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Abstract:Different substances， such as formation particles， microorganisms and injections， will cause blockage of oil and gas wells in the process of migration and retention along with pipeline fluid and solid. This paper divides the blockage areas into four categories： blockage of surface collection and transmission pipelines， blockage of wellbore， blockage of sand control media and blockage of formation pores. The physical， chemical and biological factors causing plugging and plugging characteristics are analyzed in this paper. The present status of plugging removal technology commonly used in the process of offshore oil and gas resource development is summarized， and the plugging removal technology is divided into four categories， namely physical， chemical， biological and composite. At the same time， it is considered that the composite plugging removal technology is the most likely to be applied to hydrate development in the future， which provides a reference for the plugging removal technology in the future development of marine natural gas hydrate resources.

Abstract:In view of the problem that the impregnated diamond bit teeth are independent of each other， and the bit is easy to slip and the individual tooth of the bit is easy to fail due to excessive force in drilling hard rocks， the bionic claw toe structure theory and the self-compensating concept are introduced to develop a bionic self-compensating integrated high-matrix impregnated diamond coring bit. In the integral cutting tooth design of the drill bit， reinforcement ribs are placed between individual teeth and also between individual tooth units to strengthen the strength of individual teeth， and in such a way， the individual teeth and the individual tooth units are connected to form a whole. In the process of drilling， the working lips of the bit teeth will produce multiple stress concentration zones that exceed the ultimate failure strength of rock， but are much lower than the strength of the bit matrix. It is not prone to produce a few stress concentration zones that approach or exceed the strength of the bit body. As a result， the bit provides better integrity， more uniform force， more efficient rock cutting， longer life， and better slippage resistance， especially in hard formations. The field experiment shows that the bionic self-compensating integrated high-matrix impregnated diamond coring bit has higher rock breaking efficiency and longer service life than the conventional bit.

Abstract:Reaming while drilling is a key step of the casing while drilling process in ocean drilling， while the expandable underreamer can effectively realize casing drilling through control of opening and closing of the reaming arms by pressure difference with large reaming size. The cantilever reamer with locking function in place was designed with the offset jet port arrangement for cleaning the arms. The computational fluid dynamics technology and the standard k- turbulence model were used to simulate and analyze the flow field of the jet ports at different angles and diameters. The simulation results showed that the fluid velocity and the dynamic pressure acting on the cutting teeth of the reaming arms were comprehensively affected by the jet port angle and diameter， and annulus drilling fluid. With the jet port angle α increasing from 40° to 90°， the fluid velocity acting on the cutting teeth changes in a cosine like curve. With the jet port diameter d increasing from 4mm to 10mm， the fluid velocity and the dynamic pressure acting on the cutting teeth change in a parabola shape. Considering the cleaning effect， machining properties and the interaction between the jet fluid and the annulus drilling fluid， optimization was carried out to determine α=70°and d=8mm. The test over land and at shallow sea showed that the structure and the function of the expandable underreamer were feasible， with the reaming size meeting the requirements of normal drilling with casing， and the optimized jet port angle and diameter achieving good cleaning of the arms to effectively prevent bit balling. The research results can provide a reference for the design of underreamers with different specifications in ocean drilling.

Abstract:In the process of pressure transfer of gas hydrate core samples， the core capture device is the key to realize sample transfer. Core capture is carried out in the core tube， which belongs to the non-visual operation process. At the same time， the core sample and the capture device are in high pressure liquid. The gap between the core liner and the core tube is very small. To ensure the in-situ state of the core sample， there are high requirements for the structural design， accurate positioning， rapid capture and release of the core capture device. According to the capture， drag， positioning and release functions required by the device， the hanging plate self-locking and the contact unlocking mechanisms are designed， and the probe is used to capture the liner. Indoor capture experiment shows that the mechanism can successfully capture and unlock the core. The structure is simple， and the core can be transferred at pressure， which accelerates the research progress on the pressure transfer device of natural gas hydrate.

