Abstract:Ocean drilling has been carried out for more than 50 years. Not only have a large number of cores been drilled to promote the progress of Earth Science， but also the application of long-term borehole observation systems has provided valuable data for multidisciplinary research. This paper comprehensively reviews various long-term borehole observation systems since the implementation of ocean drilling， and focuses on analyzing the structures and installation details of the Smart Plug and the Genius Plug micro-observation systems and the LTBMS long-term observation system equipped on the Japanese “Chikyu” drilling ship. These systems can capture storm， tsunami and earthquake signals， and the networked data of LTBMS also reveals the correlation between pore pressure changes and crustal deformation. For example， by analyzing the temperature and pressure data monitored by the Smart Plug， the relationship between transient pressure and earthquakes and tsunamis can be studied； by comparing the pressure data of different systems， it can be determined whether the crust has deformed； and by synthesizing the data of multiple networked borehole observation systems， it is helpful to explore the earthquake nucleation mechanism. Deeply exploring the functions of these systems and the practical experience of Japan has important implications for the research and development of related systems in China， and is of great significance for a deeper understanding of the tectonic evolution of the earth and the laws of earthquake activities.

Abstract:The influence of different polycrystalline diamond compact （PDC） cutter geometries on drilling efficiency has drawn significant research attention. Substantial improvements in rock-breaking efficiency and bit durability can be achieved through optimization of cutter structural design and enhancement of material properties. Recent advancements in materials science， manufacturing technology， and numerical simulation have facilitated notable progress in the application of non-planar PDC cutter geometries for drilling efficiency. This paper systematically reviews research advancements in rock-breaking mechanisms， cutter layout design， and field applications of special-shaped cutters through experimental and numerical investigations. Furthermore， it proposes recommendations for future development directions， aiming to provide valuable insights for enhancing PDC drilling performance. The comprehensive analysis integrates fundamental mechanisms with practical engineering considerations， offering a scientific framework for optimizing cutter configurations in the challenging formation drilling scenarios.

Abstract:Drilling is a process of rock fragmentation practically. In the rock fragmentation process， on the one hand， the bit fragments the rock， on the other hand， the rock resists the fragmentation. Both aspects should be considered. In the past， the research on how drill bits fragment rocks has been extensive， but research on how rock resists fragmentation is insufficient. Impregnated diamond bits can be used to drill rocks with drillability grades 6 to 12. Their application scope is wide. Impregnated bits usually contain small-sized diamond cutters. Russian drillers have studied rock fragmentation resistance during drilling with small-sized diamond cutters and proposed using the resistance coefficient to analyze how rocks resist fragmentation. Understanding this coefficient can help address issues such as the dependence of technical indexes on drilling parameters， how to improve drilling results， what kind of state the rock fragmentation is in and to determine how to increase technical and economic indexes of drilling and so on. In China， the research on the resistance coefficient is insufficient and there are no relevant research reports. Therefore the research has certain reference value and practical significance. It is suggested that this research topic be explored to confirm its importance in improving the results of rock fragmentation and increasing the technical and economical indexes of drilling engineering in China.

Abstract:Deep-sea oil and gas wells often traverse natural gas hydrate formations. Due to the stable existence of natural gas hydrates under low temperature and high pressure conditions， the hydration heat of cement slurries can lead to the decomposition of hydrates around the wellbore， resulting in serious wellbore accidents. Moreover， hydration heat can induce thermal stress in the cement sheath， causing cracks and reducing the sealing capability of the cement sheath， ultimately leading to decreased cementing quality. In this study， low-carbon chain mixed alkanes were used as phase change materials and epoxy resin as the base material for crack suppression. A temperature-controlled self-healing microcapsule suitable for cement slurries in hydrate formations was prepared by the surface coating of calcium carbonate and stearic acid using a self-assembly method and a condensation method. The basic properties of the microcapsules were characterized using DSC， TG， optical microscopy， heat cycle tests， and fracture surface adhesion tests. The performance of the microcapsules in controlling temperature and suppressing cracks in cement slurry systems was investigated through rheological property tests， hydration heat rise tests， changes in the mechanical strength of cement stone， and crack development assessments.

