Perm National Research Polytechnic University

Transcatheter aortic valve implantation (TAVI) is an innovative minimally invasive procedure designed to replace a damaged or narrowed aortic valve. One of important factor is a device selection, which means variety of stent frame types. Bending stiffness of TAVI stent frame provides an ability to withstand external deformation, when it is implanted in the aortic annulus. Patient-specific manufacturing can solve a problem of patient-device sizing and compatibility. For customized manufacturing it is necessary to find a relation between TAVI implant design and strength to avoid post-operative complications. Nevertheless, studies of relations between structure of TAVI stents and their mechanical performance are rare. Thus, eight stent geometries (a–h) including commercial ones (a, b) and own-developed (c–h) were manufactured by filament fused fabrication. Basing on mechanical tests, features of TAVI stent frames, numerical simulations of stent deployment and bending were carried out. Three-point bending was also performed on manufactured stents. The least average value of bending stiffness was shown by models a, e, f, g (0.92–1.09 kN⋅mm2), while the greatest average value was obtained for c model (5.05 kN⋅mm2). Additionally, correlation analysis was performed. To reach bending stiffness of 6 kN⸱mm2, waist position should be 22.4 mm, parameters vertical and horizontal should be 3.4 and 8.7, respectively. The proposed study can help to choose proper TAVI stent frame design basing on demanding stiffness of aorta to provide accurate short- and long-term performance of the prothesis.

Accurately predicting Flowing Bottom-Hole Pressure (FBHP) is critical for optimizing oil and gas production. Existing predictive methods often rely on oversimplified or complex, yet computationally expensive, models that fail to capture the intrinsic nonlinearities of well dynamics, leading to inaccurate predictions and potential economic losses. This paper introduces a three-layer heterogeneous stacking ensemble model to address the latter challenge. In particular, the key novelty of the developed work is a hierarchical architecture that integrates five distinct Machine Learning (ML) base learners, two meta-learners, and a final super-learner, i.e., an additional meta-model that combines the outputs of the meta-learners to capture complex, non-linear relationships in the data. When evaluated on a field dataset (total dataset samples N=795; test set samples N=199), the proposed Super Learner Stacking model (ST-S) demonstrated superior predictive performance on the independent test set, achieving R-squared (R2) = 0.857±0.006 and Root Mean Squared Error (RMSE) = 146.382±2.806. In addition, the ST-S model outperformed all individual models and simpler stacking ensembles reported in the article. As a result, the developed ST-S model provides a robust, data-driven tool for FBHP prediction, achieving high predictive accuracy without resorting to computationally expensive methods, thereby supporting improved well management and production optimization.

The viscoelastic properties of ultraviolet radiation-curable polymer coatings of optical fibers were studied experimentally and numerically. The test setup was completed, and a series of natural experiments were conducted for an extended temperature range from -110 °C to +120 °C using a dynamic mechanical analyzer (DMA). Discrete dependencies of the complex modulus on temperature and frequency of kinematic loading were obtained. The problem of multiparametric optimization was solved. Defining relations were obtained for protective coating polymers, making it possible to describe the thermomechanical behavior of the glass-forming materials under consideration in a wide temperature range, including relaxation transition. The optimal solution was found for 18 series terms at the selected reference temperature Tr = -70 °C, C1 = 20.036, and C2 = 32.666 for the DeSolite 3471-1-152A material. The optimal solution was found for 60 series terms at the selected reference temperature Tr = 0 °C, C1 = 40,242.2827, and C2 = 267,448.888 for the DeSolite DS-2015 material. The models were verified according to the data of creep experiments. The capabilities of the viscoelastic model were demonstrated by the example of a numerical experiment on free thermal heating/cooling of a Panda-type optical fiber.

The main task when extracting oil from waterflooded reservoirs during late development stages is enhancing the mobility of the remaining reserves. In the context of declining oil export prices, the use of chemical and gas methods for enhancing oil recovery in mature fields is becoming increasingly unprofitable, given their associated technological and economic risks. To improve the efficiency of mature oilfield development, non-stationary (cyclic) waterflooding is an alternative to tertiary methods for enhancing oil recovery. The primary benefit of cyclic waterflooding is its simplicity of implementation and minimal extra costs, which have made this method very appealing in today's market conditions. The relevance of cyclic flooding within the context of this study is underpinned by the prevalence of mature fields in the region, including the asset under investigation. This article presents approaches for planning cyclic waterflooding, using an example of a complex carbonate reservoir from the Tournaisian stage (C1t) oilfield of the Perm Krai, Russia. The novelty of this research lies in the presented laboratory-based studies of the hysteresis of relative phase permeabilities (HRPPs) in "water-oil" systems, which are then used to assess the effectiveness of cyclic waterflooding technology on an updated 3D hydrodynamic model via tNavigator software. Results from the multivariate calculations for cyclic waterflooding are presented, both with and without considering HRPP. The importance of incorporating models with inverse hysteresis loops into commercial simulators for carbonate porous media with mixed types of rock wettability is demonstrated and justified, and directions for future research are proposed. These findings emphasize the need for laboratory studies of carbonate reservoirs in imbibition and drainage modes to constrain the real reservoir processes occurring during cyclic waterflooding. (c) 2025 Sinopec Petroleum Exploration and Protection Research Institute. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Sour gas fields present substantial flow assurance challenges, particularly the rapid formation of gas hydrates that can obstruct pipelines, cause equipment failures, and lead to severe operational losses. The problem is especially critical for sour systems, where H₂S hydrates form more readily and remain stable under milder conditions than their methane counterparts. This study investigated two polyquaternium-based KHIs (PQ-7 and PQ-10), designed to enhance hydrate inhibition in sour gas systems through synergistic physicochemical and molecular mechanisms. In the uninhibited system, hydrate formation initiated rapidly with an induction time of 4.1 h and ΔT of 3.8 °C. PQ-7 demonstrated superior performance even at low dosages: at 1000–5000 ppm, it achieved induction times of 23–24 h and ΔT values exceeding 17 °C. PQ-10 exhibited concentration-dependent inhibition, with significant improvement only at higher dosages (>2500 ppm), where its ΔT reached 16.9 °C. Foaming analyses confirmed that both PQs exhibit low and transient foamability—an operationally desirable trait for offshore and subsea systems where excessive foaming complicates chemical recovery and separation processes. Complementary molecular dynamics (MD) simulations provided atomistic insights into the inhibition mechanisms. PQ-containing systems delayed nucleation onset to approximately 40 ns and exhibited significantly slower hydrate cage accumulation, lower F4 structural order parameters, and attenuated energy transitions. Spatial mapping of water mobility revealed that PQ molecules created “hydrate-free zones” characterized by disordered, highly mobile water, confirming localized disruption of hydrogen-bond networks and steric hindrance near inhibitor molecules. These findings demonstrate that PQ-based KHIs impede both nucleation and growth stages of hydrate formation by modulating interfacial water structuring rather than altering bulk thermodynamics. This work establishes PQ-7 and PQ-10 as promising low-dosage, low-foaming KHIs for sour gas systems. By addressing the challenges posed by H₂S-rich environments, this research contributes to the safe and efficient development of increasingly critical sour gas resources.