Measurement Procedures and Analysis of Fluid Invasion Drivers During Cement Hydration

Abstract

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.