Abstract:The development effect of water flooding in tight sandstone reservoirs is closely related to the morphology of water flooding front， so accurate prediction of the water flooding front topography is the key to evaluating the water flooding development effect of tight sandstone reservoirs. Most current water flooding front evolution models assume that the reservoirs are homogeneous and do not consider the microstructures of the reservoirs， so they cannot effectively predict the evolution law of the water flooding front in tight sandstone reservoirs. In this work， by combining the water flooding front morphology evolution tests， and the fractal theory， the evolution of the average displacement and the fractal dimension of water flooding front in tight sandstone reservoirs are studied. On this basis， by combining the Langevin equation， the stochastic theory， and the Buckley-Leverett theory， a theoretical model for predicting the water flooding front evolution in tight sandstone reservoirs is established. The results show that the theoretical calculation is in good agreement with the experimental results， which verifies the correctness of the theoretical model. The boundary position of water flooding front in tight sandstone reservoirs is influenced by the macroscopic average displacement （controlled by the Buckley-Leverett theory） and the fractal dimension of water flooding front topography （controlled by water phase viscosity and rock heterogeneous pore structures）. The results reveal the physical and mechanical mechanism of complex displacement boundaries caused by water flooding in tight sandstone reservoirs.

Abstract:Drilling technology is an indispensable technical support for deep resource exploration， and the prediction of drilling efficiency is an important way to improve drilling technology. In response to the requirements for drilling speed-up in a certain block in the South China Sea， this paper collected actual drilling data from 10 wells， and these data were first interpolated and normalized. In order to eliminate the high correlation among different parameters， the initial 43 parameters were reduced to 21 common factors based on factor analysis， where there was no correlation between the 21 factors. Based on well number and depth， combining with a 10-fold cross-validation scheme， stratified sampling and grouping were performed on the original data. Through an optimized structure with a single hidden layer and 15 neurons， two neural network models were established on the basis of whether a hydraulic motor was used， and they both achieved an accuracy of over 96%. The model prediction shows that the use of speed-up tools in the target block with low silica content can effectively improve the drilling efficiency. At the same time， the model also predicts that for the high silicon content section， the use of speed-up drilling tools will increase wear on the drilling tools and cause a decrease in drilling speed. The results of the study show that the drilling speed prediction model based on a neural network can effectively make up for the differences among wellbores. Through accurate drilling speed prediction， it is possible to efficiently evaluate the effect of using speed-up tools and improve drilling efficiency.

Abstract:During the solid-liquid separation of drilling fluids， solid-phase particles such as drill cuttings will cause serious wear failure and dynamic balance instability to the key components of the centrifuge， affecting the separation effect and shortening the service life. The internal flow field characteristics of the drilling fluid centrifuge are simulated based on the dense discrete phase model （DDPM） and the RNG k-ε turbulence model. The erosive wear performance of key components was predicted in combination with the Finnie erosion model. The effects of rotational speed， particle concentration， and medium viscosity on the erosion wear performance of the components were explored. The results show that the erosion is mainly concentrated on the blades of the screw conveyor near the feed cavity and at the bowl cone. The erosion rate of the centrifuge components rises as the rotational speed increases. Elevated particle concentration exacerbates the erosion of the components. While erosion on the inner wall of the bowl is reduced by an increase in medium viscosity， screw wall erosion is intensified. The research results provide valuable insights into the erosive wear characteristics of centrifuges and recommendations for optimizing the operation and maintenance of centrifuges in practical applications.

Abstract:In recent years， the geothermal sector in China has witnessed rapid growth， and the significance of the development and utilization of geothermal resources has significantly escalated. To effectively drill medium-deep geothermal wells in complex strata， this paper focuses on the technical drilling issues that arise in medium-deep geothermal wells when penetrating water-sensitive strata， water-gushing strata， fractured and loose complex strata， as well as high temperatures within the boreholes. Based on a large number of experiments， an initial selection of high-temperature-resistant drilling fluid formulations was made. The optimal formulation was determined through orthogonal experiments. Through effective tests， the water loss of the drilling fluid at a high temperature of 120℃ in the well was 8.4mL， the funnel viscosity was 24s， the yield point was 1.43Pa， the apparent viscosity was 14.5mPa·s， the plastic viscosity was 13.1mPa·s， the pH value was 8， the density was 1.04g/cm³， and the anti-aging performance of the drilling fluid flowing for 48 hours at 120℃ was excellent. It indicates that the high-temperature-resistant drilling fluid developed for medium-deep geothermal well drilling （around 3000m） can meet the requirements of medium-deep geothermal well drilling， featuring good rheological properties， high-temperature resistance， anti-aging properties， and water loss and wall-building properties， and can effectively address the problems encountered during the drilling of medium-deep geothermal wells in complex strata.

