Fractures are important seepage channels in oil and gas extraction and are the key to efficient resource exploitation. However, with the extensive development of fractures, they have also become the main cause of severe drilling fluid and oil and gas leakage. In order to enhance the leakage control of fractured strata, the plugging mechanism was studied through the computational fluid dynamics - discrete element method (CFD-DEM) numerical simulation. This paper focused on the spherical particle diameter, concentration dose, gradation, fluid density and velocity. The research found that for monodisperse particles, under the condition of R = 0.4, the best blocking efficiency can be achieved through sequential double-particle bridging. A concentration of 15

Drilling fluids are indispensable to the drilling process, commonly referred to as its 'lifeblood.' The presence of elevated downhole temperatures presents substantial challenges for drilling engineers. This study introduces a novel phase change microcapsule with a core-shell structure, meticulously designed to address these challenges. The microcapsules were synthesized using the water-in-oil-in-water (W/O/W) complex emulsion solvent evaporation technique, incorporating erythritol as the core material and polysulfone as the shell. The phase change enthalpy and temperature were measured at 235.3 J/g and 121.9 degrees C, respectively. The incorporation of 5 wt% MEPNs could decrease the downhole circulating temperature by up to 6-7 degrees C.The shell demonstrated excellent shear(with a breakage rate of 13.2 % at 15,000 rpm) and corrosion resistance, retaining over 90 % of its effectiveness after 25 recycling cycles. With a particle size of less than 75 mu m, these microcapsules can be effectively integrated into drilling fluids to enhance cooling without compromising their performance. This groundbreaking approach offers a promising solution to the high-temperature issues encountered during shale gas extraction, thus contributing significantly to the advancement of drilling fluid technology.

Under long-term high-temperature and static conditions, high-density workover fluid settles, increasing the risks of workover operations. In order to achieve a quantitative assessment of the sedimentation stability of oil well workover fluids, this study adopted spectral analysis to conduct stability tests on water dispersions of barite with different concentrations. Meanwhile, a comprehensive assessment was conducted on the sedimentation rate of the well repair fluid, the size of solid particles and the changes in the thickness of the sedimentary layer in 1# Well, 2# Well and 3# Well. With the increase in barite concentration, its sedimentation behavior changes from free sedimentation at low concentrations to flocculation sedimentation at high concentrations, and the sedimentation rate shows a slowing trend. The increase in sedimentation rate is positively correlated with the increase in density, and the intensity of the initial backscattered light at the bottom of the well also increases accordingly. In addition, during the sedimentation process of sediment, the variation pattern of particle velocity shows the characteristics of being relatively fast in the early stage and gradually accelerating in the middle and later stages. The results show that the average particle size of barite solution is 4.93 μm, and the average particle size of the three workover fluids is 87.5 μm. The deposition thickness range of barite solution is 5–50 mm, and that of the three workover fluids is 25–51.58 mm. It provides data support for the rapid quantitative evaluation of the long-term stability of oil well workover fluids.

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The effective control of water-based drilling fluid filtration rates in deep and ultra-deep wells poses a significant challenge. This study introduced a novel approach utilizing pullulan microsphere (PM) grafted with N,Ndimethylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and dimethyl diallyl ammonium chloride as a filtrate reducer (PM-DAD). The polymer's structure was analyzed through Fourier transform infrared spectroscopy, nuclear magnetic resonance, thermogravimetric analysis, and scanning electron microscopy. Structural characterization confirmed the successful polymerization and good thermal stability of PM-DAD. PM-DAD showed the pH response characteristics of particle size decreasing with the increase of alkalinity and the temperature response characteristics of degradation into nanoparticles after high temperature aging. The filtration loss and rheological properties of PM-DAD were assessed in accordance with the American Petroleum Institute standards. The rheological evaluation results indicated that PM-DAD could effectively maintain optimal rheological properties of the base mud after aging. PM-DAD showed remarkable filtration loss reduction ability. After aging at 200 degrees C, the filtration loss of the base mud was 4.7 mL, and that of the base mud containing 15 wt% NaCl was 8.2 mL. The filtration reduction mechanism of PM-DAD was investigated through mud cake analysis, particle size distribution, and X-ray diffraction. The filtration loss reduction mechanism showed that degraded nano PM- DAD intercalated between smectite clay minerals, creating electrostatic attraction and hydrogen bonds with the smectite surface, thereby facilitating the formation of a dense filter cake This research not only presents a novel approach for the utilization of pullulan but also offers a new path for controlling high-temperature filtration in water-based drilling fluids.