Abstract:The ?215.9mm four-cone coring bit is a cone coring bit designed and produced under the project of "Deep Sea Drilling Technology And Engineering Support"， and is mainly used for high-efficiency and long-run coring in hard rock and complex strata. By reasonably arranging the cone angle and distribution， and optimizing the coring structure， core recovery can be effectively improved to ensure the drilling rate and reliability of the bit in hard rock. Land test and marine test had been conducted for continuous optimization and improvement of the bit； and experimental geothermal exploration coring was carried out for the first time in Qingshuihe county， Hohhot city， Inner Mongolia autonomous Region. The whole coring section is granite of high abrasiveness and high hardness， and difficult to core. With the combination of the ?215.9mm cone coring bit with conventional coring tools， drilling speed reached 1.2m/h with core recovery of 70%~90%. It has good application value and can provide technical support for marine drilling hard rock coring.

Abstract:A seawater-based drilling fluid has been developed through selection of key additives such as fluid loss reducers， high-temperature stabilizers， and optimization of the components to deal with the problems encountered in deep drilling， such as instability of the borehole wall， unstable rheological properties of drilling fluid， and large fluid loss. The comprehensive performance of the drilling fluid was analyzed， and the results showed that the drilling fluid with density of 1.5g/cm³ had an apparent viscosity change rate of 2.5% after aging for 16h at 230℃， and the HPHT filtration loss was 23mL； indicating that the seawater drilling fluid could resist temperature up to 230℃ with good high-temperature stability， high-temperature rheological properties and low filtration loss at high-temperature and high-pressure， and it can meet the requirements of deep-sea high-temperature drilling.

Abstract:Deep sea drilling is often accompanied by high temperature and high pressure， which puts forward new requirements for plugging materials for drilling. The HTD-3 high temperature plugging material was produced through the high temperature resistance screening of granular， fibrous and flaky leakage plugging materials. Then， the DL-3A high temperature plugging evaluation instrument was used to test the temperature resistance， pressure bearing and plugging performance of the plugging material. SEM was used to observe and analyze the bridging condition of the plugging material. Finally， the compatibility test was carried out at 5% gradient concentration. The results show that the HTD-3 high-temperature plugging material has some impact on drilling fluid density， but has little impact on other basic properties of drilling fluid. In this material， granular materials with different sizes completed bridging， fibrous and flaky materials completed filling， forming a high-strength plugging wall. HTD-3 high-temperature plugging material not only has a good temperature bearing and pressure bearing capacity， but also has a good sealing performance with plugging effect. The development of HTD-3 high temperature plugging material provides a feasible choice for deep-sea drilling plugging in the future.

Abstract:In view of hard rock drilling difficulties in fracture zones during ocean drilling， and with the summary of the main technical difficulties and solutions in drilling of the fracture zone formation at home and abroad， this paper analyzes the characteristics of the fracture zone formation often encountered in the construction with regard to field cases， and proposes a new idea of applying chemical gel technology to solve complicated problems in fractured zone formation. The basic formulation of the chemical gel system suitable for different formation temperatures has been developed. Through orthogonal experimental design， a complete operation procedure for high temperature resin gel wall protection has been formed for deep-sea drilling.

Abstract:Subsea hard rock is the stratum that ocean drilling will inevitably encounter to achieve the goal of “Moho Drilling”. During the many ocean drilling expeditions， hard rock were encountered subsea many times. Not only have core samples been collected， but also many problems have been discovered in the drilling operation. This article collects data on subsea hard rock drilling expeditions in ocean drilling carried out in recent years， including 309， 312， 335， 360 and 384. A brief review of the expeditions is made with focuses on the challenges encountered in the current subsea hard rock drilling in terms of drill bits， wellbore stabilization and coring tools， as well as the solutions； and a prediction is also made of the development of subsea hard rock drilling in the future.

Abstract:High-temperature geothermal power generation is a promising industry that has received great attention from countries all over the world in recent years in the context of the global energy transition. To realize the development of high-temperature geothermal energy， the related drilling technology is the key. Since the 1950s in North America， continuous research and experiments have been conducted on technologies that utilize geothermal energy for commercial direct use and power generation. A complete technology system has been formed in high-temperature geothermal drilling， such as high-temperature geothermal well design and wellbore integrity technology， high-temperature and ultra-high-temperature hard rock drill bit design and manufacturing technology， high-temperature down hole drilling tools， high-temperature downhole measurement tools， high-temperature mud system and circulation loss prevention technology， high temperature cement slurry system and high temperature well control technology， etc. This article will combine the author''s work experience in both China and North America， to give an overview of the key technologies and challenges of geothermal drilling in North America.

