s State-of-the-Art Hole-Cleaning Techniques in Complex Structure Wells

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.