference standard was determined to be 3~7 MPa， and an adjustable density heavyweight spacer fluid was developed， a pressure compensation method was designed， and a full-process pressure stabilization and anti-channeling technology was established. Supporting measures such as efficient mud cake removal and enhanced centralization of key layers were implemented to form a long-term anti-channeling cementing technology for complex formations. The results show that the high-quality rate of cementing for the first and second interfaces in an eastern mature oilfield has been significantly improved. The cementing qualification rate for thin interlayers and water-flooded zones has increased from less than 60% to 100%， and the oil well production rate has increased from 85% to 100%. This effectively solves the problem of insufficient long-term sealing of the cement sheath in mature oilfield areas， providing technical support for the layered subdivision development of similar mature oilfields.