Hole cleaning and drilling fluid sweeps in horizontal and deviated wells: Comprehensive review

Abstract

Horizontal wells provide high drainage area within the reservoirs. Advancements in horizontal drilling technologies are utilized to develop unconventional resources such as shale gas and coal bed methane. However, wellbore instability and difficulties in hole cleaning are combined with high-temperature high-pressure conditions in such sensitive formations. Inefficient cuttings removal out of the wellbore results in increasing drag and torque, pipe stuck and may induce lost circulation and consequently increases drilling non-productive time (NPT). Various drilling methods and hole cleaning technologies including downhole tools and complex fluid systems have been implemented to transport cuttings out of horizontal and highly deviated wellbore sections. This review explores the factors that lead to cuttings settling and resuspension in horizontal and deviated sections. Furthermore, it discusses various types of drilling sweeps and additives used with water, oil and gas based drilling fluids to improve the cuttings lifting efficiency in horizontal wells. Bio-based additives and nanomaterials used with unconventional reservoirs are also highlighted. Moreover, different methods used in drill cuttings removal are illustrated. Factors affecting the cuttings removal have also been evaluated and general guidelines for selecting additives and sweep fluids are established. Finally, the main laboratory techniques used to analyse cuttings settling behavior and fluid stability are presented.