In the context of drilling operations, the study investigated the ability of a combination of rigid mineral particles and composite plugging agents to seal simulated cracks effectively. The study used a neural network model to predict the outcomes of experiments using this combination, based on data collected during the research. Initially, a backpropagation (BP) neural network was used to establish the prediction model, which was later optimized using the particle swarm optimization (PSO) algorithm to improve its accuracy, stability, and learning abilities. As a result, the optimized prediction model was found to be capable of providing accurate and compliant drilling plugging formulas quickly. This feature helped guide targeted formula experiments and significantly reduced experimental time and costs. In five practices in a well area in the southern Sichuan region of China, the application success rate was as high as 60%, and the time spent on plugging was reduced by an average of 36%. Overall, this study contributes to the development of effective and efficient drilling techniques, which are essential in the exploration and production of hydrocarbon resources.

With the development of deep and ultra-deep wells, there is a need to enhance the rheological and filtration properties of water-based drilling fluids under high temperature and salinity conditions. In this study, maltodextrin polymer nanospheres (MDPN) were synthesized through cross-linking maltodextrin and methylene bisacrylamide (MBA) via inverse emulsion polymerization. Then, the polymer MDPN-DAN was synthesized via aqueous solution polymerization, using maltodextrin polymer nanospheres, N, N-dimethylacrylamide (DMAA), 2-acrylamide-2-methylpropanesulfonic acid (AMPS), and N-vinylpyrrolidone (NVP) as raw materials. Structural characterization confirmed the successful synthesis of the polymer MDPM-DAN, with a median particle size of 234.4 nm. Thermogravimetric analysis revealed a thermal decomposition temperature of 242 degrees C for MDPM-DAN. This polymer demonstrated excellent settling stability at 220 degrees C in high-temperature and weakly alkaline environments. Rheological assessments demonstrated a 754 % enhancement in the drilling fluid's rheological properties when MDPM-DAN was added compared to the base mud. MDPM-DAN demonstrated significant reduction in filtration loss, with polymer mud aged at 220 degrees C showing only 5.6 mL of loss, and polymer mud aged at 220 degrees C with 15 wt% NaCl exhibiting 8.9 mL loss. The filtration loss reduction mechanism elucidated that MDPM-DAN could adsorb onto bentonite particles via hydrogen bonds, while nanoparticles filled the micropores of the filter cake, promoting the formation of a dense filter cake. Furthermore, plugging experiments showcased MDPM-DAN's ability to block nano-pore throats, with the molecular chain's amide groups reinforcing the plugging through hydrogen bonding with rocks, while bentonite coats the micro-pore throats.

The preparation of true shale cores is limited by the characteristics of shale formations, such as the development of bedding and micro-fractures, poor cementation, and fragility. Artificial cores cannot meet the requirements of shale at the nanometer scale and are not representative. Existing plugging evaluation methods have problems such as cumbersome steps, long time consumption, and low evaluation accuracy. Therefore, this paper proposes a shale plugging evaluation method based on the simulation of “thick mud cakes”. This method analyzes the effects of factors such as bentonite dosage, type and dosage of treatment agent, barite content and particle size distribution on mud cake parameters through approximation experiments, establishes a standard slurry formula for “thick mud cakes”, and prepares a standard “thick mud cake” with a thickness of 10.03 mm and a permeability of 4.79·10 -4 mD to evaluate the plugging effect by the reduction rate of permeability. Based on this method, four plugging agents were selected and combined to obtain the best compound plugging agent. The drilling fluid system plugging evaluation was carried out on both the standard “thick mud cake” and thin mud cake, and the microscopic plugging mechanism of shale was analyzed. The results show that this method is simple to operate, has good reproducibility and high accuracy in plugging evaluation results, and has strong application potential.

