Preparation and effectiveness of a high-temperature anti-settling agent for well cement slurries

摘要

A high molecular weight copolymer consisting of 2-acrylamido-2-tert butyl sulfonic acid (ATBS) and N,N-dimethyl acrylamide (NNDMA) was encapsulated in a natural rubber latex matrix and evaluated relative to its functionality as thermally activated, delayed release anti-settling agent in well cementing. Successful incorporation of CaATBS-co-NNDMA was confirmed via scanning electron microscopy and energy dispersive X-ray spectroscopy. It was found that the composite material has only minor influence on the viscosity during slurry mixing at the surface, whereas starting at 80 degrees C the viscosifying polymer is gradually released and thermal thinning of cement slurry is suppressed. Thereby preventing the sedimentation of cement particles which can result in a failed cement job. The effectiveness of the composite material is owed to the release of CaATBS-co-NNDMA when the rubber matrix softens at elevated temperatures. High-temperature/high-pressure (HT/HP) consistometer testing including off/on-cycles demonstrated that the polymer successfully prevents the settling of cement at temperatures up to 180 degrees C. The encapsulated product presented here delivers a solution to mitigate high surface rheology of the cement slurry during mixing and counteract the effect of thermal thinning at elevated temperatures, thus making cementing operations more successful and safer under such conditions. The method introduced in this paper might be suitable to encapsulate any other additive which is to be released at increased temperatures.