Effect of fluid rheology of hole cleaning in highly-deviated wells
Vinod, Palathinkara S.
McIntire, Larry V.
Doctor of Philosophy
One of the technical challenges in deviated drilling is the transport of drill bit cuttings to the surface. The complexity arises due to the narrow settling clearance for the cuttings and the presence of a cuttings bed on the low side of the bore hole. Fluid rheology is the determining factor in the efficiency of this operation. Drilling fluid selection for possible field use is the focus of this dissertation. The problem has been treated with a two-pronged strategy: (i) macroscopic studies that involve numerical models for the prediction of effects of rheology on drilling fluid flow through deviated bore holes; and (ii) microscopic experimental studies that provide physical insights into the fluid forces and relevant rheological parameters in cuttings resuspension. The objective of this study is to propose guidelines for fluid selection and rheological characterization of drilling fluids for the industry. The numerical study demonstrates that power law index is a significant parameter in determining the local flow regime in the different regions of the annulus and hence accurate control of power law index is critical in optimizing bore hole flow. In laminar flow, the shear thinning nature of a fluid does not aid flow through the narrow regions. Turbulence in the wider regions of the annuli aids flow through the narrow regions. The wall shear stresses are dependent only on the pressure drop, gap width and the local flow regimes. Eccentricity is found to hinder flow through the narrow regions of the annuli and certain combinations of rheology and eccentricity can cause stationary 'plug like' zones inside the annuli. The experimental study combined with microscopic calculations identified lift force as the limiting force in particle mobilization and put in perspective the possible importance of normal stresses due to the viscoelastic behavior of the fluid. It is shown that viscous characterization of the fluid is inadequate to predict the particle mobilization velocities even for very simple situations. Characterization of the fluid viscoelastic properties can provide qualitative information on the importance of fluid rheology for particle mobilization. The parameters of interest identified are the magnitude and strain sensitivity of linear viscoelastic moduli.
Petroleum engineering; Chemical engineering; Mechanical engineering