Search Results (152)

The plugging of fractured gas reservoirs with severe lost circulation during oil and gas drilling and production has long been challenged by technical issues such as low plugging strength and short effective duration. This paper reports the preparation of a high-strength supramolecular gel plugging agent via micellar copolymerization based on the synergistic effects of hydrophobic association and hydrogen bonding. Systematic optimization determined the optimal synthesis formula: acrylamide (AM) 12%, 2-acrylamido-2-methylpropanesulfonic acid (AMPS) 2%, stearyl methacrylate (SMA) 0.4%, sodium dodecyl sulfate (SDS) 1.5%, and potassium persulfate 0.3%, with a reaction temperature of 60 °C. Performance evaluations revealed that the gel possesses a controllable gelation time (120 min) and excellent viscoelastic recovery properties. At a compressive strain of 87%, the compressive stress reached 1.43 MPa while maintaining structural integrity. Swelling behavior analysis indicated that the gel follows a non-Fickian diffusion mechanism, with its swelling process governed by the synergistic interplay of water molecule diffusion and polymer network relaxation. Core plugging experiments demonstrated that the gel achieved plugging efficiencies exceeding 95% for cores with permeabilities ranging from 0.18 to 0.90 μm², with a maximum breakthrough pressure gradient of up to 11.48 MPa/m. These results highlight the gel’s efficient and broad-spectrum plugging capability for fractured lost circulation zones. This preliminary study provides experimental foundations for the material design and performance optimization of supramolecular gel-based long-lasting plugging agents for severe lost circulation gas reservoirs, and further field-scale validation is required for engineering application. Full article

Lost circulation remains a persistent and costly challenge in drilling operations for oil, gas, and geothermal energy systems, particularly when wide fractures and cavernous formations are encountered. Although a wide range of lost circulation materials (LCMs) is commercially available, multiple laboratory studies report that many conventional products are unable to effectively seal fractures of approximately 5 mm width under controlled conditions. In contrast, recent investigations of shape memory polymer (SMP)-based LCMs have demonstrated successful sealing of fractures up to approximately 12 mm in width. This review examines recent advances in SMP-based LCMs as an emerging class of smart materials capable of overcoming geometric and operational constraints associated with drilling equipment, particularly bottom-hole assembly (BHA) components. Through thermomechanical programming, these materials are transformed into compact temporary shapes suitable for seamless circulation and are subsequently triggered by reservoir temperatures to recover permanent geometries up to an order of magnitude larger. Upon activation, these discrete elements function collectively as a hierarchical, jammed system. The resulting multiscale networks—comprising ladder-shaped elements, interwoven fibers, and granular particles—bridge large apertures, enhance mechanical interlocking, and achieve superior hydraulic isolation. Full article

Background: Influenza B virus (IBV) undergoes continuous genetic mutations that can affect vaccine effectiveness and immune evasion. Although considerable research on IBV epidemiology exists globally, understanding of its genetic behavior in Saudi Arabia remains limited. This study characterized the molecular epidemiology of IBV in Riyadh, Saudi Arabia, during the 2024–2025 influenza season and evaluated compatibility with the current vaccine strain. Methods: Nasopharyngeal samples (n = 363) were collected from individuals presenting with influenza-like illness at King Khalid University Hospital in Riyadh. Detection and subtyping of IBV were performed using RT-PCR. Complete sequencing of the hemagglutinin (HA) and neuraminidase (NA) genes was conducted on confirmed IBV isolates (n = 7), followed by phylogenetic analysis, amino acid substitution mapping, and glycosylation site prediction. Results: Of the 363 samples analyzed, 68 (18.7%) tested positive for IBV, with the majority occurring in adult females aged 15–64 years. Phylogenetic analysis revealed that all seven IBV isolates belonged to the Victoria lineage under subclade V1A.3a.2, corresponding to the current vaccine strain and strains from the 2022–2023 epidemic season. However, molecular analysis identified two substitutions (D129N and D197E) located in antigenic loop-150 and 190-helix, respectively, in the HA polypeptide that distinguished our strains from vaccine strain B/Austria/1359417/2021. Importantly, the N-glycosylation site at position 169 (NKT), which was present in B/Riyadh/1/2010, has been lost in the IBV strains circulating during 2020–2025. Conclusions: While phylogenetic clade compatibility indicates potential vaccine efficacy, the identified amino acid variations and loss of the glycosylation site underscore the necessity for ongoing molecular surveillance to monitor antigenic changes and evaluate vaccine effectiveness within the Saudi Arabian population. Full article

