Review of Hole Cleaning in Complex Structural Wells

Complex structural wells are widely used in the development of marine oilfield, old oilfield and low permeable oilfield. However, poor hole cleaning is often occurred in the highly-deviated sections and horizontal sections of the complex structural wells, which affects rate of penetration and downhole safety. The methods to study cuttings transport can be normally divided into four types: 1) experimental observations, 2) CFD simulations, 3) theoretical correlations and models and 4) field tests. Experimental observations and CFD simulations are mainly used to analyze the effects of different parameters on hole cleaning and obtain some valuable data. Theoretical models and correlations are mainly applied to calculate cuttings bed height, critical velocity and etc to provide the guidance for the design of hydraulic parameters. The accuracy of the first three types are checked by field tests. In this paper, the effects of flow rate, inclination, mud rheology, drillpipe rotation and other factors on hole cleaning, and some typical correlations and models were briefly reviewed before 2000 years, and some new research findings were detailedly addressed. In addition, CFD simulations also were introduced. Although major improvements have been achieved in the past several decades, building a comprehensive and proven model requires much more experimental researches, CFD simulations, in-depth theoretic studies and field tests due to the complexity of cuttings transport under multi-factor interactions.