Effects of Well Cement Additive Particle Size and Density Towards Overall Blend Characterization
Authors: Ashraf Shameed , Muhamad Husin Rahmad Haidzar , Mohd Hafiz Fakhuma Ubaidillah 
Published: June 2021

Well cementing has evolved tremendously since its first application in the early 1900s. In the past, cement was mixed with water at the optimal ratio and combined with silica, bentonite, and additives according to the conditions of use. This simple formulation cannot serve the full breadth of oilfield applications. As a result, cement blend composition has evolved with advanced materials such as lightweight glass beads, cenospheres, polymeric beads, hematite, silica, manganese tetroxide, and many more. The wide variety of material used combined with poor understanding of the modern blend has resulted in operational issues, causing failures in blend delivery and execution. There have been cases of unfavorable blend leading to operation failure after it got stuck within the silo, unable to be pneumatically transferred. Some blend has high segregation potential, causing components to separate out, leading to problems in terms of mixing and having stable density during execution.

The focus of this study is to establish a comprehensive understanding of modern cement blend additives for seamless operational execution. Several commonly used materials have been selected to form a case study of powder additive behavior. These materials are grouped into three categories: light, medium, and heavy density, with specific gravity between 0.1 and 1.9, 2.0 and 3.9, and 4.0 and 6.0 g/cm3, respectively. Each group is further divided into subcategories based on the particle sizes of fine, medium, and coarse. These materials are then characterized in terms of flowability factor, aeration energy, and compaction ratio, which consists of the Carr index and Hausner ratio. These are typical physical flow characteristics of the bulk solids.

Results show that particle size and density significantly influence the flowability factor, aeration energy, and compaction ratio of a powder blend. In general, materials with fine particle size tend to have higher resistance to flow when evaluated through the flowability factor. Both medium- and coarse-particle additives tend to have higher flowability factor than fine-particle blends, that results in easier blend movement. Aeration energy requirements are much higher for high-density and coarse particles compared to medium and fine particles. The compaction ratio evaluation shows that coarse materials have lower tendency to compact compared to the fine and medium materials.

Based on the established understanding of individual components, mixtures are then formed with the intention of improving the overall blend character. The poor characteristics of a high-density fine material are significantly improved by combining the fine material with a lightweight cenosphere. The high aeration energy requirements of heavy coarse particles can be halved by adding lightweight glass beads. For improved behavior, a different particle size of silica materials can be mixed at optimized ratio. Combining materials to obtain optimal particle-size distribution and density is crucial to ensuring an overall blend with favorable characteristics. The behavior of individual components based on particle size and density has paved the way for effective optimization of blends for seamless operational deliverables