Lost circulation is a significant challenge in drilling operations, leading to fluid losses, increased non-productive time, and well instability. This paper develops a predictive model to quantify lost circulation in the Al Jeribe Formation in the Al-Omar field, one of the largest oilfields in the Middle East. Lost circulation is especially prevalent when drilling through the Al Jeribe formation due to the presence of vugs and caves. However, current models for predicting lost circulation often suffer from limited accuracy and efficiency due to the complexity of geological formations and the variability of drilling conditions, leading to unreliable predictions in challenging environments. This research aims to overcome these limitations by developing a more accurate and efficient predictive model tailored to the Al Jeribe Formation, providing valuable insights to mitigate fluid loss and improve drilling efficiency. This paper introduces a novel predictive model for lost circulation in the Al Jeribe Formation, utilizing artificial neural networks (ANNs) trained on extensive field data from over 100 wells. The model incorporates key drilling parameters such as mud weight (MW), yield point (Yp), equivalent circulation density (ECD), rate of penetration (ROP), revolutions per minute (RPM), strokes per minute (SPM), Plastic viscosity (PV), and weight on bit (WOB) as input parameters. The ANN achieved excellent predictive performance, with Training R² = 0.99 and Testing R² = 0.99. Error metrics also confirmed strong generalization, with RMSE = 1.70% (training) and 1.40% (testing), and AAPE = 11.0% (training) and 10.2% (testing). In addition, the model identified the most critical parameters influencing lost circulation and provided optimized parameter ranges to mitigate fluid loss during drilling operations. This study focuses on lost circulation prediction in the Al Jeribe Formation, identifying key drilling parameters and providing optimized ranges to reduce losses and improve wellbore stability. It offers insights not covered in previous research, specifically targeting the Al Jeribe Formation. The model predicts lost circulation and suggests practical adjustments to drilling parameter values. The findings are expected to enhance drilling efficiency and minimize downtime in the Al-Omar field. This methodology can also be applied to similar geological formations worldwide to reduce lost circulation in oil fields. Full article

Severe fluid loss in fractured, depleted reservoirs usually defeat conventional water-based drilling fluids (WBDFs), and rigid lost-circulation materials (LCMs) struggle to form durable, conformal seals. We report an eco-oriented colloidal gas aphron (CGA) fluid built from a nanostructured corn biopolymer (NCBP) and a biodegradable peanut-oil-derived surfactant, benchmarked against a reference fluid (RF) and aphron-only baselines (aphron based fluid, ABF). NCBP, produced by ball milling, was confirmed nanostructured by x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), electron and atomic microscopies. Performance was evaluated from 25 to 90 °C for rheology, aphron stability and filtration at low temperature and low pressure (LTLP) of 100 psi and 25 °C, with post-test mud cake imaging. The optimized formulation, NCBP-2, showed stronger shear-thinning and higher gel strengths with heat, sustained stable and uniform aphrons for at least 120 min with foam persistence beyond 24 h, and delivered 3.0 mL filtrate with a 0.8 mm mud cake. These outcomes correspond to 60% less filtrate and approximately 73% thinner mud cakes than RF (7.5 mL; 3.0 mm), and about 14% and 33% improvements over the best ABF (3.5 mL; 1.2 mm). Micrographs revealed denser, finer-pored mud cakes, consistent with a mechanism in which deformable aphrons bridge micro-fractures while nano-scale polymeric fillers tighten the mud cake network. The results demonstrate decisive loss-control gains with temperature-tolerant rheology, supporting bio-based CGA fluids for depleted and fractured formations. Full article

