Complex structure wells are now widely used in the development of marine oilfield, old oilfield and low
permeable oilfield. During drilling operations, if the fluid velocity is lower than a critical value in annulus, cuttings in the
highly-deviated segments and horizontal segments will accumulate and eventually develop cuttings bed, which affects the
rate of penetration (ROP) and downhole safety. As a result, numerous inventions which show different hole-cleaning
detection methods can be applied to determine cuttings concentration or hole-cleaning efficiency, and there are three
methods for good hole-cleaning condition. The fluid rate control methods include increasing flow rate and injecting slug.
The chemical methods include changing the rheology of drilling fluid and adding fiber sweep into drilling fluid. The
mechanical methods include using pipe joint, annulus reducer, and different types of blades tool for rotary drilling, and
centralizer and fluid velocity shift device for non-rotary drilling and rotary drilling. This review presents a summary of the
main United States and Chinese patents available on hole-cleaning techniques.
Keywords: Chemical method, complex structure well, flow rate control method, hole cleaning, mechanical method.
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