Abstract
A well-known challenge in high-temperature well cementing is to prevent settling within cement slurries during placement. Many suspension additives lose their properties with temperature. However, increased loading of the suspension additives to offset the thinning would lead to unmixable slurries at the surface. Herein this paper discusses the use of a new Modified Natural Polymer (MNP) technology to address the high-temperature slurry stability challenge. This MNP was designed to aid in the suspension of solids and free water once the slurry reached an activation temperature. Below the activation point, the MNP shows a very limited impact on the slurry rheology. But once activated by temperature, the MNP can provide very effective slurry suspension even beyond the commonly seen high-temperature limit of natural polymers. MNP is also compatible with commonly used additives and has no other significant impact on the slurry properties besides suspension.
A series of tests have been conducted to demonstrate the effectiveness of MNP in various sets of conditions. A comprehensive set of tests was conducted on a 16.4 ppg Class H design where the triggered activation of the MNP is critical for mixability at the surface. BP settling tests on this slurry design were conducted from 300 to 375°F with a significant reduction of top-to-bottom density variation. A high-precision rheology study is conducted with slurries containing MNP to develop a better insight into its working mechanism. It is here demonstrated that MNP suspension capability is developed through marginal interactions between the polymer and cement particles which makes it less impacting on other additives interactions and reduces the risk for antagonistic effects.
