Wellbore Temperature and Pressure Field in Deep-water Drilling and the Applications in Prediction of Hydrate Formation Region

Abstract

In the process of deep-water drilling, gas hydrate is easily formed in wellbores due to the low temperature and high pressure environment. In this study, a new, systematic, and accurate prediction method of temperature, pressure, and hydrate formation region in wellbores is developed. The mathematical models of wellbore pressure and transient heat transfer are established, the numerical solution method based on fully implicit finite difference method is developed, and the accuracy is verified by comparing with the field measured data. Combined with the hydrate phase equilibrium model, the hydrate formation region in wellbore is predicted, and the sensitivity effects of nine factors on wellbore temperature, pressure, and hydrate formation region are analyzed. Finally, the influence regularities and degree of each parameter are obtained. The increases of circulation time, geothermal gradient, displacement of drilling fluid, and injection temperature will inhibit the formation of hydrate in wellbores, and the influence degree increases in turn; the increases of wellhead backpressure and seawater depth will promote the formation of hydrate in wellbores, and the influence degree increases in turn. The changes of drilling fluid density, well depth, and hole deviation angle have little effect on the formation of hydrate in wellbores.

Solution and Analysis of Wellbore Temperature and Pressure Field Coupling Model under Lost Circulation

“…Although the research on wellbore heat transfer of drilling fluid under no-loss circulation conditions has become mature, there are few studies on variable mass heat transfer of annulus fluid under loss circulation. − In 2017, Chen et al established the first variable mass heat transfer model in the wellbore under the lost circulation condition and also proposed a method to judge the position of the loss zone according to the temperature gradient curve. However, due to its failure to fully consider the heat source generated in the drilling process and the influence of the casing program on the wellbore temperature distribution, the model has a large error in the drilling process of deep and ultradeep wells.…”