PRESSURE DROP AND CUTTINGS CONCENTRATION ESTIMATION IN HORIZONTAL SECTION OF WELLBORE DURING UBD OPERATION USING ANSYS-CFX CFD

Pressure drop and cuttings concentration are considered as sensitive issues in underbalanced drilling, especially when dealing with three phase (cuttings-gas-liquid)flow in horizontal, deep and extended reached wells. Improper estimation of the two mentioned may lead to drilling complications such as reduction in rate of penetration, pipe sticking, increase in torque and drag force and cutting bed development. In order to address this issue, there is a need of understanding the fundamental behavior of the three phase flow in the annulus and identify the most influencing parameters. In this project, effect of rate of penetration (ROP) and fluid velocity at the annulus is analyzed by simulating the three phase flow in a horizontal section of the wellbore by using a commercial package of computational fluid dynamic (CFD) software known as ANSYS CFX 14. The length of the horizontal section is 2ft of diameter 2.91inch and the inner eccentric drillpipe diameter is 1.85inch.
The simulations were conducted at steady state flow and as a result flow patterns were identified as well as volumetric concentration of cuttings and pressure drop were inferred.
Initially, cutting bed was observed at the entry section of the annulus due to rate of penetration and low annular velocity. But as the annular velocity increases due to increase in gas superficial velocity, the bed decreases and pressure drop decreases as well. After that when cutting bed disappeared completely, the pressure drop increase again due to increase in the mixture fluid density.
However, as the ROP increases, the cuttings concentration increases, but not much change is observed in the trend of pressure drop due to the presence of the gas causing turbulence at the annulus.
The result generated by the simulation is verified with the experimental data taken from Ettehadi Osgouei et al (2010) paper and it shows a good agreement with an error difference of less than 20%. So this implies that drilling Engineers can apply
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ANSYS-CFX14 to estimate pressure drop and cuttings concentration for underbalanced drilling program.