Abstract:Coalbed methane content is a critical parameter for characterizing coal reservoir properties. The most direct and effective way to improve the accuracy of the test results of coalbed methane content is to use sealed pressure-holding coring technology， wherein the coal core sample is sealed inside the drilling tool and lifted to the ground for desorption. This paper proposes a technical scheme for a wireline-retrievable lifting and tilting ball valve type sealed pressure-holding coring drilling tool used for crushed soft coal seams. The working mechanism and key technologies of the sealed pressure-holding coring drilling tool are studied， and the overall structural scheme of the sealed pressure-holding coring drilling tool， the structural design calculation of the main components， preliminary indoor experiments， and optimization improvement plans are elaborated in detail. Research and experiments have shown that the sealed pressure-holding coring drilling tool has a simple structure， good sealing effect， easy operation， and can obtain the maximum feasible core diameter （a core diameter of 50mm can be obtained from a 118mm diameter borehole）； The precise fit between the lever and the ring that drives the ball valve to flip is an important factor in determining whether the ball valve can smoothly flip and seal.

Abstract:The total reserves of shallow and mid-shallow oil and gas resources in China are dwindling due to continuous exploitation. Enhancing exploration and development of deep and ultra-deep oil and gas resources is crucial for ensuring national energy security. Drilling in deep and ultra-deep high-temperature formations poses inevitable engineering challenges， necessitating the development of lightweight， high-strength， and temperature-resistant drill pipe materials. In this study， SiC particle-reinforced 2A12 aluminum alloy drill pipe materials， with short carbon fibers incorporated， were prepared through vacuum hot-pressing sintering， hot extrusion， and heat treatment processes. The mechanical properties of composites with varying SiC volume fractions were evaluated under different temperatures. Results indicate that the mechanical properties of SiC/2A12 aluminum alloy composites with a 3% SiC volume fraction at 25℃ are the best， and the tensile strength is 10.8% higher than that of 2A12； the mechanical properties of SiC/2A12 aluminum alloy/carbon fiber composites with a 5% volume fraction at 180℃ and 220℃ exhibit superior performance， with corresponding increases in tensile strength of 17.9% and 19.2%， respectively. The incorporation of SiC particles and carbon fibers increases the operational temperature of the 2A12 aluminum alloy by 40℃. The primary strengthening mechanisms are Orowan strengthening for SiC particles and load transfer for carbon fibers.

Abstract:Fracture-cavity formation malignant leakage is one of the most common and difficult to control drilling in engineering. To solve the problem of the lack of indoor evaluation means for fracture-cavity type malignant leakage， a new visualized evaluation device for fracture-cavity type malignant leakage was developed. The maximum experimental temperature was 180℃， the maximum simulated length of fracture-cavity was 60cm， the maximum rated experimental pressure was 5MPa， and the maximum diameter of the filling and plugging module was 5cm. The evaluation experiment of 1cm and 2cm gravel simulated plugging was carried out by using the new visualized fracture-cavity type malignant leakage evaluation device， and the optimal plugging system formula suitable for the 1cm and 2cm gravel simulated fracture-cavity system was formed. The formula optimization of DY9 well plugging system was carried out， and the on-site plugging pressure reached 5MPa， and the plugging was successful once. The research shows that the sealing layer can be visually evaluated by the new visualized fracture-cavity malignant leakage evaluation device， which is convenient for the optimization of the plugging slurry formula. The reasonable combination of "rigid material + fiber material + elastic material" in the plugging system can form a dense pressure sealing， so as to realize the effective plugging of the fracture-cavity.

