A well-executed cement operation is fundamental for successful zonal isolation. One method used to confirm the success of a cementing operation is cement bond-log (CBL) analysis. Various factors contribute to good bond strength at the casing-cement interface; a better shear bond helpsminimize the risk of communication between different zones and also maximize production by avoiding undesirable fluid diversion during well intervention. To enhance shear-bond strength, a thin layer of coating material can be applied on the external surface of casing before running itin the well. Variouscoating techniquesare available, such as spraying, dipping, or simply brushing. Polymer emulsions, thermosetting polymers, and inorganic-based coatings can be applied. This paper studies the effect of various coating materials on shear-bond strength. A coated casing sample was concentrically placed inside another largercylinder and cured after filling the annular space with cement slurry. Once cured, the shear-bond strength was experimentally measured using a hydraulic press. The results obtained with various coating materials are compared to those from an uncoated control sample. The shear-bond setup was prepared with neat standard cement slurry and cured for 3and 7days for testing. Three different types of casing coating wereevaluated for enhancing shear-bond strength—inorganic-based, aqueous polymer emulsion, and thermosetting resin. All three coatings providedenhanced shear-bond strength compared to the control sample. The inorganic-based coating almost doubled the shear-bond strength. The aqueous polymer emulsion coating increased shear bonding by approximately 30%. Finally, the thermosetting resin coating resulted in a much smaller increase in shear bonding compared to the other treatments; however, it was observed to provide better resiliency while applying loads during testing. A thin layer of coating onthe entire length of a casing column does not significantly increase costs. On the contrary, significant value is providedthrough better shear-bond strength and potential corrosion resistance. Therefore, this practice can eliminate the necessity of remedial treatments later. Additionally, applying the inorganic-based coating on the outer surface of casing pipe provides additional bond-strength between the cement and casing, minimizing the risk of inner debonding. The coating application process is operationally simple and can be readily implemented, and it provides a low-cost, dependable barrier. In addition to providing better bonding, coating can also inhibit corrosion and increase the life of the tubular.

Well-executed cementing is a key parameter for achieving successful zonal isolation to help ensure long-term integrity of the wellbore. Casing centralization, design of wellbore fluids for maintaining density hierarchy, rheological hierarchy and compatibility, and efficient mud displacement are some important factors that affect the efficiency of the cementing operation. For achieving efficient mud removal, and for keeping the drilling mud from direct contact with cement slurry, typically spacer fluids are pumped before cement placement. This can also aid cleaning the casing and formation surface of oil film, thereby helping achieve good bonding with the set cement. Spacers are usually water-based fluids with added surfactants for cleaning the casing and formation surfaces. This surfactant pack is usually optimized using bulk conductivity measurements such that an equi-volume mixture of spacer fluid and mud forms water-external emulsion. However, this might not ensure rheological compatibility between the optimized spacer and the drilling mud at all possible volume ratios. In addition, because the conductivity is a bulk property measurement, it does not give enough information about its wetting characteristics with the casing surface for better bonding. In the present work, a spacer surfactant optimization procedure is evaluated for three different combinations of drilling mud base oil and the surfactant packs. After surfactant pack optimization, the rheological compatibility between the drilling mud and spacer fluid is measured. The rheological measurements showed that not all volume combinations of the optimized spacer and the drilling fluid are compatible. Hence, the spacer surfactant pack is re-optimized for removing these rheological incompatibilities. Further, shear-bond experiments are conducted to measure the efficacy of spacer to clean the casing surface. It is observed that the shear-bond strength varied between the combinations of drilling fluid base oil and the surfactant pack. This study helps in terms of identifying and optimizing a suitable surfactant pack for given drilling fluid base oil for achieving better compatibility and casing cleaning.

Drillpipe (DP) work strings are used for continuous operations during the drilling phase and also for various cementing operations, such as running casing, liners, casing with inner string, squeeze jobs, and balanced-plug cementing. There are reported cases of residual cement adhering to the inside walls of the drillstrings after the cementing operation is completed, and the work string is pulled out of the hole (POOH). The residual cement ultimately hardens, and this hardened scale cracks and flakes off in various sizes because of vibrations and pipe flexing. There is a possibility that the larger sizes of scale may catch in the bottomhole assembly (BHA), plugging the measuring while drilling (MWD) tools, downhole motor, and even the bit. Cement scale may also plug work strings used in cementing plug and squeeze operations. In offshore deepwater operations, pulling out a plugged BHA or work string could cost USD millions in lost time, depending on the depth of the wellbore. During primary cementing, where the DP is used to run the casing, the cement scale from the reused DP could plug the float equipment, which may cause the premature release of the wiper plugs, packoff at tight restriction, or affect the hanger setting tools and may result in a major job failure. A primary cause for residual cement on the inside of DP is zero velocity at the wall-fluid interface caused by a no-slip condition. A 3D displacement simulator was used to perform post-job analysis for two balanced-plug jobs on a deepwater Gulf of Mexico (GOM) well to predict the residual cement. The simulator solves momentum conservation equations for the velocity field, and a convective-diffusion equation for the concentration field. The deepwater GOM well had a work string consisting of a tapered string of 6.625-in. DP (0 to 10,500 ft) followed by 5-in. DP (10,500 to 23,800 ft) and 3.5-in. DP (23,800 to 24,800 ft). The selection, provision, and proper preparation of the DPs is solely the responsibility of the operator. The effects of wiper darts and fluid volumes on the thickness of the residual cement layer were also simulated. This type of 3D displacement simulator can be extremely valuable as a prejob cementing design tool and for post-job analyses.

Fluid invasion during cement hydration is governed by, among other factors, differential pressure between the formation fluids and the annular fluid. The primary phenomena influencing pressure in the annulus are evolution of cement slurry physical and chemical properties with time, filtrate lost to the formation, and changes in cement slurry volume during hydration. A successful procedure to design slurries to mitigate fluid invasion shall model these phenomena and provide viable methods to measure model parameters. At the same time, it should be feasible to formulate cement slurries to obtain the parameters necessary for a successful design. This paper discusses model details with emphasis on parameters, their test procedures, and equipment details. Dynamic filter-cake properties are calculated by applying compressible filtration theory on data from a modified fluid loss test. Shrinkage/expansion is measured under temperature using the API ring mold apparatus. Pressure and displacement response to filtrate loss and shrinkage/expansion is dependent on bulk modulus, shear modulus, and static gel strength (SGS) evolution of the cement slurry during hydration. Properties are measured as a function of time using sonic analysis and a rotational gel strength device. Both material properties and volume changes attributed to fluid loss and hydration showed time dependency. Furthermore, the pressure response of two realistic wells having different permeability and pore pressure profiles is analyzed. The two analyzed wells had different pressure responses, indicating that the slurry design should be customized for each well. This difference is attributed to varying capabilities of the well to compensate for volume loss by movement of cement placed adjacent to the permeable section, showing that the relative locations of the filtrate loss and potential fluid influx zones are important. Such an observation is possible only because of the ability to measure and model dynamic properties and events. The proposed methods are practical and can be realized using existing equipment with few procedural changes. Analysis based on these measurements guides the customization of slurry designs.