Cuttings transport: On the effect of drill pipe rotation and lateral motion on the cuttings bed

Alexander Busch, Stein Tore Johansen
2020 Journal of Petroleum Science and Engineering  
A B S T R A C T Drill pipe rotation is considered a relevant factor for cuttings transport and hole cleaning. However, in the term "rotation" is often used as a moniker for the combination of plain drill pipe rotation around its own axis and more complex lateral motion, as many laboratory setups feature an unconstrained drill string. Lateral motion is generally considered to benefit the transports of cuttings due to increased bed agitation. By means of Computational Fluid Dynamics, we have
more » ... tigated the effect of synchronous and asynchronous whirling drill string motion on the cuttings bed and cuttings transport for water and a more viscous, shear-thinning fluid using the Two Fluid Model in conjunction with the Kinetic Theory Of Granular Flows and closures from soil mechanics to rheologically describe granular matter. The dynamic mesh capability of ANSYS Fluent R17.2 is exploited to account for the orbital motion of the drill string. In addition, three base cases (negative eccentric, concentric, and positive eccentric) are investigated for comparison. Whirling motion helps tremendously to disperse the solids into the main flow region and hence improves the quality of cuttings transport and hole cleaning, with synchronous whirl by far outperforming asynchronous whirl due to the cumulative tangential and radial velocities. The effect is much more prominent for water than for the more viscous, shear-thinning fluid because the latter already shows a comparatively good cuttings transport performance. Moreover, in case of the more viscous, shear-thinning fluid, the positive eccentric annulus provides an even better cuttings transport capability, if comparison is made on equivalent pressure gradients. Because of the higher viscosity level, the whirling motion reduces the axial throughput, which despite the increased bed agitation results in worse performance compared to the positive eccentric case. .no (A. Busch). 1 Strictly speaking, one needs to distinguish between individual drill pipe elements and the drill string made up of several drill pipe elements. However, for simplicity and because we here focus on an annular element with length L < 10 m, we use the terms interchangeably. 2 The coordinate system employed in this study is depicted in Fig. 1 and defined as follows: Assuming a horizontal wellbore, i.e. an inclination of 90 � as used in the petroleum industry, the streamwise direction is positive x, the vertical direction against gravity is positive y, and the direction out of the plane is positive z. Thus, negative eccentricity is characterizing a drill pipe out-of-center towards the lower side of the annulus, whereas positive eccentricity is the opposite.
doi:10.1016/j.petrol.2020.107136 fatcat:dvp2pe3iq5c7vf2bk5xpdotjgu