Abstract:The Nam Co Drilling Project in Tibet is a scientific drilling program implemented by the Institute of Tibetan Plateau Research， Chinese Academy of Sciences， in collaboration with the International Continental Scientific Drilling Program （ICDP）， which is a scientific drilling initiative aimed at retrieving lacustrine sediment cores from Nam Co to study and monitor climate change and global environmental dynamics. During this project， drilling operations were conducted at a water depth of approximately 100 meters， with the deepest borehole penetrating lakebed sediments to a depth of 700 meters. This paper investigates the primary technical challenges of lake drilling in Nam Co by examining the design and operational procedures for lake drilling platforms， including： platform design and modular assembly； anchor positioning； drilling equipment selection； polymer anti-collapse drilling fluids； P-diameter wireline coring tools； deepwater casing systems； and airbag-type casing centralizer designs. Centered on the demand for lake drilling capabilities with a maximum depth of 800 meters （including water depth of 100 meters）， this study develops relevant drilling technologies and equipment using a case example of a 250 meters borehole （including water depth of 100 meters）. The research provides critical technical support for the Institute of Tibetan Plateau Research， CAS in advancing studies on global climate change， biological evolution， tectonic evolution， paleomagnetic variations， and hydrological cycles.

Abstract:In order to complete the comprehensive investigation project of ecological restoration of Dongting Lake wetland， a standard sampling borehole was constructed， which runs through the Quaternary loose mud， sand and gravel layers in the Dongting Lake area， requiring accurate coring throughout the borehole. The construction task was successfully completed by adopting comprehensive measures such as increasing the coring diameter， using small-diameter dry drilling for core extraction， and large-diameter casing wall protection. The core recovery rate reached over 95%， and the core was basically uncontaminated. A field application test was conducted about the aperture type special coring tool， and the test results showed that the drilling tool can achieve better fidelity coring effect. However， there are still shortcomings such as insufficient length of the core tube， which provides a basis for the improvement and promotion. Through the construction of this borehole， a set of sampling techniques suitable for loose mud， sand and gravel layers in the Dongting Lake area has been explored， laying the foundation for the study of Quaternary ecological geology in the lake area.

Abstract:Shallow shale gas resources in Wulong are poorly endowed and difficult to develop efficiently. Increasing the length of the horizontal section and drilling large-displacement horizontal wells are important means to increase the production of single well. In view of the technical difficulties faced by shallow shale gas large-displacement horizontal wells， such as difficulty in optimizing the casing program， high safety risk of drilling tools， high requirements for drilling fluid performance， difficulty in lowering casing， and high risk of well completion loss， we have carried out wellbore structure optimization based on accurate prediction of four pressure profiles， analysis of drilling tool safety extension capacity， optimization of water-based drilling fluid system suitable for shallow shale， optimization of casing lowering methods， and optimization of completion cement slurry column structure， forming key technologies for drilling large-displacement horizontal wells for shallow shale gas. The research results were applied on site in 6 wells of the PY1 platform， with an average well depth of 3188m， a vertical depth of 1000~1200m， a horizontal section length of 1532~2250m， a horizontal-to-vertical ratio of 1.59~2.64， and an average mechanical drilling speed of 17.82m/h. This achieved fast drilling and safe well completion， and provided technical support for the efficient development of the Wulong shallow shale gas block.

Abstract:Aiming at the complex problem of mudstone formation leakage and collapse in Liujiagou， Shiqianfeng and Shihezi Formations in Jin 30 Well Area of Dongsheng Gas Field， indoor rock analysis and physical and chemical performance tests are conducted， revealing that the mudstone formations have the characteristics of high clay mineral content， multi-scale fracture development， and are prone to clay hydration expansion and fracture expansion during drilling. A wellbore stabilization technology with the core of inhibiting clay hydration swelling and strengthening multi-scale fracture plugging is proposed. Through the verification of indoor research and field application， effective control of hard and brittle mudstone in the long open hole sections is realized by the developed multi-salt ratio high-performance compound salt drilling fluid， and the wellbore stability is significantly improved. Compared to the year 2023， the drilling period of horizontal wells with pilot hole in the year 2024 was shortened by 37.4%， which provides technical support for efficient drilling in mudstone formation in Jin 30 Well Area of Dongsheng Gas Field. The research results also provide theoretical basis and practical reference for oil and gas exploration and development under similar geological conditions.