Frequent drilling fluid lost circulation in the Kuqa foreland area of the Tarim Oilfield severely constrains drilling efficiency and safety. The complex formation structures and diverse lost circulation types in this region are compounded by a lack of systematic classification in existing studies and weak correlation between mechanism analysis and field plugging measures, leading to a deficiency in quantitative decision-making for lost circulation prevention and control. Based on lithology analysis, loss zone pressure differential calculation, well log interpretation, and core observations, this study establishes an integrated “formation–lithology–pressure” diagnostic and classification method for lost circulation. A systematic classification framework comprising five types of lost circulation channels and mechanisms was developed. Based on this, the dominant lost circulation types and characteristics of three typical vertical formations in the Kuqa foreland were clarified: ① The supra-salt sandy conglomerate formations (e.g., Q1x, N2k) are dominated by permeability loss, where the loss rate (V) and bottomhole pressure differential (ΔP) exhibit a strong positive correlation (V ∝ ΔP). On-site application of graded bridging plugging formulations achieved a first-attempt success rate of ≥90%. ② The salt–gypsum formations (E1-2km) are primarily characterized by induced fracture loss, with a weak correlation between V and ΔP and dynamic fracture opening/closing behavior. Conventional rigid plugging materials showed limited effectiveness, resulting in a first-attempt success rate of <50%. ③ The K1bs formation is dominated by vertically developed natural fracture loss, where V and ΔP also demonstrate a strong positive correlation. In a specific Keshen block, a power-law relationship between the fracture aperture (W) and loss rate was established (W = 0.26·V^0.62, R² = 0.98), providing a basis for predicting fracture aperture and optimizing plugging formulations, with a plugging success rate of ≥80%. The classification system and quantitative criteria developed in this study effectively link lost circulation mechanisms, dynamic characteristics, and engineering countermeasures, offering theoretical support and a decision-making framework for optimizing lost circulation prevention and control measures and improving success rates in the Kuqa foreland area. Full article

Lost Circulation (LC) is one of the most common and high-risk complex situations encountered during drilling operations, posing a serious threat to the safe extraction and economic viability of oil and gas resources. Traditional wellbore leakage detection methods based on human experience often suffer from delays and uncertainties, making it difficult to meet real-time warning requirements under complex geological conditions. This paper proposes an LC warning method that combines a physical model with a combination of neural networks (Crested Porcupine Optimizer (CPO)–Long Short-Term Memory (LSTM)–Random Forest (RF)). The physical model utilises changes in mud pit volume, inlet–outlet flow rate differences, and riser pressure to construct interpretable event labels, thereby enhancing the physical plausibility of prediction results. The deep learning component employs LSTM networks to extract temporal features and RF for non-linear discrimination and introduces the CPO algorithm for feature selection and hyperparameter optimisation, thereby enhancing the model’s stability and generalisation capability. Validation using actual field data from the western Bohai Bay oilfield demonstrates that the proposed method outperforms traditional models in accuracy, precision, recall, and F1-score. It also offers a significant improvement in early warning time, detecting potential leakage about 17 min before traditional methods. These results highlight the effectiveness of the approach in managing risks during drilling operations. Full article

During the drilling process of 10,000 m deep wells, loss zones face complex environments with ultra-high temperatures and pressures. Traditional bridging plugging materials exhibit insufficient temperature resistance and tend to carbonize under downhole high-temperature conditions, leading to recurrent loss. To address the technical challenges of drilling fluid loss in ultra-high-temperature formations of 10,000 m deep wells, experimental research was conducted to evaluate the properties of plugging materials resistant to 240 °C. Rigid particles, elastic particles, flaky materials, and fiber materials resistant to 240 °C were optimized. An experimental evaluation method for ultra-high-temperature dense pressure-bearing loss prevention and plugging formulations was established. The ultra-high-temperature while-drilling leak prevention formulation was optimized through sand disk plugging experiments. Millimeter-scale fracture plugging simulation experiments optimized ultra-high-temperature stop-drilling plugging formulations for different fracture apertures, achieving a bearing capacity of 15 MPa within 1–5 mm fracture apertures. Through the synergistic effects of various loss prevention materials, a reinforced force chain network structure forming a dense pressure-bearing plugging layer was achieved under 240 °C high-temperature conditions. This research provides material and system support for the solving drilling fluid loss challenges in high-temperature formations of 10,000 m ultra-deep wells. Full article