Shale reservoirs are characterized by the presence of nano-micron pores in abundance, easy breakage due to bedding development, and difficulty in preparing true core samples. Therefore, 3D reconstruction of digital cores has become an important means of studying the microstructure features of shale. Currently, for shale matrix of dense reservoirs, existing deep learning-based reconstruction methods suffer from high costs and low accuracy, mainly due to the insufficient extraction capability of the networks for nano-micron pore features and low core resolution during reconstruction. To accurately predict the nano-micron scale pore structure of shale, we propose a shale 3D reconstruction method based on context-aware generative adversarial networks and high-resolution optical flow estimation (COFRnet-3DWGAN). This method optimizes the 3DWGAN(Wasserstein GAN) and high-resolution optical flow estimation networks by incorporating context-awareness, enhances the feature extraction capability of the networks to improve the learning degree of core nano-micron pores, and optimizes the core resolution by increasing the resolution of optical flow between core sequence images, thereby improving the accuracy of core reconstruction. The results show that, compared with WGAN, the proposed method is closer to the true core in terms of porous media morphological functions, porosity and permeability distribution, and pore structure parameters, indicating that this method has certain advantages in improving the accuracy of shale reconstruction.

The hydration of clay minerals in shale is one of the main causes of borewall instability. Efficient shale hydration inhibitors require strong interactions between the inhibitor and the mineral surface, such as van der Waals forces, static electricity, hydrogen bonds, and even the formation of chemical bonds, which can significantly reduce the crystal layer spacing of clay minerals. The selection of main functional group of inhibitor plays a decisive role in the performance of inhibitor. The density functional theory method based on quantum mechanics can simulate and calculate the interaction between inhibitor and montmorillonite (001) plane, and study its electronic structure and properties at the atomic level. The adsorption of C 2 H 5 –NH 2 , C 2 H 5 –OH, C 2 H 5 –OCH 3 , C 2 H 5 –CHO and C 2 H 5 –COCH 3 on Montmorillonite (001) was calculated by density functional simulation. The adsorption of inhibitor functional groups on montmorillonite (001) layer was studied comprehensively from the aspects of adsorption configuration, adsorption energy, charge population, frontier orbit and differential electron density distribution. According to this study, the primary amine group is suitable as the main functional group of hydration inhibitor. Meanwhile, this paper provides theoretical support for the development of efficient surface hydration inhibitors..

With the development of deep formations, high temperature and high salinity seriously affect the rheology and filtration performance of water-based drilling fluids. Therefore, in this study, a network-structured polymer (DSD-beta-CD) with low viscosity effect was synthesized using beta-cyclodextrin (beta-CD) as the backbone and N,N-dimethylacrylamide (DMAA), sodium p-styrene sulfonate (SSS), and dimethyl diallyl ammonium chloride (DMDAAC) as monomers. The polymer was analyzed by transmission electron microscope, Fourier transform infrared spectrum, nuclear magnetic resonance, and thermogravimetric analysis. The filtrate reducer in this study showed excellent temperature and salt resistance, the filtration loss of the water-based drilling fluid containing 3.5% DSD-beta-CD and 18% NaCl was 5.1 mL after hot rolling at 220 degrees C for 16 h. Additionally, its viscosity was 0.2 mPa s higher than that of the water-based drilling fluid with 18% NaCl, showing an excellent low viscosity effect. The filtration loss reduction mechanism of DSD-beta-CD was investigated by viscosity analysis, mud cake analysis, particle size distribution, hydration swelling of bentonite, and Zeta potential. The results showed that DSD-beta-CD could be adsorbed on the surface of bentonite particles through hydrogen bonds and ionic bonds, which increased the dispersion of bentonite particle and the compactness of the mud cake, thus reducing the filtration loss.