Abstract:This paper conducts an in-depth study on the drilling problems of soft mudstone strata in typical clastic halitite deposits in Shashi salt deposits in Jiangling Sag of Jianghan Basin. Through the analysis of the characteristics of the salt-bearing strata in and the actual drilling data of salt wells， the influence of soft mudstone on the safety， efficiency and quality of drilling engineering was systematically summarized. Based on this， a series of targeted drilling engineering technical countermeasures are proposed， such as the use of high-density undersaturated brine drilling fluid to balance the formation pressure， cone bit+screw+back reaming tool combination， and the testing drilling method of “retreat as advance”. These countermeasures have been applied in the actual drilling process， providing safety and quality assurance for subsequent construction， effectively reducing the probability of downhole complex conditions， and also providing important references for other drilling projects under similar geological conditions.

Abstract:In the Linxing Block， multiple coalbed series with strong heterogeneity are vertically developped in directional wells. Conventional fracturing technology fails to achieve uniform reservoir stimulation， leading to over-expansion of high-permeability intervals and insufficient stimulation of low-permeability intervals， which seriously affects development efficiency. By reasonably optimizing the fracturing design parameters of Well LX36-XXD in the block， soluble knot-type temporary plugging balls were used to realize temporary plugging fracturing. After temporary plugging， the construction pressure increased significantly， verifying the rationality of the fracturing scheme design. The fracture morphology simulation showed that after adding temporary plugging agents， both No.8 and No.9 coal seams were effectively stimulated， with obvious temporary plugging balanced fracturing effects. The effective stimulated reservoir volume （SRV） increased by 18.2%， and the initial production reached 0.8×10?m3/d. This verifies the adaptability of temporary plugging balanced fracturing to reservoirs with strong heterogeneity， demonstrating significant technical advantages. It provides an important technical reference for the efficient development of deep coalbed methane， and its promotion value in tight-cut fracturing of horizontal wells can be further explored in the future.

Abstract:Aiming to address the core challenges in long-distance directional drilling technology， such as difficulties in controlling borehole trajectories and low efficiency in continuous coring， this paper presents the application of Long-distance Directional Continuous Coring （LDC） technology in Singapore’s HDC3-1 geotechnical investigation project. By optimizing and integrating the Directional Coring Drilling （DCD） process with the NQ wireline coring method， this technology enables simultaneous long-distance directional drilling and continuous coring within the target borehole intervals. Compared to traditional investigation techniques， LDC offers advantages including controllable borehole trajectories， continuous sampling， shorter project timelines， lower comprehensive costs， and minimal environmental impact. The successful implementation of this innovative technology has demonstrated its feasibility and practicality， providing enhanced approaches and method for geotechnical investigation.

Abstract:To address the complex geological conditions in the deep boreholes of a railway tunnel survey in Enshi， Hubei， including karst cave development， severely fractured rock masses， and persistent fluid loss， a multi-diameter casing pipe reaming drilling technique combined with casing isolation technology is proposed as an effective solution for traversing the upper karst cave formations. This paper introduces the handling method for drilling tool falling （drill string runaway） accidents， analyzes the application effectiveness of conventional low-solid-phase flushing fluid， special flushing fluid for carbonaceous limestone sections， and fractured zone flushing fluid. In addition， it elaborates on the mechanism by which the polyvinyl alcohol （PVA） stabilizes borehole walls through adsorption， cementation， and film-forming. In the meantime， the primary causes leading to the abandonment of three boreholes are summarized. This establishes a technical paradigm for safe drilling in karst development zones for similar deep-hole drilling in railway tunnels.

Abstract:This article is based on the engineering practice of deep muddy soft soil layers in the Wenzhou area， and proposes a series of improved and optimized measures to address the problems of difficult alignment of pile drivers， insufficient accuracy of steel insertion， and high construction costs in SMW pile construction. By improving the method of aligning the displacement of the pile driver with the insertion of the steel， and utilizing the relative displacement and markers between the track shoe and the retaining cover plate， the pile driver was quickly and accurately positioned. The insertion method of steel sections has been optimized by using a combination of pile driver auxiliary crane and excavator light pressure， which reduces the construction costs and improves the efficiency. In addition， by setting up steel guide locators and bearing type guide devices， the verticality and center position of steel insertion have been effectively controlled. Practice has shown that the improved construction method significantly improves the construction efficiency （from 22~25 pieces/day to 38~40 pieces/day）， reduces the machinery and labor costs， and minimizes the impact of noise and vibration on the surrounding environment. The research results provide practical and feasible technical references for the construction of SMW method piles in silty soft soil layers.