During the high-rate， high-frequency injection-production of salt-cavern compressed air energy storage， gas carries solid particles upward， causing severe erosion to core surface equipment. To minimize the erosion caused by large particles， it is essential to accurately predict the maximum cuttings-carrying diameter during gas production in salt-cavern compressed air energy storage. Based on the dynamics of gas-borne cuttings carrying， a model integrating the incipient-motion theory and the suspension theory was established to predict the maximum cuttings-carrying diameter during gas production of salt-cavern energy storage wells， and it was verified with field data. Through theoretical derivation and multi-factor coupling analysis， the effects of the cuttings density and shape， storage medium， gas production rate， and the distance between the lower end of the injection-production tubing and the residue surface at the cavern bottom （the lower-end distance in brief） on the cuttings-carrying diameter were systematically investigated， and a shape-coefficient table for irregular particles together with a quantitative predictive fitting formula was established. Field verification shows that the model is stable and accurate， with an accuracy of 92.56%. It is indicated that the cuttings density is negatively correlated with the maximum cuttings-carrying diameter. The gas production rate is approximately exponentially and positively correlated with the cuttings-carrying diameter. The lower-end distance， by affecting the gas velocity at the tubing outlet， is positively correlated with the cuttings-carrying diameter. The relative molecular mass and viscosity of the storage medium alter the cuttings-carrying capacity through the fluid drag force. The shape coefficient of irregular cuttings significantly affects the cuttings-carrying diameter. The proposed model can accurately predict the size of produced solid particles and provides theoretical support for the design of injection-production schemes， the selection of surface equipment， and the optimization of operating plans for salt-cavern compressed air energy storage.
Underground gas storage is a major component of compressed air energy storage power plants， and studying the factors affecting the stability of the surrounding rock of caverns in faulted rock masses is of great significance for the stability evaluation of underground structures and for cavern design and operation. However， existing studies mostly focus on a single surrounding rock type， a single operating condition or a single fault parameter， and rely mainly on finite element or empirical models. Based on the finite difference method and combined with structural-plane surveys and in-situ stress measurements， a realistic numerical model was established by incorporating different lateral pressure coefficients， surrounding rock classes and fault locations. The effects of the fault location and distance on the displacement， plastic zone and failure mode of the surrounding rock under different in-situ stress coefficients and rock classes were analyzed， and the effects of joints and faults on cavern stability under operating and seismic conditions were further investigated. The results show that the fault location has the most pronounced effect on the adjacent cavern wall， with the amplification effect being greatest for vertical faults—the maximum displacement around the cavern reaches 2.0864 cm—whereas inclined faults have a relatively small effect and the deformation is not very sensitive to the dip angle. The maximum stress concentration factor varies nonlinearly with the gas storage pressure and is significantly affected by the fault type. The vertical fault model shows the largest reduction in the maximum stress concentration factor， reflecting its strongest disturbance to the stress distribution. Under seismic action， the heterogeneity and slip characteristics of faults significantly amplify the dynamic response of the surrounding rock. The maximum z-direction displacement of the vertical fault model reaches 4.96 cm， and the responses of the inclined fault models are relatively moderate but still 3.4%-5.1% higher than those of intact rock. The research findings are referential for the engineering design of underground gas storage.
