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Displacement flows of foamed cement in primary cementing of oil and gas wells Rahimzadeh Hanachi, Nikoo


The idea of using foamed cement, which is essentially a bubbly liquid cement slurry, in the procedure of primary cementing of oil and gas wells is to have control over the density and be able to have lighter cements. However, some complications arise from the liquid-gas (compressible) mixture. First, there is an ongoing concern about the stability of the foamed slurry, e.g. as was queried in the enquiry into the 2010 BP Macondo incident. Secondly, there are questions regarding how the rheology of the foamed slurry should be modelled. Thirdly, there are questions regarding the stability of the placement flow itself, i.e. assuming that the foamed slurry itself remains intact. Here we have developed two preliminary models of primary cementing that include foamed cements. A one-dimensional hydraulic flow model is derived for displacement of foam flow inside the casing and annulus. In the annular region outside the casing, we modify the model developed to model laminar displacement flows of incompressible fluid, via a two-dimensional gap-averaged model. The main differences of our model compared to an incompressible fluid displacement are: (i) flow in our case is represented with a mass-flux stream function. (ii) density and rheological properties of foam are pressure dependent. Numerical simulation of displacement flows using the resulting model show that the annular flow exhibits buoyancy driven instabilities in many situations as the foam advances up the annulus.

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