Ground water contamination has been a major consideration in the in the Oil and gas industry of the United States and indeed the world. Previous works have shown the reduction of cost and increased quality in intermediate cementing by the use of sodium metasilicate to replace the existing bentonite slurry system being used. The use of admixtures of 50:50 Class H (or Class C): Pozzalon with 2% bentonite have functioned effectively worldwide for nearly 50 years as lightweight slurries for situations where heavier completion cements posed a risk of exceeding low fracture gradients in a particular well bore. Pozzolanic materials are lightweight, and effectively combine with calcium hydroxide that is liberated during the hydration of Portland cement. Historically, the 2% bentonite has been utilized to assist in the specification of relatively high water-to cement ratios, and therefore lighter slurry density, without the generation of excessive free water as the cement progresses through the setting process. The bentonite has performed well in meeting this requirement, but two things remain elusive: first, its presence in typical cement slurries reduces the effectiveness of a given concentration of most commercially available fluid loss additives. Second, while the 2% (by weight of cement) volume may seem of no consequence, the shipping costs associated with moving tons of the material over a long period of time can be significant.
This study was carried out to determine whether or not there were other commercially available materials that could substitute for bentonite and yield improved slurry qualities at the same or reduced cost. Extensive testing of 50:50 slurries revealed that small quantities of sodium metasilicate (on the order of 0.5% by weight of cement) could effectively replace bentonite. Free water was controlled to the same degree, and a synergy with a commonly available fluid loss additive was discovered, allowing either (a) less total fluid loss additive for a given fluid loss control tolerance, or, (b) better fluid loss control for a given concentration of fluid loss additive and (c) current studies have also shown the possibility of wellbore water and formation water interaction being reduced due to increased strength of the slurry system being used.
The testing procedure is summarized, and relative economics associated with the systems are discussed.
The operations of oil and gas companies have come under increased scrutiny by different environmental organizations calling for more environmental responsibility. The weakening of completions over a period of time has also caused fresh concerns on reviewing the use of Bentonite for intermediate cementing. Bentonite has been used as an extender for years in the oil service industry. In recent years it has become of great concern to look into better quality control, cost savings, superior slurry performance, improved handling and logistics that could improve operations and generate savings.
In the industry today, the 50:50 Class H (or Class C): Pozzalon with 2% bentonite has been used predominantly for the control of excessive free water in cement systems, However, there has been the problem of bentonite reducing the effectiveness of fluid loss additives and the cost of having to transport this material to site has been a reason to look at better options or a substitute. The ability to control free water has been a major concern in the industry, especially with the Class H cement which has an inherent free water problem at higher water ratios. This project attempted to control free water in both class H and C, and also increase the functionality of fluid loss for given concentrations
