The complex formation pressure system and diverse formation fluid components during deepwater and deep drilling make it easy for gas intrusion accidents to occur. The dissolution and suspension of the intruded gas in the drilling fluid and the difference between the gas–liquid phase distribution characteristics and the gas–water two-phase flow characteristics in the wellbore lead to errors in the calculation of wellbore pressure and overflow assessment after gas intrusion. In this article, a wellbore multiphase flow model, considering gas dissolution and suspension is established, and the influence of gas dissolution and suspension in the drilling fluid on multiphase flow in the wellbore during overflow, well shutdown, and compression is analyzed with the model calculation results. The higher the drilling fluid density and yield stress are, the higher is the gas limit suspension concentration, when free gas is present in the wellbore. After the gas intrusion shutdown, when there are suspended and transported gases in the wellbore, the rate of pressure increase in the wellbore decreases after the shutdown, and the volume fraction of free gas decreases when the shutdown time is longer, and eventually all the gases will be suspended in the drilling fluid. During the pressure process, gas dissolution leads to an increase in the peak pressure in the wellbore and a delay in its occurrence; gas suspension leads to a decrease in the peak pressure in the wellbore and a delay in its occurrence. This article establishes a multiphase flow calculation model for the wellbore, considering both gas dissolution and suspension, which is a guideline for the calculation of wellbore pressure after gas intrusion.
Digital oilfield is the main means to increase production and income. Developing ultra-short radius sidetracking horizontal wells in old wells requires high-performance well trajectory control. In this paper, the ultra-short radius flexible drill pipe is designed by bionics principle, and logging tool is designed to monitor borehole trajectory in real time by using gamma ray technology. The combination of the flexible drill pipe and logging tool can realize the remaining oil recovery between dense well patterns. The dense well network determines that the drill pipe has a certain bending angle during drilling, and the remaining oil reservoir can be drilled in the shortest distance. The design of drilling tools for ultra-short radius horizontal wells for 7 “and 9-5/8” old well casings is the basis of this paper, the key is to verify the rationality of the design through experiments. The test research shows that, the strength of flexible drill pipe meets the design requirements and importing the monitoring data of gamma logging tool simulating the drilling process of the experimental well into LANDMARK software to describe the well trajectory, the radius of curvature of the deflecting section is 1.5m-2m, meeting the design expectation.
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