Placing the cement slurry in the entire annulus, in both the wide and narrow sides, is essential to achieving effective zonal isolation. Well conditions, such as deviated wellbore geometry, eccentric annulus, and gelled drilling fluid, pose unique challenge in achieving this objective. It is known in the industry that pipe movement helps improve hole cleaning and cement-slurry placement. However, the quantitative effect of pipe rotation on hole cleaning and cement-slurry placement for a given eccentricity, flow rate, and geometry was not well studied. Hence, it was difficult to design a primary cement job where the effects of all these parameters were considered at the same time and optimized for best results. The effective velocity and pressure drop in an eccentric annulus with and without pipe rotation is modeled for Herschel-Bulkley fluid. This is then extended to evaluate the effect of pipe rotation on hole cleaning and cement-slurry placement. The modeling clearly demonstrates the improvement in hole cleaning from pipe rotation in an eccentric annulus. Now there is a tool available to study the interaction of various factors on hole cleaning and optimize them for the well in question. The results from the modeling study have been compared with field data. The comparisons show a good match between the improvement in cement-slurry placement predicted that was inferred from the cement bond logs. The study clearly indicated the importance of using representative rheological model and input values. The modeling results and field validation are presented and discussed. The work presented in this paper should help the industry optimize the various factors during a cement job to help maximize hole cleaning and cement-slurry placement in the wide and narrow sections of the annulus. This should help in achieving zonal isolation for the life of the well and reduce operating expenses by reducing remedial jobs. Introduction In recent years, the study of the hydraulics effects of drillpipe rotation on annular pressure drop and equivalent circulating density (ECD) has been receiving a great deal of attention. Initially, researchers focused on theoretical studies and laboratory measurements of pressure drop (?P) (Luo and Peden 1987; Walker and Al-Rawi 1970). In these studies, the authors observed that, under laminar-flow conditions, drillstring rotation served to lower pressure drop and ECD. Several studies were later conducted in support of slimhole drilling efforts where the Di/Do ratios are quite high (0.75 to 0.85). In one of the slimhole drilling studies (Bode et al. 1991), data showed increased ?P with increasing drillpipe rotation speed (up to 200 rev/min) for fluids with Reynolds numbers < 2000. In the second slimhole study (Delwiche et al. 1992), field measurements of drillpipe-rotation effects on pressure drop were made, and the results showed increasing pressure drop with drillpipe rotation speed. In a third slimhole drilling study (McCann et al. 1995), the authors concluded ?P decreased with increasing drillpipe rotation speed for power-law fluids in laminar flow. In all of these early studies, no attempt was made to model the results into a coherent calculation scheme. In Marken et al. (1996), the authors reported increasing measurements of ?P with increasing drillpipe rotation speed (18 to 67% increase over the ?P reported at 0 rev/min). They cited the occurrence of centrifugal instabilities (Taylor vortices) and uncertainties in annular eccentricity and drillstring motion and vibration as reasons for industry models to incorrectly predict annular pressure drops with drillstring rotation. Later, others studied the effects of drillstring rotation in fluids in laminar flow from a theoretical perspective and concluded rotation had a significant effect on pressure drop, especially in smaller-diameter gaps through which fluid was moving (Ooms and Kampman-Reinhartz 2000). However, the modeling in this work was valid for Newtonian fluids only.

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Accurately measuring the rheology of fluid systems under downhole conditions is recommended for the success of well construction. The rheological fingerprints of fluids and their admixtures deployed downhole during wellbore servicing provide a basis for predicting interfacial fluid movements and associated effects on bottomhole circulating pressures. Rheology measurements can also provide a direct indication of any detrimental physical and/or chemical reactions that might occur when the fluids intermix and/or contaminate one another during and after the placement process. A need has existed for some time within the industry for high-pressure/high-temperature (HP/HT) rheology equipment capable of in-situ fluid transfer to change compositions on-the-fly, and easy to clean and maintain considering the abrasive and settable nature of cementitious fluids. This paper discusses an innovative design developed for a fully automated slurry rheometer capable of dosing contaminant fluids in and out of fluid samples to vary composition, mix homogenously in-situ, and measure compatibility between fluid systems at various volumetric compositions—all while maintaining in-situ wellbore test conditions. The rheometer cell is a four-piece design that houses a novel magnetically coupled double helical rotor with cut flights and intermeshing helical blades on the stator to allow mixing and measuring at the same time while overcoming operational issues, such as wall-slip, particle settling, sample coring, and aid in-situ homogenization. A first of its kind, noncontact, zero friction magneto-resistive torsion measurement module with selectable range capabilities and large separation offset (6 to 8 in.) from moving parts is discussed in addition to its usability on both thick pastes as well as thin fluids. A separate design of a high pressure slurry dosing unit that allows for compatibility measurements is discussed. Operating principles, design concepts, engineering development for modularity, calibration data, and slurry test results are presented.