This paper synthesizes lessons learned from drilling a CO₂-storage stratigraphic well in the San Juan Basin (New Mexico, USA) to clarify drivers of operational incidents and to inform future well planning. A literature review of regional drilling problems was combined with pre-drill engineering based on offset-well history and a geomechanical model, including casing, cementing, and hydraulics designs developed in commercial software; these designs were compared with field execution to extract incident-specific lessons. The most frequent problems observed are lost circulation, stuck pipe, and poor control of drilling parameters, consistent with complex lithology and reservoir pressure depletion that reduces fracture pressure below anticipated values. Based on the lessons learned, three mitigations are proposed as follows: (1) update the geomechanical model with the latest pore, fracture pressure estimates; (2) apply underbalanced drilling using nitrified mud by injecting nitrogen through a parasite string while drilling intermediate and production sections; and (3) maintain operating limits (weight on bit < 44.5 kN, top-drive rotation < 45 rpm, and pump rate < 1.32 m³/min) to improve fluid returns through low-fracture-pressure intervals. Simulation results support the applicability of the proposed solutions. Full article

Lost circulation in oil-based drilling fluids (OBDFs) remains difficult to mitigate because particulate lost circulation materials depend on bridging/packing and gel systems for aqueous media often lack OBDF compatibility and controllable in situ sealing. A dual-precursor oil–water biphasic metal–organic supramolecular gel enables rapid in situ sealing in OBDF loss zones. The optimized formulation uses an oil-phase to aqueous gelling-solution volume ratio of 10:3, with 2.0 wt% Span 85, 12.5 wt% TXP-4, and 5.0 wt% NaAlO₂. Apparent-viscosity measurements and ATR–FTIR analysis were used to evaluate the effects of temperature, time, pH, and shear on MOSG gelation. Furthermore, the structural characteristics and performances of MOSGs were systematically investigated by combining microstructural characterization, thermogravimetric analysis, rheological tests, simulated fracture-plugging experiments, and anti-shear evaluations. The results indicate that elevated temperatures (30–70 °C) and mildly alkaline conditions in the aqueous gelling solution (pH ≈ 8.10–8.30) promote P–O–Al coordination and strengthen hydrogen bonding, thereby facilitating the formation of a three-dimensional network. In contrast, strong shear disrupts the nascent network and delays gelation. The optimized MOSGs rapidly exhibit pronounced viscoelasticity and thermal resistance (~193 °C); under high shear (380 rpm), the viscosity retention exceeds 60% and the viscosity recovery exceeds 70%. In plugging tests, MOSG forms a dense sealing layer, achieving a pressure-bearing gradient of 2.27 MPa/m in simulated permeable formations and markedly improving the fracture pressure-bearing capacity in simulated fractured formations. Full article

During deepwater drilling operations in the Baiyun block of the eastern South China Sea, high-temperature and high-pressure formation leakage was frequently encountered. Traditional plugging materials lacked adequate stability under these conditions and failed to establish reliable plugs. As the development of the Baiyun Block progressed, it was found that the formation temperature at the BY5 area well reached 182.2 °C at a depth of 4527 m. At a depth of 5206 m, the bottom-hole temperature of the well increased to 223.81 °C, and the pressure rose to 10 MPa. An urgent need has emerged to develop a plugging system capable of operating stably under high-temperature and high-pressure conditions to enhance the safety and success rate of deepwater drilling. In this study, a high-temperature-resistant polymer for controlling leakage rate, an inorganic pressure-bearing particulate material with supporting capability, and a gel that gradually solidifies under high-temperature conditions were developed. Through systematic optimization, a synergistic plugging system was established. Laboratory evaluations demonstrated that the system maintained favorable fluidity and structural integrity under high-temperature and high-pressure conditions, rapidly constructed stable plugging layers across fractures of varying widths, and withstood high differential pressures while resisting backflow-induced erosion. The results indicate that the system exhibits significant plugging performance and strong potential for engineering application, providing reliable technical support for deepwater oil and gas development. Full article