In this study, corn starch/acrylic acid/ itaconic acid (CS/AA/IA) hydrogel was prepared by solution polymerization, and then alkaline washed with sodium hydroxide solution to form corn starch/acrylic acid/ itaconic acid (CS/AA/IA) ion exchange hydrogel for the adsorption of copper and lead ions in aqueous solution. The structure and morphology of the hydrogel were characterized by Fourier transform infrared, X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy. The effects of contact time, initial concentration, temperature, pH, coexisting ions and different water types on the adsorption of Pb2+ and Cu2+ were analyzed by batch adsorption experiments. The CS/AA/IA ion exchange hydrogel reached adsorption equilibrium within 40 min. The maximum adsorption capacities of Pb2+ and Cu2+ fitted by the Langmuir isothermal adsorption model were 869.56 mg/g and 699.31 mg/g, respectively. After five adsorption-desorption cycles, the adsorption capacity of the hydrogel for Pb2+ and Cu2+ remained at 95%. The synthesis method maximized the conversion of -COOH in the hydrogel into the active group -COONa, forming a highly efficient adsorption hydrogel with ion exchange as the main effect. The CS/AA/IA ion exchange hydrogel exhibits high adsorption capacity, fast adsorption efficiency and remarkable regeneration property, and shows potential applications in the field of water treatment.

Shale formations with high levels of microfracture development are prone to problems such as hydration expansion and pressure transmission, which lead to wellbore collapse. At present, it is difficult for plugging materials in oil-based drilling fluids to simultaneously ensure the rheological properties of the drilling fluids and their adaptability to leakage channels of different sizes. Therefore, in order to improve the plugging ability of oil-based drilling fluids, plug microfractures, improve the stability of the well wall, and prevent wellbore collapse, polymer microspheres in a water-in-oil emulsion were synthesized using acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-vinyl-2-pyrrolidone, and N-(hydroxymethyl)acrylamide as monomers. These microspheres did not affect the rheological properties of drilling fluids and effectively sealed microfractures of all sizes. The results of structural characterization and performance tests showed that the particle size of the microspheres was about 500 nm, and the high-temperature high-pressure filtration loss after aging at 150 °C was 6.8 mL. The filtration loss in a sand tray with a pore size of 10 μm using a plugging agent dosage of 3% was only 5.5 mL, which was significant for plugging microcracks with widths of 20–60 μm, and the reduction in the filtration loss exceeded 95%.

针对超低孔超低渗页岩地层的井壁失稳问题,以延长组长7段页岩为参考对象,采用X射线衍射、渗透率、孔隙度、比表面积、平均孔径测定和扫描电子显微镜等手段,分析了矿物组分、岩性特征,提出了页岩井壁维稳思路.借助模拟"标准厚泥饼"封堵评价方法,对ZD-1、JB53、EP-2和ZD-3等封堵剂最佳加量及其复配的封堵效果进行评价,优选得到了高效封堵的复配封堵剂SPA-1.在延长页岩用水基甲酸钾钻井液体系中加入4.0％SPA-1后,其流变性易于控制且渗透率降低率高达94.20％,作用前后的模拟岩芯电镜图像进一步验证了其封堵效果,并分析了封堵剂封堵作用机理.结果表明,SPA-1集合理的粒度级配和刚柔性粒子协同作用可以实现有效封堵,有利于延长组长7段页岩井壁稳定.

Daji block is an important arear of producing and energy in Lifen block of coalbed gas. There are the natural leak-causing crack, water in the formation, narrow security density window, serious leakage and poor plugging in this area. In order to solve the problems, this paper adopted the compound gel plugging technology, which has the advantages of both supramolecular organic gel and inorganic gel, to prevent leakage in this well area. Laboratory tests show that the safe construction time of the composite gel can be controlled within 1-1.5 hours, and the pressure bearing capacity of cracks of 4.0 × 3.5 mm and 3.0 × 2.5 mm can respectively reach 3.3 and 4.5 MPa. It has strong cementing ability to rock particles, and the pressure bearing capacity of 14cm squeezed into the 6-8 mesh sand filling pipe can be 5.6 MPa. Field application show that the special gel technology have the characteristics of easy pump injection and simple construction as well as improve the plugging effect of Daji block.

