Search Results (6)

This study systematically investigates the gas-tightness evolution of three threaded casing connections (511 straight-thread, TPG2, and BGT2) under extreme downhole temperature–pressure conditions through multi-cycle experiments. A novel cyclic testing protocol was developed to simulate three critical scenarios: 50 °C/21 MPa (low-temperature high-pressure), 350 °C/21 MPa (high temperature and high pressure), and 450 °C/7 MPa (high temperature and low pressure). Quantitative leakage analysis using the ideal gas law revealed significant performance divergence: TPG2 demonstrated superior stability with leakage rates of 0.61% (350 °C/21 MPa) and 0.39% (450 °C/7 MPa), attributed to its barb-type threads and multi-stage sealing design. In contrast, conventional 511 connections showed 2.54% leakage under high-temperature, high-pressure conditions, while domestic BGT2 exhibited intermediate performance (2.46% at 350 °C/21 MPa). The results establish temperature–pressure synergy as the dominant degradation factor, with combined 350 °C/21 MPa conditions causing 300–400% higher leakage than individual extremes. These findings provide critical empirical evidence for optimizing premium connection designs in complex reservoirs, particularly for thermal recovery and ultra-deep applications where sealing integrity determines operational safety and efficiency. Full article

Silk fibroin (SF)-based materials attract significant interest because of their biocompability and great diversity of possible morphologies. One of the approaches to obtain SF materials is the use of an air–water or oil–water interface as a template for protein self-assembly. Surfactants can change the surface properties of adsorbed SF layers by promoting or preventing the formation of SF fiber networks. This study focuses on the influence of two typical ionic surfactants, cationic cetyltrimethylammonium bromide (CTAB) and anionic sodium dodecyl sulfate (SDS), on the dynamic properties of SF layers adsorbed at the air–water interface. The dynamic surface elasticity, surface tension, ellipsometric angle Δ, and the film thickness were measured as a function of the surface age and surfactant concentration. The morphology of the layers was evaluated by atomic force microscopy (AFM). For the adsorption layers of globular proteins, the main effect of the surfactants consists in the protein unfolding at high concentrations and in a decrease in the electrostatic adsorption barrier. In the case of SF layers, CTAB and SDS strongly influence the protein aggregation at the air–water interface. Regardless of the sign of the surfactant charge, its addition to SF solutions results in a decrease in the surface elasticity and the destruction of the ordered structure of protein fibers at concentrations higher than 1 × 10⁻⁴ M. With the further increase in the surfactant concentration, the thread-like aggregates disappear, the packing of thin fibers becomes less tight, a uniform layer disintegrates into separate islands, and finally, the protein is displaced from the interface. Full article

Oil casings and premium threaded connections play vital roles in the oil and gas extraction industry. The present work establishes an integrated modeling framework for the sealability assessment of premium threaded connections which can be easily implemented and employed by engineers. The framework incorporates a part-scale finite element analysis of the make-up process, a micro-scale simulation of the contact behavior, and a mechanism-informed gap flow model. It is found that complete sealing can be achieved when the contact pressure exceeds 1540 MPa for Gaussian rough surfaces presenting a roughness of 1.6 μm. The seal surface fit is revealed to be critical for sealing performance, as it slightly changes the optimum make-up torque (up to 4%) but significantly changes contact pressure (up to 22%). At an optimum make-up torque, the connection with the loosest seal surface tolerance fit is prone to gas leakage when considering an inlet pressure of 110 MPa. The proposed modeling framework can be extended to other types of threaded connections with metal–metal contact sealing. Full article

With green and low-carbon developments in oil fields, an increasing amount of repaired oil tubing is being used as oil and gas transmission pipelines in China. However, due to differences in manufacturing standards between oil tubing and transmission pipelines, there are inevitably some issues during their use. This paper investigates a case of cracking failure in repaired oil tubing used as a gathering and transportation pipeline. The failure occurred after eight months of operation and was characterized by a circumferential crack at the male thread end of the tubing joint. To determine the root cause of the failure, a series of experiments were conducted on the oil tubing. The experiments included visual inspection, chemical composition analysis, mechanical properties testing, hardness testing, metallographic examination, and microstructure analysis. The results revealed that the thread of the cracked tubing was not tightened to the specified position; the connection between the tubing and the coupling was welded in a circumferential direction; and cracks occurred in the heat-affected zone of the weld. Chemical composition, tensile performance, and the Charpy impact of the tubing meet the requirements of API 5CT for P110 material, and no abnormalities were found in the metallographic structure. The microstructure at the weld toe of the fracture is martensite, and the hardness is 476 HV10. Based on the thermal simulation verification test, when the material of the tubing cools from 1200 °C, which is located in the coarse HAZ temperature zone, the base metal transforms into martensite with a little granular bainite, exhibiting its highest hardness value at 371 HV10, which is higher than the allowable hardness for carbon steel and indicates the material has poor weldability. The reasons for the cracking and failure of the tubing are that the P110 repaired tubing has a high carbon equivalent and poor weldability. During the welding process, martensitic structure was formed at the weld toe, and cold cracks appeared in the heat-affected zone, resulting in failure. To avoid the reoccurrence of such failure, recommendations are proposed. Full article

The three-dimensional reconstruction of high-gloss/reflection and low-texture objects (e.g., oil casing threads) is a complex task. In this paper, we present a novel approach that combines convolutional neural networks (CNNs) and multi-layer perception (MLP) with traditional three-dimensional reconstruction methods, thereby enhancing the detection efficiency. Our method utilizes a dataset of 800 samples that includes a variety of thread defects to train a U-net-like model as a three-dimensional reconstructor. Then, an MLP model is proposed to improve the accuracy of the three-dimensional reconstructed thread profile to the level of three-coordinate measurements through a regression analysis. The experimental results demonstrate that the method can effectively detect the black-crested threads of oil casing threads and quantify their proportions in the entire sample for accurate quality assessment. The method is easy to operate and can detect black threads effectively, providing a powerful tool for oil companies to ensure exploration benefits. Full article

A rotational version of the fluid-mechanical sewing machine (FMSM) is investigated experimentally. A thin thread of silicon oil was dispensed at a constant flow rate Q from a height H and fell on a table rotating at an angular speed $\omega$, at a distance R from the axis. In all experimental runs, the values of Q and H were kept constant while the radius R was changed manually after each full rotation. Preliminary results show that the usual stitching patterns ensue as the local linear speed $V=\omega R$ approaches the critical transition speeds seen in the FMSM scenario but with subtle asymmetries introduced by rotational (centrifugal) effects. In some instances, arcs and loops of the traces were noticeably more pronounced when directed outward compared to those pointing toward the axis of rotation. Moreover, we observed stitching patterns not reported before. Overall, the symmetry-breaking features, while clearly visible, were rather subtle. Their morphological characteristics, such as differences in local curvature of traces relative to those in FMSM, are estimated to be below 10% in most cases. Full article