Summary
This study aims to investigate the hole-cleaning process during the flow of
a drilling fluid consisting of a gas and a liquid phase through a horizontal
annulus. Experiments have been conducted using the Middle East Technical
University (METU) multiphase flow loop under a wide range of air- and
water-flow rates while introducing cuttings into the annulus for different
amounts. Data have been collected for steady-state conditions (i.e., liquid,
gas, and cuttings injection rates are stabilized). Collected data include flow
rates of liquid and gas phases, frictional pressure drop inside the test
section, local pressures at different locations in the flow loop, and
high-speed digital images for identification of solid, liquid, and gas
distribution inside the wellbore. Digital image-processing techniques are
applied on the recorded images for volumetric phase distribution inside the
test section, which are in dynamic condition. The effects of liquid and gas
phases are investigated on cuttings-transport behavior under different flow
conditions. Observations showed that the major contribution for carrying the
cuttings along the wellbore is the liquid phase. However, as the gas-flow rate
is increased, the flow area left for the liquid phase dramatically decreases,
which leads to an increase in the local velocity of the liquid phase causing
the cuttings to be dragged and moved, or a significant erosion on the cuttings
bed. Therefore, increase in the flow rate of gas phase causes an improvement in
the cuttings transport although the liquid-phase flow rate is kept constant. On
the basis of the experimental observations, a mechanistic model that estimates
the total cuttings concentration and frictional pressure loss inside the
wellbore is introduced for gasified fluids flowing through a horizontal
annulus. The model estimations are in good agreement with the measurements
obtained from the experiments. By using the model, minimum liquid- and gas-flow
rates can be identified for having an acceptable cuttings concentration inside
the wellbore as well as a preferably low frictional pressure drop. Thus, the
information obtained from this study is applicable to any underbalanced
drilling operation conducted with gas/liquid mixtures, for optimization of flow
rates for liquid and gas phases to transport the cuttings in the horizontal
sections in an effective way with a reasonably low frictional pressure
loss.
© 2012. Society of Petroleum Engineers
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History
- Original manuscript received:
15 January 2011
- Meeting paper published:
23 April 2010
- Revised manuscript received:
8 September 2011
- Manuscript approved:
13 September 2011
- Published online:
12 July 2012
- Version of record:
12 September 2012
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