The effects of complex well conditions in shale oil wells on the swelling and tribological properties of high-acrylonitrile stator rubber used in screw pumps were investigated in this study. Tests were conducted considering the combined effects of immersion medium, temperature, and duration. The key parameters measured included mass change rate, volume change rate, hardness, elongation at break, tensile strength, surface micro-morphology of the rubber after thermal expansion and swelling, friction coefficient, and wear quantity. The results indicated that in the actual well fluids, the mass change rate of high-acrylonitrile rubber ranged from −1.08% to 1.29%, with a maximum volume change rate of 2.78%. In diesel oil, the greatest mass change rate of the rubber was 4.68%, and the volume change rate did not exceed ±1%, indicating superior swelling resistance. In both actual well fluids and diesel oil, the maximum decreases in hardness were 8.7% and 9.5%, respectively. Tensile strength and elongation at break decreased with increasing immersion temperature, with elongation at break in 80 °C diesel oil decreasing by over 50%, indicating a significant decline in the tensile properties of the rubber. The average friction coefficient of rubber specimens immersed in actual well fluids at three temperatures, as well as in diesel oil at 25 and 50 °C, decreased compared with the high-acrylonitrile rubber without thermal expansion and swelling. However, the average friction coefficient of rubber specimens immersed in diesel oil at 80 °C increased. The wear quantity of the rubber increased following immersion in both media. Additionally, the friction coefficient and wear quantity of the rubber increased with increasing immersion temperatures. The results of the study can offer valuable insights into assessing the durability of properties in high-acrylonitrile stator rubber under complex well conditions.

Given the friction and drag reduction effects observed in various biological hexagonal structures in nature, a new design was implemented on the rubber surface of the stator of a submersible screw pump. This design featured a multilayer concentric hexagonal groove structure. Furthermore, a composite multilayer hexagonal structure integrating grooves and pits was also developed and applied. This study investigated the influence of groove layer number, groove depth, pit depth, and multilayer hexagonal groove texture arrangement on the rubber surface flow characteristics. Additionally, the pressure field state, the degree of influence on the oil film-bearing capacity, and the biomimetic and hydrodynamic lubrication theories were tested using the finite element analysis method. Tribological experiments were conducted on nanosecond laser-processed rubber textures under simulated liquid lubrication conditions, reflecting actual shale oil well experiments. These experiments aimed to investigate the influence of multilayer hexagonal shape parameters on the tribological characteristics of the stator-rotor friction pair of a submersible screw pump. The results indicated that with a constant overall size, a multilayer hexagonal structure with ~0.1 mm groove depth enhanced the oil film-bearing capacity, providing significant friction and drag reduction. For composite textures, a deeper pit depth within the study area enhanced the oil film-bearing capacity. Furthermore, a gradient arrangement of groove textures featuring wider outer grooves and shallower depth exhibited superior performance in terms of bearing capacity.

Dynamic characteristics of offshore natural gas hydrate (NGH) dissociation will provide the theoretical basis to analyze technical issues of oceanic hydrate exploitation. A mathematical model is developed to simulate offshore NGH dissociation by depressurization in marine sediments. Different phase combination statuses are involved in the process of NGH dissociation by taking ice melting and water freezing into account. The proposed methodology can analyze the processes of hydrate and water phase transitions, decomposition kinetics and thermodynamics, viscosity and permeability, ice-water phase equilibrium, and natural gas and water production. A set of an experimental system is built and consists of one 3-D visual reactor vessel, one isothermal seawater vessel, one natural gas and water separator, and one data acquisition unit. The experiments on offshore NGH dissociation by depressurization in 3-D marine sediments are carried out, and this methodology is validated against the full-scale experimental data measured. The results show that during the prophase, natural gas flow is preceded by water flow into the production wellbore and natural gas occupies more continuous flow channels than water under a large pressure gradient. Then, the natural gas flow rate begins to decline accompanied by an increase of water production. During the second phase, natural gas flow rate decreases slowly because of the decreased temperature of hydrate-bearing formation and low pressure gradient. The lower the intrinsic permeability in marine sediments, the later the water flow rate reaches the peak production. And the space interval of the production wellbore should be enlarged by an increase of the intrinsic permeability. The stable period of natural gas production enhances, and the water flow rate reduces with the increase of bottom-hole pressure in production wellbores. The main reason is the slow offshore NGH dissociation under the low producing pressure and the restriction of heat conductivity under the low temperature.

Accurate load forecasting is crucial to the stable operation of integrated energy systems (IES), which plays a significant role in advancing sustainable development. Addressing the challenge of insufficient prediction accuracy caused by the inherent uncertainty and volatility of load data, this study proposes a multi-energy load forecasting method for IES using an improved VMD-TCN-BiLSTM model. The proposed model consists of optimizing the Variational Mode Decomposition (VMD) parameters through a mathematical model based on minimizing the average permutation entropy (PE). Moreover, load sequences are decomposed into different Intrinsic Mode Functions (IMFs) using VMD, with the optimal number of models determined by the average PE to reduce the non-stationarity of the original sequences. Considering the coupling relationship among electrical, thermal, and cooling loads, the input features of the forecasting model are constructed by combining the IMF set of multi-energy loads with meteorological data and related load information. As a result, a hybrid neural network structure, integrating a Temporal Convolutional Network (TCN) with a Bidirectional Long Short-Term Memory (BiLSTM) network for load prediction is developed. The Sand Cat Swarm Optimization (SCSO) algorithm is employed to obtain the optimal hyper-parameters of the TCN-BiLSTM model. A case analysis is performed using the Arizona State University Tempe campus dataset. The findings demonstrate that the proposed method can outperform six other existing models in terms of Mean Absolute Percentage Error (MAPE) and Coefficient of Determination (R²), verifying its effectiveness and superiority in load forecasting.

The model of hydrodynamic lubrication in the flow field was developed by coupling of hexagonal micro-texture and enclosed groove with a bionic honeycomb structure. The lubrication performance and friction characteristics of the friction pair between the stator and rotor of a screw pump were evaluated on the simulated and experimental results of high acrylonitrile rubber. As the groove depth increased, the cavitation effect and increasing vortex energy losses weakened the friction reduction and wear resistance. An additional bucket-shaped vortex flow was formed beneath the original vortex in the double wedge-shaped overlapping groove, while a new dustpan-shaped divergent flow was formed in the single wedge-shaped boundary groove. Tiny erosion pits were present at the outer edges of the groove bottom after immersion. Slight wear marks were observed on the rubber surface, with fatigue peeling in the texture chamfers, thereby deepening wear marks in some parts of the extended texture region.