Multicomponent thermal fluid flooding has become a widely used and very effective heavy-oil recovery technology, but the harsh CO 2 -O 2 -Cl − environment can lead to serious corrosion perforation failure of the pipeline. Therefore, the influence of O 2 content and main controlling factors on corrosion perforation were investigated through a weight-loss experiment, corrosion defect test, characterization and grey correlation method. The results showed that, with the increase in O 2 content, the general corrosion rate and localized corrosion rate increased. The uneven protection performance of the product after the addition of O 2 was found to be the key cause of localized corrosion. In addition, the synergistic effect of O 2 -Cl − promoted the lateral and longitudinal expansion of pits. The results of the grey correlation showed that the temperature (30-120 °C) had a greater impact on localized corrosion compared with the content of O 2 (0-0.045 MPa) and Cl − (0-16,000 mg/L).

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The oilfield is unable to carry out normal temperature gathering and transportation (NTGT) process, since the feasibility has not been verified and the minimum flowable temperature (MFT) calculations have not been proposed. In this paper, the simulation of parameters such as temperature and pressure of the pipeline network are performed based on the production data of the oilfield during the period of unheated gathering. It is verified that the temperature and pressure errors of the simulation results are less than 0.79 °C and 0.1 MPa, respectively. It is found that the gathering network of this oilfield can operate normally in winter, which proves the feasibility of NTGT theoretically. Through calculating the flow parameters of the gathering network under extreme cold conditions in winter, a novel formula for calculating the MFT of oil-gas-water three-phase mixed transmission process is proposed, where the shearing effect of gas on fluid has been extra considered. The fitting effect of MFT formula on a single well is better than that on multiple wells. The application of the fitted MFT formula in situ as well as the corresponding preliminary oilfield tests has proved the feasibility of the NTGT process. Thus, the oilfield gathering network is successfully guided to change from a heated gathering process to a NTGT process.

For long-distance natural gas pipes crossing highway, the changing load of vehicles is the most important and frequently acting-live load on buried pipes, which poses a serious threat to the integrity of the pipe. This study has designed and built a buried pipe stress test experimental system. The experimental system is mainly composed of a sealed pipe, an air compressor, and a stress-strain testing system. In this study, a total of 24 sets of stress test experiments are carried out. The research conclusions are as follows. The maximum stress of the pipe occurs at the 12 o’clock position of the pipe when the vehicle load is rolled at the middle. The increase in vehicle load results in an increasing pipe stress value. Both of the vehicle speed and the internal pressure play a certain role in protecting the pipe. After carrying out a real experimental case via Sinopec’s natural gas pipe crossing the highway, we have found that it can withstand the rolling load of a heavy vehicle of 78t, when the L325 steel pipe section that crossing the Grade-4 highway has a buried depth of 0.8m, a diameter of 355.6 × 5.6mm, and a internal pressure of 1.03MPa.