Failure and mitigation study of packer in the deepwater HTHP gas well considering the temperature-pressure effect during well completion test

Abstract

During the well completion test of deepwater high temperature and high pressure (HTHP) gas well, the force on the packer changes dramatically, leading to the packer failure and serious consequences. Take consideration of the temperature-pressure effect, the packer force calculation model and the failure judgement flow diagram of packer are established based on the theory of tubing mechanics, the law of momentum conservation, and the liquid PVT properties to evaluate the reliability of packer. Dimensionless formulations to obtain the axial force and the pressure difference are proposed, and ten influencing and controllable factors are chosen to the sensitivity analysis. The results show that seven factors have great influence on the axial force and the pressure difference. Finally, two mitigation methods, installing slip joint on the tubing string and injecting nitrogen gas in the annulus, are studied for axial force and pressure difference, and the concept and calculation method of axial force safety factor are put forward. The mitigation effect of these two methods are all obvious. This study can provide theoretical guidance for packer protection during well completion test of deepwater HTHP gas well, thus can contribute to the development of natural gas and even the mitigation of greenhouse effect.