To elucidate the mechanism by which pipeline shear increases the gel point of crude oil treated with a polymeric pour point depressant (PPD), pipeline⁃shear simulation experiments were conducted on T crude oil based on energy dissipation theory. Microscopic observations combined with ImageJ image analysis were used to characterize wax crystal morphology before and after shearing. The results showed that, after the addition of 25 mg/kg of PPD and heat treatment at 50 ℃, the gel point of T crude oil decreased from -8 ℃ to -14 ℃. Following simulated pipeline transportation, the gel point of the treated crude oil increased to -5 °C, representing greater deterioration than that observed for untreated crude oil. Each high⁃speed shearing event increased the gel point of the treated oil by 3-4 ℃. Microscopic analysis showed that the PPD promoted wax crystal aggregation and growth through co⁃crystallization and adsorption, reducing the crystal count from 605 to 272 and increasing the mean crystal area from 5.58 μm² to 7.33 μm². However, shear disrupted the aggregated wax crystal structures, causing the crystals to redisperse; wax crystal number increased to 771, while average wax crystal area decreased to 1.36 μm². This increased the dispersion and surface energy of the system, leading to a higher gel point. These findings clarify the microstructural mechanism by which shear weakens the effectiveness of polymeric PPD treatment and provide a theoretical basis for assessing shear⁃related safety during the pipeline transportation of waxy crude oil.

The minimum miscible pressure is one of the important parameters of CO2 injection in oil field. In order to determine the minimum miscible pressure between crude oil and CO2 in the tight reservoir of lucaogou formation, jimusar sag, Xinjiang, the laboratory slim tube test and interfacial tension test were carried out. The results show that the MMP measured by slim tube test in Xinjiang tight oil reservoir is 18.70 MPa, slightly higher than the MMP measured by the interfacial tension experiment, which is 18.44 MPa. The difference between the two is 1.4%, and both lower than the reservoir pressure of 43.00 MPa. Therefore, CO2 and crude oil can be miscible under the reservoir conditions. When the equilibrium pressure increases, the IFT decreased more as more CO2 dissolved in crude oil. When the system equilibrium pressure increased from 0.73 MPa to 28.46 MPa, the IFT value between crude oil and CO2 decreased from 22.62 mJ/m2 to 1.83 mJ/m2. When the equilibrium pressure was between 0.73 MPa to 13.33 MPa, the dissolution of CO2 in crude oil took the leading role. However, when the equilibrium pressure was between 15.84 MPa to 28.46 MPa, the extraction of light components in crude oil took the leading role, and the interaction mechanism between crude oil and CO2 changes from CO2 solubility to CO2 extraction of light components at the pressure of 13.67 MPa. Through the experimental study, the understanding of the MMP of the target reservoir and the microscopic interaction mechanism between crude oil and CO2 is deepened, which provided theoretical support for the formulation of CO2 injection development of the target reservoir.

In order to research on the impact of imbibition effects, mechanisms and the correlation factors of the tight oil cores, the experimental devices of tight core imbibiton were established. The experiments of oil-water imbibition of tight sandstone were carried out. The effects of temperature, pressure and surfactant on the oil-water imbibition in compacted core were studied. The curves of imbibition efficiency versus time, characteristic points of curve and the influential factor of imbibition were analyzed. The imbibition law and characteristics of tight sandstone core were obtained. The results showed that the effect of imbibition was mainly occurred on the surface layer of the tight oil core. The temperature had a large effect on the second stage of imbibition. The oilwater imbibiton efficiency of the single tight oil core is about 10%, which is about 25% under the formation conditions.

      There is usually a starting pressure gradient in the tight oil. This article considers the seepage law of the crude oil flowing from the matrix to the fractures in the formation under the premise of starting the pressure gradient and some assumptions. Through the establishment of numerical model, the relationship between the pressure, permeability, core size and other factors and the degree of failure recovery in the onedimensional space is analyzed, as well as the threedimensional plate is drawn. The results show that when the core scale is very small, the main factors affecting the degree of recovery are the failure pressure difference. At the same time when the scale increases, the relationship between the recovery degree and the core length and permeability is more and more significant. Then, based on the conclusion of the previous the paper put forward the empirical formula considering the degree of calculation and recovery under various factors, and extend the space to three dimensions. On the basis of one dimensional revise the formula, the empirical formula of the failure rate of three dimensional matrix failure is obtained. It provides some reference for production practice.