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Fluid and Temperature structure interaction

The fluids filling a well have two important effects. First, they affect any drillstring/BHA motions because of the friction they exert. In this respect the resonance frequencies depend on the viscous effects of the fluids and the oscillation amplitudes are damped by them.

Second, the fluids exert pressure on the structural elements of the well, which is important for the casing design. This pressure not only depends on the fluid properties i.e. the equation of state (often called PVTs) but also depends on the fluid flow rate and temperature vertical profile (fluid and temperature). A fluid circulating inside a well carries thermal energy. The local temperature and therefore pressure then result from the complex energy transfer phenomena (convection, conduction) within the well and with the surrounding formation.

Our goal is to develop an accurate numerical tool handling the evolution of pressure and temperature inside a well and along the different phases of its life : drilling, cementing, producing.

Permanent & transient flow

3D detailled CFD calculation of mud flow around rotating pipe

3D detailled CFD calculation of mud flow around rotating pipe

We are currently developing a calculation code for multiphase fluid motions inside the different parts of a well : pipes, annuli. This code handles several predefined equations of state for water muds, oil muds and cements. In the permanent flow regimes it calculates the pressure at any depth and for any flowrate in the central pipe and the surrounding annuli. Pressure friction losses are taken into account for the different rheological law that may occur (Newtonian fluid, power-law fluid, Herschel-Bulkley fluids) and the laminar or turbulent flow regimes. The fluid dynamics is considered in 1D along the well axis, yet in the cases where the turbulence effects cannot be neglected it relies on 3D computational fluid dynamics (cf figure).

Work is under progress on the one hand to address the transient flowrates and on the other hand to enable the code to perfom on production fluids.

Thermal transfer

Fluid properties like pressure change with temperature, thus thermal energy transfers are crucial to estimate the structure / fluid interaction. The fluid dynamics effects we described in the previous section need to be completed by the thermal tranfers resulting from conduction, forced convection and free convection. Our purpose is to introduce these processes in a 2D framework (well axis and radial directions). In a first step we have developped a 2D code for thermal transfer through conduction. This is mostly meant to address heat fluxes inside a geological formation. We are now in the process of accounting for forced thermal energy convection by the fluid and we will then address free convection processes.