Cementing high temperature exploration wells present a number of challenges to well construction engineers. High bottom hole static temperature (above 100°C), very low pump rates and excessively long job times due to the constraints imposed by tight annular clearances and the use of heavy, viscous drilling muds and cement slurries, and formation complexities (salt layer, high leakoff, unstable formations) all contribute to the operational risks not only during placement of the cement slurry in the wellbore, but also later to the set cement sheath during the life of the well. Various cement systems have been applied with unsuccessful results.
A new cement formulation developed has helped to resolve the problems encountered in cementing these exploration wells and eight jobs have been completed in the field with great success. Synergistic effect between the new retarder and fluid loss control additive improve the system performance significantly such as low fluid loss rate, minimal free water, proper rheology, predictable thickening time, high resistance to salt contaminations, and no adverse effect on set cement strength. An effective laminar flow spacer was also developed and used to displace drilling muds effectively to enhance its placement and improve the cementing bond.
This paper will describe details of thorough and systematic laboratory development of the new cement system and present case histories to document its effectiveness for cementing high temperature exploration wells.