Abstract
Poor mechanical integrity of cement sheaths during the production of oil and gas wells may cause air channeling and water channeling issues in the wells, leading to severe safety problems, and adversely affecting the safety and efficiency of the oil and gas resources production. This article focuses on a low-density cement slurry system with added floating beads. The compressive strength and flexural strength of cement stones, the mechanical integrity of cement rings, and triaxial mechanical properties were assessed. The optimal dosage of floating beads and the evolution of the cement stone’s mechanical properties and deformation ability were discussed. Bonding strengths of the first and the second interfaces were evaluated using the shrinkage test results of the cement mortar. Finally, the microscopic mechanism of the change in mechanical properties was analyzed by scanning electron microscopy. The results showed that the cement mortar exhibited the best compressive strength, mechanical integrity, and deformability after blending with 15% floating beads. At the same time, the volume shrinkage of the cement mortar mixed with 15% floating beads was the smallest, only 0.00667%, plausibly indicating good bonding with a casing and the formation to reduce the occurrence of gas channeling. Finally, the microscopic test of the cement mortar showed that the bonding between floating beads and cement was not tight, so internal cracks in the cement easily developed along the bonding part of cement and floating beads. The more floating beads were mixed, the more likely was cement mortar destroyed.
Highlights
The results showed that the cement mortar exhibited the best compressive strength, mechanical integrity, and deformability after blending with 15% floating beads
This study simulates the density of cement slurry at different formation temperatures and pressures and explores the effect of different amounts of floating beads on the mechanical properties of low-density cement slurry systems
The amount of floating beads used in this article is 15, 18, 20, 23, and 25%
Summary
Annulus compression zone and gas channeling are challenging (Bu et al, 2016; Zhao et al, 2018; Zeng et al, 2019; Bu et al, 2020a; Bayanak et al, 2020) problems in the development and production of oil and gas wells because cement rings are subjected to casing internal pressure (Bu et al, 2020b; Guo et al, 2020; Kuanhai et al, 2020; Kuanhai et al, 2021) and formation stress (Su et al, 2022). Scholars use cement, floating beads, micro-silica, and cellulose fibers to study low-density cement slurry systems (Li et al, 2014; Cheng et al, 2018). The main purpose is to use the principle of particle grading to optimize the particle size distribution between the cement slurry and low-density filling materials and to maximize the accumulation ratio between materials and reduce the gaps between material particles. This study simulates the density of cement slurry at different formation temperatures and pressures and explores the effect of different amounts of floating beads on the mechanical properties of low-density cement slurry systems. 3) Additives, mainly fluid loss agent G33S and dispersant USZ, were provided by Weihui Chemical Co., Ltd
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