Abstract:In order to reveal the influence of mined-out areas formed by solid mining on replacement performance of gas hydrate CO₂ replacement mining， the comparative experimental study on CO₂/N₂ replacement mining of different gas hydrate saturations in mined-out area reservoirs and intact reservoirs was carried out. The results show that for the samples each with hydrate saturation of 30% and 45%， the CH₄ replacement rate of the mined-out area-reservoir is 5.5% and 9% higher than that of the intact reservoir， and the CO₂ storage per unit volume is increased by 26.5% and 39.8%， respectively. The existence of mined-out areas increases the molar ratio of the replacement medium to gas hydrate， thus providing a higher replacement driving force. Moreover， in the samples with high hydrate saturation， the mined-out area will also improve the diffusion of the replacement medium， resulting in the greater replacement effect of the reservoir containing mined-out area over the intact reservoir. Therefore， CO₂ replacement mining after solid mining can improve replacement mining efficiency， and contribute to carbon sequestration and formation stability. It is a potential safe and green mining mode for marine hydrate.

Abstract:As energy consumption continues to rise， and conventional resources cannot meet daily needs， deep well drilling is particularly important. However， problems such as increased viscosity of drilling fluid， deterioration of rheology caused by high temperature at the bottom of the well have made the high temperature resistant viscosity reducer one of the indispensable drilling fluid treatment agents. To reduce the viscosity of the drilling fluid and improve the rheology， viscosity reducers mainly disassemble or block the formation of the grid structure between clay particles. In reference to the relevant research literature， this paper summarizes the research status of domestic drilling fluid viscosity reducers in the past ten years with emphasis on three types of viscosity reducers： synthetic polymers， modified natural materials， and industrial waste-made viscosity reducers. In view of the current problems， it is pointed out that in the future， low-cost and environment-friendly viscosity reducers suitable for high-temperature， high-salt and high-density drilling fluids should be developed at the molecular structure design level. At the same time， it pays attention to the utilization of industrial waste and the speeding up of the technology transformation through field applications. In recent years， synthetic polymer viscosity reducers have been studied mostly and developed the fastest. This article focuses on the development status and prospects of this type of viscosity reducer.

Abstract:Drilling problems， such as melting permafrost strata， expansion and collapse of hole walls， less drilling depth， core taking difficulty， borehole freezing， are encountered in the process of drilling due to the characteristics of strata and the fact of the plateau permafrost environment of Dongchenggongma. Drilling equipment， drilling technology and drilling management was investigated with the focus on the effect of low-temperature drilling fluid properties on drilling process. Orthogonal experiment was conducted to compare the formulation of flushing fluid at -5℃ to select the optimum formulation with low temperature resistance， small heat dissipation coefficient， proper viscosity and low filtration loss， and it effectively solved the drilling problem in plateau permafrost strata. Field use in two boreholes of CZK031 and CZK4821 showed the hole wall was well protected by the drilling fluid， and no collapse and freezing accidents occurred， achieving good drilling effect. The research and application of low-temperature drilling fluid formulation can provide reference for drilling in plateau permafrost strata in other areas.

Abstract:In the context of the great demand for subsurface new energy exploration in China， the major science and technology special project of "5000m Intelligent Drilling Equipment and Technology for New Energy Exploration" funded by Anhui Province has been completed， and delivered a series of achievements such as 5000m multifunctional AC frequency conversion electric drilling rig， multi-parameter hole bottom automatic monitoring device， high-temperature environmental protection mud and mud performance automatic measurement device， coring to full-face drilling interchangeable drilling tools without lifting the drilling string； filling the domestic gap， and driving forward the development of new energy deep drilling technology to the direction of intelligence.

