Submarine pipelines are a safe and energy-efficient mode of gas transport. However, due to the complex manufacturing process and harsh operating environment, submarine pipelines are subject to fatigue cracks under long-term cyclic loading. A comprehensive and high-precision characterization strategy for submarine pipelines can effectively prevent potential safety hazards and have significant economic and social repercussions. As a matter of fact, pipeline defects cannot be reliably detected with current traditional 2D methods. On the other hand, in ultrasonic testing, cylindrical geometry increases the complexity of the 3D wave field in the submarine pipeline space and significantly influences the accuracy of the detection results. In this paper, we put forward a novel method for 3D ultrasonic image testing that is suitable for cylindrical coordinates. In order to accurately simulate the ultrasonic signal received from pipelines, we generalize the 3D staggered-grid finite-difference method from Cartesian coordinates to cylindrical ones and simulate the full wave field in the 3D pipeline space. Then, signal processing is performed on the ultrasound simulation records, and 3D reverse-time migration imaging of submarine pipeline defects can be effectively achieved using the reverse-time migration method and cross-correlation imaging conditions. The results obtained from simulations and real field data show that the proposed method provides high-quality 3D imaging of defects in pipelines, taking into account multiple scattering and mode conversion information at the bottom of the defects.

Seismic advance detection is a method for detecting complex geological formations in a tunnel face, which is crucial for the safe construction of tunnel projects. During the process of three-dimensional (3D) reverse time migration (RTM) imaging, the wavefield complexity in tunnel space is exacerbated by the cylindrical cavity and the storing and reading of a source wavefield spatiotemporal sequence, which affects the precision of exploration results and the data Input/Output (I/O) consumption. Therefore, we propose an elastic RTM of wavefield reconstruction based on the representation theorem with the equivalent source method in cylindrical coordinates of 3D tunnel space. This method can reduce the demand for storage space exhibited by the source wavefield and lay the foundation for RTM imaging using a higher-precision and larger-size cylindrical coordinates model. To obtain detection results that exhibit more precision and a wider range of detection in tunnel advance detection technology, this study constructs a complicated geological formations model ahead of the tunnel and utilizes this method to perform 3D RTM imaging. The results indicate that the proposed method can effectively realize RTM imaging in cylindrical coordinates for the exploration of complicated geological formations in 3D tunnel space based on the wavefield reconstruction of the representation theorem with equivalent source injection.

Since light propagation in a multimode fiber (MMF) exhibits visually random and complex scattering patterns due to external interference, this study numerically models temperature and curvature through the finite element method in order to understand the complex interactions between the inputs and outputs of an optical fiber under conditions of temperature and curvature interference. The systematic analysis of the fiber’s refractive index and bending loss characteristics determined its critical bending radius to be 15 mm. The temperature speckle atlas is plotted to reflect varying bending radii. An optimal end-to-end residual neural network model capable of automatically extracting highly similar scattering features is proposed and validated for the purpose of identifying temperature and curvature scattering maps of MMFs. The viability of the proposed scheme is tested through numerical simulations and experiments, the results of which demonstrate the effectiveness and robustness of the optimized network model.

Although pressure pipelines serve as a secure and energy-efficient means of transporting oil, gas, and chemicals, they are susceptible to fatigue cracks over extended periods of cyclic loading due to the challenging operational conditions. Their quality and efficiency directly affect the safe operation of the project. Therefore, a thorough and precise characterization approach towards pressure pipelines can proactively mitigate safety risks and yield substantial economic and societal benefits. At present, the current mainstream 2D ultrasound imaging technology faces challenges in fully visualizing the internal defects and topography of pressure pipelines. Reverse time migration (RTM), widely employed in geophysical exploration, has the capability to visualize intricate geological structures. In this paper, we introduced the RTM into the realm of ultrasonic non-destructive testing, and proposed a 3D ultrasonic RTM imaging method for internal defects and sensor settings of pressure pipelines. To accurately simulate the extrapolation of wave field in 3D pressure pipelines, we set the absorbing boundary and double free boundary in cylindrical coordinates. Subsequently, using the 3D ultrasonic RTM approach, we attained higher-precision 3D imaging of internal defects in the pressure pipelines through suppressing imaging artifacts. By comparing and analyzing the imaging results of different sensor settings, the design of the observation system is optimized to provide a basis for the imaging and interpretation of actual data. Both simulations and actual field data demonstrate that our approach delivers top-notch 3D imaging of pipeline defects (with an imaging range accuracy up to 97.85%). This method takes into consideration the complexities of multiple scattering and mode conversions occurring at the base of the defects as well as the optimal sensor settings.

The Bohai Bay Basin is a typical marginal basin with complex internal structures and abundant oil and gas resources, exhibiting unique marine geological characteristics and processes. Based on seismic profile interpretation and balanced cross-section techniques, this paper presents a comprehensive systematic study of the structural combination and tectonic evolution of the Neo-Mesozoic–Cenozoic superimposed basin in the southern Bohai Bay Basin. The research findings indicate that the area exhibits four types of structural properties, including compression, extension, strike-slip, and thrust structures, along with thirteen fundamental styles. Building upon this foundation, research has been conducted on the tectonic evolution and formation processes during the Mesozoic and Cenozoic eras. Based on the effective correlation between hydrocarbon generation and tectonic evolution phases, a three-phase model was proposed as “early anticline-controlled oil accumulation-primary reservoir formation, mid-stage fault adjustment-secondary reservoir formation, late-stage block modification-multiple phase petroleum accumulation”. Our model explains the composite reservoir system in the Neogene–Mesozoic era, characterized by multiple-stage structural oil and gas accumulation, coexistence of primary and secondary hydrocarbon, and various types of oil and gas reservoirs. This study elucidates the controlling effects of structural characteristics and evolution on oil and gas accumulation under marine geological conditions, providing a theoretical basis for the efficient development of oil and gas resources in marginal basins.

The ocean harbors vast potential for oil and gas resources, positioning offshore drilling as a critical approach for future energy exploration. However, high-temperature and high-pressure offshore reservoirs present formidable challenges, as conventional water-based drilling fluids are prone to thermal degradation and rheological instability, leading to wellbore collapse and stuck-pipe incidents. Offshore oil-based drilling fluids (OBDFs), typically water-in-oil emulsions, offer advantages in wellbore stability, lubricity, and contamination resistance, yet their stability under extreme high-temperature conditions remains limited. This study reveals the enhancement of offshore OBDFs performance in harsh conditions by employing nano-SiO₂ to synergistically improve emulsion film stability and non-Newtonian rheological behavior while systematically elucidating the underlying mechanisms. Nano-SiO₂ forms a composite film with emulsifiers, reducing droplet size, enhancing mechanical strength, and increasing thermal stability. Optimal stability was observed at an oil-to-water ratio of 7:3 with 2.5% nano-SiO₂ dispersion and 4.0% emulsifier. Rheological analyses revealed that nano-silica enhances electrostatic repulsion, reduces plastic viscosity, establishes a network structure that increases yield stress, and promotes pronounced shear-thinning behavior. Macroscopic evaluations, including fluid loss, rheological performance, and electrical stability, further confirmed the improved high-temperature stability of offshore OBDFs with nano-SiO₂ at reduced emulsifier concentrations. These findings provide a theoretical basis for optimizing offshore OBDFs formulations and their field performance, offering breakthrough technological support for safe and efficient drilling in ultra-high-temperature offshore reservoirs.