When cementing liners, the cement must develop compressive strength at the top of the liner before drilling is resumed. If drilling is delayed in order to acquire the compressive strength at top of the liner, it can result in excessive delays on cement (WOC) time which can exceed 24 hours. Cement slurries with conventional retarders often achieve acceptable thickening times under dynamic conditions. Sometimes these cement slurries do not produce rapid compressive strength under static conditions. The aim of this study is to develop optimized retarder systems for cements that are exposed to BHST of 400 °F at the bottom of liner (BOL) and 330 °F at the top of the liner (TOL).
More than ten retarders including lignosulfonate, ethylene glycol, and aromatic polymer derivatives were evaluated to provide extended thickening times for extreme high temperature cement slurries, while having minimal effect on sonic strength development. The lab studies included comparison between various retarders and their performances of thickening time, sonic strength development, free water, fluid loss, rheology, and gas migration control.
Two new retarded systems were developed. The first system is used for non-latex cements for wells that do not show indications of gas or fluid flow. The second cement system includes latex and is recommended for cases where there is potential for gas migration. The new retarder systems were effectively applied in the field. The paper will address lab studies that led to the development of new retarders.