Under the national strategy of carbon peak and carbon neutrality in China,utilizing CO₂ for enhanced oil recovery becomes an important means of CO₂ storage in oilfields. However, there are still challenges in the safe storage and transportation of liquid CO₂,in which gas impurities have a great influence on the thermodynamic properties of liquid CO₂.Seven common gas impurities were determined by the analysis of CO₂ samples obtained in the field,and the changes in physical properties of the CO₂ samples containing impurities were simulated by HYSYS and the molecular dynamics simulation method.The physical property diagrams were plotted and compared with those of pure CO₂.The results reveal that all seven impurities can enlarge the gas?liquid coexisting region in CO₂ phase diagrams,but the enlargement extent differs. The impurities mainly expand the gas?liquid coexisting region by changing the bubble point line,while the dew point line has little change.It is found by molecular dynamics simulation that the electrostatic potential energy plays a dominant role in the CO₂ mixture containing C₂H₆,C₃H₈,and C₂H₄.Therefore,compared with the results of the mixture containing H₂,CO,CH₄,and carbonyl sulfur (OCS),its macroscopic physical properties are less affected by temperature and pressure fluctuations.

Subsea well mouth system is an essential equipment for deep⁃sea oil and gas drilling and production. Conventional casing hanger and sealing assembly running tools cannot meet the actual needs. The mechanical model of running tool for casing hanger and sealing assembly was established, which can directly describe the force on the running tool. According to the mechanical model and analysis results, the structure of running tool could be well designed. The contact and strength analysis on casing hanger carrying and driving unit of running tool were conducted using ANSYS finite element analysis software. The analysis results show that the maximum stress values of key components, such as locking block, retaining ring and mandrel of casing hanger, are less than the yield strength of material, which deformation is small enough to be ignored. The structure of the running tool meets the design requirements, and the material used selection also meets the operation standards. This work can provide design experience for the running tool of casing hanger and sealing assembly.

Stress sensitivity is one of the factors influencing fracture net deliverability of multistage fractured horizontal well for tight sandstone gas reservoirs. Based on seepage characteristic of tight sandstone gas reservoir, seepage law after fracturing work and steady seepage theory, flowing resistance method was used to derive fracture net deliverability correlation considering stress sensitivity of multistage fractured horizontal well for tight sandstone gas reservoirs, and then the correlation was used to analyze fracture parameters and stress sensitivity level on gas production rate. The results indicate that with increasing fracture flow conductivity and fracture net permeability, gas production is gradually increased, but the increase is slowed down. The unimpeded flow increases gradually with the increase of fracture half length, and increases rapidly with the increase of fracture conductivity. Therefore, in order to improve gas reservoir productivity, it is more significant to improve fracture halflength than fracture flow conductivity. The greater the stress sensitivity coefficient is, the greater the permeability decreases with the production, and the more the productivity of the gas well decreases.

The BP neura1 network and the tested gel points of the blend crude oil were studied. A prediction model based on the BP neura1 network was established to calculate the gel point of the blend crude oil. The back-propagation artificial neural network has the satisfactory nonlinear prediction ability. The gel points of the component crude oil and their proportions were taken as the input vector and the gel points of the blend crude oil as the output one. The relationship between the gel points of the blend crude oil and the component crude oil was researched. The results show that the gel point prediction model based on the BP neura1 network is better than other gel point prediction models. The maximum average deviation of the predicted gel point is only 0.128 °C and the average absolute deviation is 0.022 °C. 