Abstract:Excessive vibration frequency will damage drilling tools， affect efficiency and even cause downhole accidents， so it is necessary to measure the vibration frequency of downhole drilling tools in real time. In this paper， a high temperature resistant downhole vibration sensor based on the triboelectric nanogenerator is proposed. The sensor has not only vibration measurement function， but also power generation function. When the sensor measured the vibration frequency， the test showed that the measurement range was 0~8Hz， the measurement error was less than 4%， the signal/noise ratio was high， the anti-interference ability was strong， and the output signal amplitude was inversely proportional to the distance between the sensor and the vibration source. When the sensor was used for power generation， the test showed that the higher the vibration frequency， the greater the power generation. Its output voltage， output current and output power at 8Hz were 70V， 12×10^-7A and 4.2×10^-5W， respectively， demonstrating its potential as a downhole distributed generator. In addition， the sensor can be used at temperature less than 180℃ and relative humidity less than 90%， exhibiting strong adaptability.

Abstract:Emergency rescue technology in mines and underground works has developed rapidly in recent years， and it has been found that the mode of the small diameter life support hole combined with large diameter rescue wells is an effective way to carry out mine disaster rescue. With the drilling technology for life support holes in mine disasters as the main subject， this paper analyzes the typical structural design of the small diameter life support hole and casing selection， describes mud direct circulation drilling， air DTH hammer reverse circulation drilling， and presents drilling difficulties in the case of the rescue of Qixia Hushan Gold Mine. In view of the deviation of the No. 3 life support hole in the rescue， based on the trajectory design theory， the ultra-short-distance spiral correction technology was innovatively proposed. The method has achieved good results， and provides valuable experience for subsequent life support hole construction.

Abstract:Geo-technical investigation of the Shiziyang main channel in the Guangdong-HongKong-Macao Greater Bay Area cannot be carried out with vertical point drilling. Therefore， an extended-reach novel horizontal borehole with high horizontal displacement/vertical depth ratio was designed for investigation： designed hole depth of 940m， 14 coring targets， target radius of 5.0m， horizontal section length of 380m， vertical depth of 60m， and horizontal displacement/vertical depth ratio of 14. It is one of the boreholes with the most working targets per single hole and the highest horizontal displacement/vertical ratio in China. A set of comprehensive exploration technologies， including multi-target directional drilling， undisturbed coring by the mud motor， geological logging and drill string-conveyed storage logging have been developed， and applied for the first time in water conservancy and hydropower investigation with good results. The completed drilling depth of the hole was 932.20m， and the target hit rate was 85.71% with the coring footage of 81.71m， the penetration rate 2.38m/h， and the core recovery rate 89.84%. With the novel drilling technologies， accurate advance geological prediction of the main channel on the ocean floor was achieved with great reduction of the number of exploration holes， less environmental damage， higher exploration efficiency； and the continuity and reliability of geological data was ensured. It is an advanced technology worth popularizing in tunnel exploration.

Abstract:In the process of large diameter pile hole construction for landslide treatment， rapid drilling is the key to success. Therefore， the selection of appropriate drilling tools and technology is extremely important， and the pneumatic DTH hammer is widely used because of high drilling efficiency. With the pneumatic DTH hammer drilling process， the spherical teeth on the bottom of the bit break rocks to achieve high drilling efficiency； however， inappropriate selection of impact energy for the spherical teeth can lead to increased energy loss， quick tooth wear and low drilling efficiency. Appropriate selection of impact energy is of great significance to rock fragmentation. In this paper， ABAQUS software is used to simulate the rock impact process by a single spherical tooth， and the free-fall impact experiment is carried out on the impact hammer to analyze the rock fragmentation mechanism of a 19mm diameter spherical tooth by at different impact energy， together with the change pattern of the broken area. The results show that the rock crushing mechanism can be divided into three stages： elastic deformation， fracturing and volume crushing. When the spherical teeth drills granite at 30 J impact energy， energy loss can be effectively reduced and rock crushing efficiency can be improved.

Abstract:Although impact drilled cast-in-place piles have wide applicability in all kinds of strata， holes are prone to deviat under complex geological conditions. In view of frequent deviation of holes in the construction of impact drilled cast-in-place piles for a high-rise building， hole deviation in the impact drilling process is comprehensively analyzed and studied. With hole deviation correction and prevention as the subject of study， research was carried out for two specific cases： deflection from solitary stones and dipped hard rock stratum. For solitary stones， the bit， impact stroke and frequency were properly controlled； for dipped hard rock stratum， increase of the thickness of the TC chips was studied for the bit. Field application demonstrated that hole deviation was effectively avoided.