Deep and ultra-deep drilling operations commonly encounter fractured and fracture-vuggy formations, where weak wellbore strength and well-developed fracture networks lead to frequent lost circulation, presenting a key challenge to safe and efficient drilling. Existing diagnostic practices mostly rely on drilling fluid loss dynamic models of single fractures or simplified discrete fractures to invert fracture geometry, which cannot capture the spatiotemporal evolution of loss in complex fracture networks, resulting in limited inversion accuracy and a lack of quantitative, fracture-network-based loss-dynamics support for bridge-plugging design. In this study, a geologically realistic wellbore–fracture-network coupled loss dynamic model is constructed to overcome the limitations of single- or simplified-fracture descriptions. Within a unified computational fluid dynamics (CFD) framework, solid–liquid two-phase flow and Herschel–Bulkley rheology are incorporated to quantitatively characterise fracture connectivity. This approach reveals how instantaneous and steady losses are controlled by key geometrical factors, thereby providing a computable physical basis for loss-zone inversion and bridge-plugging design. Validation against experiments shows a maximum relative error of 7.26% in pressure and loss rate, indicating that the model can reasonably reproduce actual loss behaviour. Different encounter positions and node types lead to systematic variations in loss intensity and flow partitioning. Compared with a single fracture, a fracture network significantly amplifies loss intensity through branch-induced capacity enhancement, superposition of shortest paths, and shortening of loss paths. In a typical network, the shortest path accounts for only about 20% of the total length, but contributes 40–55% of the total loss, while extending branch length from 300 mm to 1500 mm reduces the steady loss rate by 40–60%. Correlation analysis shows that the instantaneous loss rate is mainly controlled by the maximum width and height of fractures connected to the wellbore, whereas the steady loss rate has a correlation coefficient of about 0.7 with minimum width and effective path length, and decreases monotonically with the number of connected fractures under a fixed total width, indicating that the shortest path and bottleneck width are the key geometrical factors governing long-term loss in complex fracture networks. This work refines the understanding of fractured-loss dynamics and proposes the concept of coupling hydraulic deviation codes with deep learning to build a mapping model from mud-logging curves to fracture geometrical parameters, thereby providing support for lost-circulation diagnosis and bridge-plugging optimisation in complex fractured formations. Full article

Lost circulation in fractured formations is a common yet challenging technical problem in drilling engineering. Conventional plugging methods often form sealing layers with poor stability and low pressure-bearing capacity. This study developed an efficient composite plugging agent composed of calcite particles (rigid particles), elastic gel particles, and polypropylene fibers. Utilizing a laboratory-scale fracture plugging evaluation apparatus and standard comparative experimental methods, the synergistic plugging effects of different composite systems were investigated. The results indicate that while single rigid particles can form a basic bridging structure, the pressure-bearing capacity of the resulting sealing layer is limited. Single elastic gel particles or fibrous materials struggle to effectively plug fractures of varying widths. Composite use of the plugging agents significantly enhanced the plugging performance, with the rigid/elastic/fiber ternary composite system demonstrating the best results. The optimal formulation (5% calcite particles + 3% elastic gel particles + 2% polypropylene fibers) achieved a plugging pressure-bearing capacity of 13 MPa for 2 mm-wide fractures, with a fluid loss of only 50 mL and temperature resistance up to 180 °C. Furthermore, the composite plugging agent exhibited good compatibility with the drilling fluid system and demonstrated excellent adaptability and plugging performance for fractures with different roughness levels, indicating promising potential for field application. Full article

