Abstract

There is a growing need for comprehensive multi-phase hydraulic models that can accurately model more complex well control situations associated with the use of Managed Pressure Drilling (MPD) techniques, complex well geometries, High-Pressure High-Temperature (HPHT) conditions, riser gas unloading, etc.

A new thermal model integrated with previously developed multi-phase hydraulics software is presented here to address this need. This de-coupled thermal model is added to a sophisticated multi-phase flow code to estimate the mud temperature in the drillstring and the annulus and in the formation adjacent to the well during complex well control situations. The model uses an explicit finite volume approach and solves the mixture energy equation for the wellbore fluids, assuming that all the phases are at thermal equilibrium. Heat transfer between the drillstring and the wellbore fluid, and between wellbore and formation is calculated using a thermal resistance network. Axial heat conduction in the mud and heat generation (e.g. at the bit) are accounted for. The steady-state results of the proposed thermal model are compared to the steady-state Hasan and Kabir model and commercial software. In addition, the transient, time-dependent temperature behavior during mud circulation is compared against the results of the commercial software. Results show a very good match for both steady-state and transient cases.

Kick scenarios are simulated to show the importance of accurate temperature estimation of the drillstring and annulus fluids in HPHT conditions. Using advanced numerical schemes, a comprehensive model for heat transfer and energy storage in combination with a user-friendly Graphical User Interface (GUI) makes this model a robust tool for estimating the transient temperature profile of the mud and the formation. The model allows for evaluation of crucial parameters during well control, such as the wellbore pressure and temperature profiles, increased outflow and pit gain during kicks, gas thermodynamic behavior including solubility and unloading at low pressure conditions, gas rising velocity, and even temperature-dependent formation strength. These added features provided by the model come without loss of previous modeling capabilities, such as accounting for area discontinuity in the well and drillstring, gas dissolution in mud, non-Newtonian fluid rheology, MPD techniques, and arbitrary 3-D well trajectories.

Details of the new model and the simulation approach are shared, and various applications of the new thermal modeling capability are illustrated.

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