The development of shale gas reservoirs with water-based drilling fluids is complicated by the problem of clay mineral hydration. The method of molecular simulation is widely used in many research fields, in both humanitarian and material sciences. In this paper, based on the previously published studies, the authors propose a comprehensive review of molecular simulation of inhibiting the surface hydration swelling of clay minerals. Swelling characteristics and the adsorption properties of clay minerals are reviewed and discussed. The results can be useful for future development of the MD (molecular dynamics) simulation method and its application in studies of inhibition of the surface hydration swelling in clay minerals.

A series of sulfonated lignin (SL) samples modified with a silane coupling agent (Si–SL) was investigated as a biodegradable shale inhibitor for water-based drilling fluid (WBDF). Cutting dispersion, linear swelling, bentonite inhibition, and mud ball tests were used to evaluate the inhibition performance of the Si–SL series of and compared with conventional shale inhibitors including potassium formate (HCOOK), polyethylene alycol (PEA), Ultrahib polymer, and polyacrylamide potassium salt (K-PAM). The results showed that the inhibition performance of a series of Si–SL was similar to that of Ultrahib and was significantly better than that of HCOOK, PEA and K-PAM at normal temperature. In addition, compared with other inhibitors, Si–SL showed optimal temperature resistance. The inhibition mechanism of Si–SL was studied by particle distribution, rock compressive strength measurement, shale micro-fracture propagation synthesis, X-ray diffraction (XRD) measurement, adsorption measurement, contact angle measurement, scanning electron microscopy (SEM) observation and atomic force microscopy observation. At high temperature, Si–SL can be strongly adsorbed on the surface of clay particles, while phenyl in molecular chain of Si–SL is conducive to improving the temperature resistance and reducing the hydrophilicity of the surface of clay particles, thus effectively preventing the migration of water molecules to the clay layer. More importantly, through biotoxicity and biodegradability test, the results showed that Si–SL had no toxicity and was easy to be biodegraded. In field application of Bei 213-21HF well, the Si–SL effectively inhibits the hydration of water-sensitive cuttings and maintains the wellbore stability of the shale formation, providing a guarantee for safe and fast drilling.

In this study, a desulfonated hybrid organic/inorganic fluid loss agent resistant to high temperatures is synthesized by using free-radical copolymerization. The fluid loss agent consists of the organic monomer acrylamide (AM), N-vinylpyrrolidone (NVP), dimethyl diallyl ammonium chloride (DMDAAC), and the inorganic monomer KH570 modified by nano-silica (M-SiO2). A field emission transmission electron microscope, an infrared spectrometer, and a thermogravimetric analyzer are used to examine the morphology and structure of the fluid loss agent. The results show that the inorganic nanoparticles and organic polymers are successfully grafted, and the resulting “core-shell” structure is connected by molecular chains. When 2% wt of the synthetic fluid loss additive E(AND-SiO2) is added to the base slurry, the normal-pressure fluid loss (FLAPI) and high-temperature, high-pressure fluid loss (FLHTHP) of the slurry are determined by the aging tests at 150, 160, 170, 180, 190, and 200°C for 16 hours. The results show that when the temperature is 180°C, FLAPI is 6.4 mL, FLHTHP is 28 mL, and temperature resistance is good. The biological toxicity and biodegradability tests show that the fluid loss control agent does not only effectively reduce the fluid loss, but also easily degrades, making it an environmentally-friendly treatment agent.

为了提升"油气井工作液案例"硕士课程教学效果,文章首先阐述了"交互—探究"教学模式的理论基础,然后从构建原则和构建流程两个方面论述了"油气井工作液案例"硕士课程"交互—探究"教学模式的构建.