Severe lost circulation frequently occurs in deep and ultra-deep wells under high-temperature/high-pressure (HPHT) conditions and in fracture-cavity composite loss channels. Conventional lost-circulation materials (LCMs) often fail because of premature loss of mobility, insufficient residence in loss paths, and irreversible failure after solidification. Cement-based sealing systems, owing to their ability to plug large leakage channels and their cost-effectiveness, have become the mainstream solution. To improve their performance under extreme downhole conditions, recent studies have focused on base-cement design, reinforcement phases, and property regulation strategies-including the use of granular/fibrous/nanoscale additives for bridging reinforcement, rheology and thickening control to enhance injectability and residence, and chemical/functional modifiers to improve compactness and durability of the hardened matrix. Significant progress has been achieved in terms of HPHT resistance, densification design, regulation of rheological properties and thickening behavior, and self-healing/responsive sealing functions. However, most existing studies still focus on improving individual properties and lack a cross-scale, holistic design and unified mechanistic perspective for fracture-cavity coupled flow and long-term sealing stability. Distinct from previous reviews that mainly catalogue material types or discuss single-performance optimization, this review is framed by fracture-cavity composite loss channels and long-term sealing requirements under HPHT conditions, systematically synthesizes the material design strategies, reinforcement mechanisms and applicability boundaries of cement-based plugging systems, builds cross-scale linkages among these aspects, and proposes future research directions toward sustainable plugging design. Full article

Background and Objectives: Hyperleukocytosis in acute myeloid leukemia (AML) is life-threatening, often complicated by leukostasis, tumor lysis syndrome (TLS), and disseminated intravascular coagulation (DIC), with very high early mortality. Leukapheresis (LA) can rapidly reduce circulating blast burden, but its effect on survival and prognostic relevance of disease markers remains unclear. Materials and Methods: We retrospectively analyzed 74 adult AML patients with WBC > 100 × 10⁹/L treated at the University Clinical Center of Serbia between 2014 and 2024: 28 received LA plus cytoreduction (LA group), and 46 received cytoreduction alone (non-LA group). We evaluated 15-, 30-, and 90-day mortality and overall survival (OS), and assessed clinical, laboratory, and immunophenotypic predictors using Cox regression, with separate subgroup analyses. Results: Patients in the LA group had significantly higher baseline leukocyte counts and LDH (p = 0.18 and p = 0.024, respectively). Although LA resulted in a median 34% reduction in WBC, there was no statistically significant difference in early mortality: 15-day survival was 68% vs. 76% (HR 0.70, p = 0.423), 30-day survival 50% vs. 65% (HR 0.62, p = 0.197), and 90-day survival 39.3% vs. 41.3% (HR 0.85, p = 0.604). Median OS was similarly poor, about 1 month in the LA group compared to 2 months in the non-LA (HR 0.73). Across all patients, ECOG PS ≥2, elevated LDH, TLS, and DIC were the strongest indicators of early death. In the LA group, elevated LDH and increased peripheral blood (PB) monocyte count predicted 15-day mortality (p = 0.021 and p = 0.031, respectively), but lost significance by day 90. In non-LA patients, CD25 positivity (p = 0.034) and DIC (p = 0.045) predicted 15-day death. By day 90, CD25 expression (p = 0.048) remained prognostic, while PB blast percentage (p = 0.045) and PB monocyte count (p = 0.017) emerged as additional adverse prognostic predictors in the non-LA group. In multivariate analysis, higher PB blast percentage, CD25 positivity, and ECOG PS ≥ 2 independently predicted poorer OS. Conclusions: Although LA did not reduce early mortality in the entire cohort, the loss of prognostic significance of elevated LDH, high PB blast percentage, PB monocyte burden, and CD25 expression in the LA group may suggest that the intervention can attenuate the impact of biologically aggressive disease. Full article