Expansion additives have been used in cement plugs to mitigate the potential risk of plug failure resulting from shrinkage. These additives are effective only when their amount is tailored for downhole boundary conditions, and their role should be well understood. This work discusses using an improved testing method that enhances the dependability of the volume change measurement and exhibits the impact of test boundary conditions on the shrinking and expanding behaviors of cement plugs. Boundary conditions investigated with this method include temperature, pressure, water access to the cement from the formation, and the role of mechanical constraints. Dependability is demonstrated by verifying the repeatability and reproducibility of the method at two different laboratories. Together with the noninvasive continuous volume change, supplementary measurements, such as ultrasonic compressive strength, tensile strength, and chemical composition analysis, have provided inferences about the mechanism of volume change. The new method embodies all attributes listed in API 10 TR2 (1997), including a constant external stress state in all measurements and a constant pore pressure during total volume change measurement. The results of percentage volume change from this test method present an extremely small variance, highlighting its repeatability; additionally, the measurement was reproducible between laboratories. Expansion value increased with a decrease in confining pressure, and excessive expansion in the absence of an effective confining pressure produced weak samples. The absence of outside water caused cement containing the expansion aid to shrink more than its neat equivalent; such observations highlight the importance of fluid boundary on the action of expansion additives. These observations were possible because the test method can capture temporal and boundary condition effects more aptly. Thus, the improved method provides a dependable measurement for tailoring plug properties.

Cementing a casing string across weak formations or depleted reservoirs has the added challenge of tailoring the cement slurry to meet delivery criteria (i.e., density and rheology) while maintaining the mechanical properties of the set cement necessary to provide a dependable barrier. To help prevent fracturing the formation and inducing losses, cement density is often reduced, which strongly influences the mechanical properties of set cement. Common strategies for reducing cement density consist of adding water in the cement slurry; using additives such as hollow glass microspheres (HGS), synthetic latex, and elastomers; using foam cement; or adding resin. This paper discusses how cement slurries with reduced densities are designed using both traditional and alternative methods of making cement/resin composites and provides insight into the advantages and drawbacks of each. Stable cement slurries with a density of 13 lbm/gal were designed, and placement characteristics of thickening time and rheology were evaluated for the liquid cement slurry. Unconfined compressive strength (CS), Young's modulus (YM), tensile strength, permeability, and shear bond were investigated on the cured samples. Before taking mechanical and permeability measurements, slurry stability was verified using sedimentation testing. Any slurry that did not exhibit the necessary stability was redesigned and tested again. Only the final slurry designs exhibiting stability are discussed in this paper. Cement-resin composite cements exhibited similar performance to those containing HGS in terms of CS, YM, tensile strength, and shear bond but exhibited greater than two times the CS when compared to the synthetic latex modified, water-extended, and elastomeric slurry designs. The cement-resin composite provided almost twice the shear bond strength and increased tensile strength by 50% compared to other slurry compositions. In the current work, cement-resin composite, synthetic latex modified, microbead-based, water-extended, and elastomer-modified slurries are compared at 13 lbm/gal. Various parameters, such as mixability, ease of placement in the annulus, strength development, and long-term cement integrity, are evaluated. Traditional and newly introduced techniques for reducing cement slurry density and the resultant mechanical properties of the set solids are investigated. This information provides an alternate method of using cement-resin composites for designing and delivering dependable barriers tailored for low density applications.

Fluid systems used for servicing wellbores are usually a combination of particulate materials of varying specific gravity, particle size, aspect ratio, and reactivity, such as lightweight materials/weighting agents, clays, fibers, elastomers, polymers, resins, salts, and cementitious materials in water or oil media. These fluids are more commonly referred to as -complex fluids‖ and often exhibit a high degree of non-Newtonian and time-dependent behavior. To more efficiently and expeditiously perform well operations, it is beneficial to accurately probe the rheology of fluids (and their admixtures) under downhole conditions.A novel, helical-shaped stator-rotor assembly was designed and developed to work around measurement errors arising from sample inhomogeneity, particle separation, wall slip, and coring-related issues with commonly used geometries, such as those of a bob/sleeve and vane. The rotor blade arrangement is a double helix with cut flights, whereas the stator unit has blades that are manufactured by parting a coaxial double helix offset to the envelope of the rotor. Constant relative separation between the stator blades and rotor vanes is maintained in all planes to create shear geometries that enhance in-situ mixing. This was leveraged to conducting compatibility testing.Torque and rev/min data was collected for eight different Newtonian fluids with viscosities ranging from 10 to 1000 cp. The power number and impeller Reynolds number were plotted to derive functional relationships between these quantities in the laminar and turbulent regimes. Various complex fluids, including fracturing gels, viscoelastic fluids, oil, water-based muds, spacers, and cement slurries were tested on the helical mixer, a triangular impeller, and Couette geometries for comparative mathematical modeling.A unified algorithm and data analysis protocol featuring the four-parameter generalized Herschel Bulkley model is presented to derive rheograms and yield stress. A comparison of experimental results with computational fluid dynamics (CFD) simulations is also presented.

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.