Improving Cement Bonding and Zonal Isolation in Gas Wells Located in Southern Chile

Abstract

This work describes some technologies that have been applied in several wells in southern Chile to improve zonal isolation between different reservoir sections and minimize unwanted water production; an excellent cement bond is a key requirement. There are several challenges to the success of a cement job: the presence of gas-bearing zones in the wellbore that can destabilize the cement system causing it to fail, the presence of formations sensitive to filtrates from the drilling fluids and cement, and the climatic conditions in southern Chile during winter. In addition to these factors, the well needs to be cemented without generating any formation damage that could impair the well productivity. The paper describes a multiwell solution consisting in the utilization of a solid gas migration (SGM) technology that, combined with a high-performance cement system and an engineered train of preflushes, allows achieving the ultimate goal of obtaining excellent cement quality and minimum formation damage. The SGM technology is suitable for use at very low ambient temperatures, and it provides effective gas-tight properties while minimizing the fluid loss of the slurry. The solution has proved to be extremely effective in controlling gas migration, even under extreme situations where neighboring wells presented serious sustained casing pressure (SCP) problems. The novel SGM technology utilized also allows improvements in logistics by reducing the preparation time and equipment requirements for the job, thus providing a more sustainable well construction process. In addition, the cold-tolerant additives used provide significant value when preventing nonproductive time at the wellsite and, at the same time, eliminating the disposal of mix water containing liquid additives degraded because of the freezing cycles. To date, more than 20 wells, with gas severity ranging from moderate to high, have been successfully cemented using this approach. The paper provides details of the engineering approach and examples, including cement logs.