After solution mining of salt cavern， the sediment space， formed by the settling of interlayers and insolubles， will cause serious economic losses and resource waste if it cannot be used for energy storage. Although twin-well salt-cavern storage can increase the gas storage capacity， utilization of the sediment space is still at the experimental stage， and its mechanism， injection-production behavior and key influencing factors remain unclear. Accordingly， based on the formation characteristics of the A twin-well salt-cavern storage in China， the structural features of the rock-salt beds and the properties and volume fraction of the sediment space were analyzed. On this basis， a multiphase-flow model of gas injection and brine drainage in twin-well salt-cavern storage was built with computational fluid dynamics software， and the effects of the gas injection rate， permeability and connecting-channel angle on gas injection and brine drainage were investigated. The results show that the sediment space accounts for 55.52%-71.77% of the A twin-well salt cavern and that the gas-storable space in the sediment can reach 10.25%-26.50%， indicating a prominent storage value. Porosity is positively correlated with permeability， and the volume-fraction equation can characterize the geological features. During gas injection and brine drainage， gas floats upward to displace brine； the brine-displacement rate drops sharply after reaching its peak， and the cumulative displaced volume increases rapidly at first and then levels off. A higher gas injection rate corresponds to a higher brine-displacement rate， but the injection rate affects the cumulative displaced volume by only 3.56%. Compared with a 0° channel， a 20° connecting channel prolongs the gas-production time by 550 s and increases the displaced brine volume by 43.91%， so an inclined connecting channel is recommended. Verification by a 12.36×104 m3 compressed air energy storage project in Hubei Province shows that a high-injection， low-displacement mode of 100 m3/h has achieved a displaced brine volume of 40×104 m3， confirming that the sediment space can be reused. The research findings provide a theoretical basis for optimizing injection-production engineering in twin-well salt-cavern storage.
The power generation of a well-site photovoltaic （PV） power station is closely related to its revenue， and its generating capacity depends on many factors， such as the station design， module performance and system condition. A scientific evaluation of PV station efficiency is therefore essential for station development. For the first batch of PV power stations built in the Changqing Oilfield， a distributed PV performance test scheme was designed. The generation efficiency of the distributed PV stations was comprehensively evaluated from the series-parallel mismatch loss， AC/DC line losses， inverter efficiency， system efficiency and infrared thermal imaging scans of the arrays， and optimization suggestions were proposed accordingly. The results show that the series-parallel mismatch loss of the target stations is small， and the strings with relatively large mismatch loss exhibit clear differences in electrical performance. The AC and DC line losses are both within the standard limits and have little influence on the system efficiency. The PV system efficiency first increases and then decreases over time； inverter over-sizing loss and shading are the main causes of system-efficiency loss， and higher system efficiency is observed at low irradiance. The well-site environment increases the number of hot spots in PV generation， and shortening the grid-connection distance effectively reduces the AC/DC line losses. The research findings provide a reference for the large-scale deployment of intelligent intermittent distributed PV generation at well sites.
By switching the wellhead drilling fluid circulation path， a continuous circulation drilling system can effectively eliminate the circulation interruptions and bottomhole pressure fluctuations caused by frequent pump starts and stops when making or breaking connections， thereby significantly improving drilling safety. The pressure loss characteristics of the main and side circulation lines of the control manifold directly determine the amplitude and duration of the pressure fluctuations during path switching， as well as the total circulation pressure loss. To address the shortcomings of existing continuous circulation system manifolds， including too many elbows and transition sections， undersized drift diameter， and excessive footprint， three principles for structural optimization were proposed： fewer abrupt changes in the flow path， better valve selection， and optimized spatial layout. Accordingly， a novel three-dimensional continuous circulation manifold suitable for offshore platforms was designed. A flow-field pressure loss analysis model of the novel manifold was built and used， together with laboratory tests， to reveal the pressure loss control performance and influencing factors of the novel manifold. The flow-field and transient analyses of the main and side circulation paths of the novel manifold at a flow rate of 2 500 L/min indicate that the large-radius bends， optimized throttle valve and enlarged drift diameter greatly reduce the local vortex intensity， effectively suppress fluid disturbance and pressure fluctuation in the manifold， and reduce the local flow resistance， thereby lowering the flow pressure loss. Compared with the manifold of the existing CCDS-2 continuous circulation system， the main and side circulation paths of the novel manifold demonstrate pressure losses reduced by 64.7% and 55.8% at 2 000 L/min and by 75.5% and 66.4% at 3 500 L/min， respectively. These results meet the dual requirements of offshore continuous circulation operations for compact spatial layout and low frictional pressure loss. The study provides theoretical support for the miniaturized integrated design and pressure loss control of continuous circulation equipment.
